essay about earthquake and volcanoes

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Effects of earthquakes and volcanoes on people and the environment

The effects of earthquakes and volcanoes are typically classified as being either primary or secondary.

Primary effects are the direct result of an earthquake or volcanic eruption, such as buildings collapsing due to the movement of the earth or loss of life from pyroclastic flows.

Secondary effects are those that occur as the result of primary effects . Examples include fires caused by the rupture of gas pipes caused by an earthquake or homelessness caused by the loss of buildings.

Impacts of earthquakes and volcanoes on people

The impacts of volcanoes and earthquakes will vary depending on a range of factors at any particular place, however, earthquakes and volcanoes have a similar range of hazardous results.

Loss of life

Loss of life occurs in a many ways including collapsing buildings, bridges and elevated roads, disease and fire.

Cutting basic amenities

The loss of basic ammenities such as fresh water, gas and electricity due to damage to power lines, gas pipelines, water and sewage pipes.

Collapse of buildings

Earthquakes can lead to the destruction of buildings. Those not destroyed can be weakened and may subsequently collapse due to aftershocks. People may become homeless.

Damage to transport infrastructure

Damage to transport infrastruture, such as roads, rail and airports can make access to earthquake affected areas very difficult.

Loss of crops and trees

Pyroclastic flows, lahars and ashfall can destroy crops in the surrounding area, destroying people’s livelihoods.

Death of fish

Ashfall can lead to the death of fish in rivers, lakes and hatcheries.

Spread of disease

Due to the lack of clean water, poor access to medicine, overcrowding in temporary camps and lack of sanitation disease can easily spread.

Loss of jobs and business

The loss of factories and offices when earthquakes and volcanoes occur can lead to the loss of businesses and jobs.

Higher insurance premiums

Areas affected by volcanic eruptions and earthquakes can lead to higher insurance premiums or none being offered at all. The increase in premiums may out-price some companies/individuals making it impossible to get insurance cover.

Loss of human life

The loss of human life is the most significant impact of volcanic eruptions and earthquakes. LICs and NEEs, such as Haiti and Pakistan, do not have the resources to prepare for and respond to hazards such as earthquakes and volcanoes compared to HICs such as Japan and the USA.

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Effects of earthquakes and volcanoes

What factors affect the impact of earthquakes?

The amount of damage caused by earthquakes depends on a combination of factors. These include:

• the strength of the earthquake and subsequent aftershocks
• the depth of the earthquake, the deeper the earthquake, the more energy is absorbed by the crust above them
• the distance from the epicentre, the further away from the epicentre the weaker the seismic waves
• the geology of an area, looser rocks, such as sedimentary, are more likely to liquefy and cause buildings and structures to sink into the ground
• the quality of building and construction materials
• the density of buildings as the higher the density, the greater the chance of swaying buildings to affect others
• the number of storeys – the taller the buildings, the more likely they are to sway and collapse
• the population density – the higher the population density, the more likely there are to be casualties
• the time of the day the earthquake occurs – at night people are likely to be sleeping in residential areas – older residential areas are more likely to be affected by earthquake damage
• secondary hazards such as tsunamis close to the coast, landslides and rockfalls in mountainous areas and fires caused by broken gas pipes in urban areas.
• contamination – caused by water supplies becoming contaminated as they mix with sewage

What factors affect the impact of volcanoes?

There are a wide variety of hazards that can injure and kill people and destroy property from volcanic eruptions. However, unlike earthquakes, volcanic eruptions can affect people and places hundreds of miles away. In addition to this, volcanic eruptions can even affect global climate.

Explosive eruptions can result in huge volumes of solid and molten rock fragments, known as tephra, volcanic gases and ash high into the atmosphere. In some instances, this has been as high as 20 km above a volcano in just 30 minutes. Volcanic ash in the atmosphere presents a considerable hazard to aeroplanes. Following the eruption of the Icelandic volcano Eyjafjallajökull in 2010, large swathes of air space across Europe was closed due to the hazard ash in the atmosphere presented.

Made of up tiny glass particles and pulverized rock, ash can be spewed tens of thousands of feet into the air, reaching jet cruising altitude. It’s abrasive enough to erode the blades of the compressor (which increases the pressure of the air that feeds the jet engine), reducing its efficiency. The ash that gets into the combustion chamber can melt, producing a substance like molten glass. That then solidifies on the turbine blades, blocking airflow, and potentially resulting in engine failure.

Following a significant eruption ash clouds can extend hundreds of kilometres downwind of the volcano. When this ash falls, it can damage crops, machinery and electronics. Significant ashfall can result in the collapse of buildings due to its weight.

Volcanic eruptions can emit significant volumes of toxic gasses during eruptions. Even when not erupting, gases are released through small openings called fumaroles. 90% of all gas emitted is water vapour; however, carbon dioxide and fluorine gas can also be released with deadly consequences.

On 21 August 1986, one of the strangest and most mysterious natural disasters in history took place at Lake Nyos – a lake formed atop a volcanic crater in northwest Cameroon. Without warning, the lake released hundreds of thousands of tonnes of toxic carbon dioxide – estimates range from 300,000 to up to 1.6 million – and this silent death cloud spread out over the countryside at nearly 100 km/h (62 mph), suffocating an estimated 1,746 people and more than 3,500 livestock within minutes. As carbon dioxide is heavier than air, it flowed into valleys below the crater, causing the significant loss of life.

Fluorine gas, which in high concentrations can be deadly, is absorbed into volcanic ash particles that fall to the ground. The particles can poison livestock grazing on ash-covered grass. It can also contaminate water supplies.

Pyroclastic flows, deadly avalanches of hot ash, gas and rock fragments, can result from explosive eruptions or the collapse of growing lava domes. Pyroclastic flows often follow the path of least resistance, such as valleys. The deadliest pyroclastic flow in recorded history was caused by the eruption of Mount Pelée, Martinique in 1902 when around 30 000 people died. A pyroclastic flow from Mount Vesuvius in 79 AD led to over 3360 deaths in the Roman settlement of Pompeii.

The images below show the impact of a pyroclastic flow from the Fuego volcano on the town of San Miguel Los Lotes, Guatemala in 2018.

Flows of volcanic ash, mud, rock and water, known as lahars, are a deadly after-effect of volcanic eruptions. In 1985, lahars contributed to the 25 000 death-toll following the eruption of the Nevado del Ruiz volcano in Colombia.

Why do people live close to volcanoes?

Despite their hazardous nature, many people live in areas that are likely to experience volcanic eruptions. They do so for several reasons, including:

• Volcanoes provide raw materials – sulphur, gold, zinc and diamonds can be mined and sold.

• Volcanoes attract tourists – locals provide guided tours, and there are business opportunities in tourism , such a providing accommodation and food.
• Volcanic soils are very fertile, and crop yields are high – volcanic soils on the flanks of volcanoes and the surrounding area provide excellent opportunities to farmers.

Geothermal energy power station in Iceland

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Earthquake Essay for Students and Children

500+ Words Essay on Earthquake

Simply speaking, Earthquake means the shaking of the Earth’s surface. It is a sudden trembling of the surface of the Earth. Earthquakes certainly are a terrible natural disaster. Furthermore, Earthquakes can cause huge damage to life and property. Some Earthquakes are weak in nature and probably go unnoticed. In contrast, some Earthquakes are major and violent. The major Earthquakes are almost always devastating in nature. Most noteworthy, the occurrence of an Earthquake is quite unpredictable. This is what makes them so dangerous.

Types of Earthquake

Tectonic Earthquake: The Earth’s crust comprises of the slab of rocks of uneven shapes. These slab of rocks are tectonic plates. Furthermore, there is energy stored here. This energy causes tectonic plates to push away from each other or towards each other. As time passes, the energy and movement build up pressure between two plates.

Therefore, this enormous pressure causes the fault line to form. Also, the center point of this disturbance is the focus of the Earthquake. Consequently, waves of energy travel from focus to the surface. This results in shaking of the surface.

Volcanic Earthquake: This Earthquake is related to volcanic activity. Above all, the magnitude of such Earthquakes is weak. These Earthquakes are of two types. The first type is Volcano-tectonic earthquake. Here tremors occur due to injection or withdrawal of Magma. In contrast, the second type is Long-period earthquake. Here Earthquake occurs due to the pressure changes among the Earth’s layers.

Collapse Earthquake: These Earthquakes occur in the caverns and mines. Furthermore, these Earthquakes are of weak magnitude. Undergrounds blasts are probably the cause of collapsing of mines. Above all, this collapsing of mines causes seismic waves. Consequently, these seismic waves cause an Earthquake.

Explosive Earthquake: These Earthquakes almost always occur due to the testing of nuclear weapons. When a nuclear weapon detonates, a big blast occurs. This results in the release of a huge amount of energy. This probably results in Earthquakes.

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Effects of Earthquakes

First of all, the shaking of the ground is the most notable effect of the Earthquake. Furthermore, ground rupture also occurs along with shaking. This results in severe damage to infrastructure facilities. The severity of the Earthquake depends upon the magnitude and distance from the epicenter. Also, the local geographical conditions play a role in determining the severity. Ground rupture refers to the visible breaking of the Earth’s surface.

Another significant effect of Earthquake is landslides. Landslides occur due to slope instability. This slope instability happens because of Earthquake.

Earthquakes can cause soil liquefaction. This happens when water-saturated granular material loses its strength. Therefore, it transforms from solid to a liquid. Consequently, rigid structures sink into the liquefied deposits.

Earthquakes can result in fires. This happens because Earthquake damages the electric power and gas lines. Above all, it becomes extremely difficult to stop a fire once it begins.

Earthquakes can also create the infamous Tsunamis. Tsunamis are long-wavelength sea waves. These sea waves are caused by the sudden or abrupt movement of large volumes of water. This is because of an Earthquake in the ocean. Above all, Tsunamis can travel at a speed of 600-800 kilometers per hour. These tsunamis can cause massive destruction when they hit the sea coast.

In conclusion, an Earthquake is a great and terrifying phenomenon of Earth. It shows the frailty of humans against nature. It is a tremendous occurrence that certainly shocks everyone. Above all, Earthquake lasts only for a few seconds but can cause unimaginable damage.

FAQs on Earthquake

Q1 Why does an explosive Earthquake occurs?

A1 An explosive Earthquake occurs due to the testing of nuclear weapons.

Q2 Why do landslides occur because of Earthquake?

A2 Landslides happen due to slope instability. Most noteworthy, this slope instability is caused by an Earthquake.

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How are volcanoes and earthquakes interrelated?

• Updated 17/11/22
• Read time 5 minutes

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Both volcanoes and earthquakes occur due to movement of the Earth’s tectonic plates. They are both caused by the heat and energy releasing from the Earth’s core. Earthquakes can trigger volcanic eruptions through severe movement of tectonic plates. Similarly, volcanoes can trigger earthquakes through the movement of magma within a volcano. Therefore, one aspect of how are volcanoes and earthquakes interrelated is the cyclical relationship where earthquakes cause volcanic eruptions and magma movement causes earthquakes.

Earthquakes and volcanic eruptions in itself are dangerous natural phenomena which poses risk to humans. Furthermore, tsunamis are an equally deadly secondary effect caused by underwater disturbances such as earthquakes, volcanic activity, landslides, underwater explosions or meteorite impacts which pose significant danger to human lives.

What are tectonic plates and how do they explain volcanoes and earthquakes?

The outer layer of the Earth is made up of solid rock, called lithosphere. The lithosphere is broken up into 17 major separate pieces that fit together like a bad jigsaw puzzle. A piece of the puzzle is called a tectonic plate . The plates are horribly placed, with overlapping pieces, gaps, and are forced to fit with each other even when they don’t. Because the tectonic plates don’t go well together, it creates earthquakes and volcanic activity when two plates collide, diverge or slide past each other.

There are three types of boundaries caused by tectonic plates on Earth: first, transform boundaries when two plates slide or grind past each other. Transform boundaries are horizontal movements of plates and do not create or destroy plates. Second, divergent boundaries when two plates create a gap in between each other. Divergent boundaries create ocean basins when plates move apart from one another. Third, convergent boundaries when two plates crash towards each other and overlap to form a subduction zone.

Tectonic plates are extremely large and can encompass both land and ocean. These tectonic plates interact with one another because of the Earth’s internal heat. This heat causes movement of material beneath the Earth’s crust and releases energy in the form of earthquakes and volcanic eruptions. Interactions between the tectonic plates occurs in three main places: first, oceanic-continental convergence, where the continent meets the ocean. Second, continental-continental convergence, where two continents meet. Last, oceanic-oceanic convergence, where two oceans meet.

So, how are volcanoes and earthquakes interrelated? Both volcanoes and earthquakes are caused along the boundaries of tectonic plates due to their movements and interactions.

How dangerous are volcanoes and earthquakes to humans?

How many deaths there are and how severe a natural disaster is depends on the interactions we have as humans with our environment. A strong earthquake can be completely overlooked if it happens in the middle of land where hardly any people live in, for example in December 2003, when a 6.5 magnitude earthquake in Central California killed two people. Consequently, a similar earthquake in a densely populated metropolitan area can cause many deaths, injuries and destruction of property, for example, a 6.6 magnitude earthquake in Bam, Iran killing 30,000 people, injuring 30,000 more and destroying 85% of property.

The same goes for volcanic eruptions, if an underwater volcano erupted in the middle of the ocean, it would have little impact to humans living far inland. However, if the volcano had been dormant for a significant amount of time and humans started populating the land close to the base of a volcano it would be devastating should it ever erupt. Further, indirect consequences of a volcanic eruption can have a greater impact than the eruption itself. For example, volcanic ash can induce climate change that have serious agricultural, economic, and sociological impacts on people’s lives.

Read these articles to learn more about the structure of the volcano and the internal structure of the volcano .

To find out more about where the next volcano will erupt in Australia, read this article.

Tsunamis as a result of earthquakes or volcanic activity

Tsunamis are giant waves that occur when a large volume of water is displaced. The most common causes of underwater disturbances that lead to tsunamis are earthquakes and volcanic eruptions, especially because most volcanoes are underwater. Although tsunamis can also be caused by landslides, meteorite impacts and underwater explosions. Tsunami waves travel extremely fast, with wave speeds reaching up to 900 km/h in deep water. The waves get taller the closer they reach the shoreline because of rapidly decreasing depth of the sea floor, and slow down to 20 – 50 km/h.

We can deduce that volcanoes and earthquakes are caused by tectonic plate movements, they both pose a significant danger to humans, and result in deadly secondary effects like tsunamis.

Additional Reading

https://web.archive.org/web/20120913041924/http://www.enviroliteracy.org/nsfmod/NaturesFury.pdf

https://australian.museum/blog-archive/science/earthquakes-and-tsunamis/

https://australian.museum/learn/minerals/shaping-earth/plate-tectonic-processes/

https://media.australian.museum/media/dd/Uploads/Documents/4645/volcano_structure.134d97b.pdf

https://australian.museum/learn/minerals/shaping-earth/structure-of-volcanoes/

https://australian.museum/blog-archive/science/amri-where-next-volcano-erupt-in-australia/

The Australian Museum respects and acknowledges the Gadigal people as the First Peoples and Traditional Custodians of the land and waterways on which the Museum stands.

Image credit: gadigal yilimung (shield) made by Uncle Charles  Chicka  Madden

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Why is an earthquake dangerous?

What are earthquake waves, how is earthquake magnitude measured, where do earthquakes occur.

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Over the centuries, earthquakes have been responsible for millions of deaths and an incalculable amount of damage to property. Depending on their intensity, earthquakes (specifically, the degree to which they cause the ground’s surface to shake) can topple buildings and bridges , rupture gas pipelines and other infrastructure, and trigger landslides , tsunamis , and volcanoes .  These phenomena are primarily responsible for deaths and injuries. Very great earthquakes occur on average about once per year.

Earthquake waves, more commonly known as seismic waves , are vibrations generated by an earthquake and propagated within Earth or along its surface. There are four principal types of elastic waves: two, primary and secondary waves, travel within Earth, whereas the other two, Rayleigh and Love waves, called surface waves, travel along its surface. In addition, seismic waves can be produced artificially by explosions.

Magnitude is a measure of the amplitude (height) of the seismic waves an earthquake’s source produces as recorded by seismographs . Seismologist Charles F. Richter created an earthquake magnitude scale using the logarithm of the largest seismic wave’s amplitude to base 10. Richter’s scale was originally for measuring the magnitude of earthquakes from magnitudes 3 to 7, limiting its usefulness. Today the moment magnitude scale, a closer measure of an earthquake’s total energy release, is preferred.

Earthquakes can occur anywhere, but they occur mainly along fault lines (planar or curved fractures in the rocks of Earth’s crust ), where compressional or tensional forces move rocks on opposite sides of a fracture. Faults extend from a few centimetres to many hundreds of kilometres. In addition, most of the world’s earthquakes occur within the Ring of Fire , a long horseshoe-shaped belt of earthquake epicentres , volcanoes , and tectonic plate boundaries fringing the Pacific basin .

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earthquake , any sudden shaking of the ground caused by the passage of seismic waves through Earth ’s rocks. Seismic waves are produced when some form of energy stored in Earth’s crust is suddenly released, usually when masses of rock straining against one another suddenly fracture and “slip.” Earthquakes occur most often along geologic faults , narrow zones where rock masses move in relation to one another. The major fault lines of the world are located at the fringes of the huge tectonic plates that make up Earth’s crust. ( See the table of major earthquakes.)

Little was understood about earthquakes until the emergence of seismology at the beginning of the 20th century. Seismology , which involves the scientific study of all aspects of earthquakes, has yielded answers to such long-standing questions as why and how earthquakes occur.

About 50,000 earthquakes large enough to be noticed without the aid of instruments occur annually over the entire Earth. Of these, approximately 100 are of sufficient size to produce substantial damage if their centres are near areas of habitation. Very great earthquakes occur on average about once per year. Over the centuries they have been responsible for millions of deaths and an incalculable amount of damage to property.

The nature of earthquakes

Causes of earthquakes.

Earth’s major earthquakes occur mainly in belts coinciding with the margins of tectonic plates. This has long been apparent from early catalogs of felt earthquakes and is even more readily discernible in modern seismicity maps, which show instrumentally determined epicentres. The most important earthquake belt is the Circum-Pacific Belt , which affects many populated coastal regions around the Pacific Ocean —for example, those of New Zealand , New Guinea , Japan , the Aleutian Islands , Alaska , and the western coasts of North and South America . It is estimated that 80 percent of the energy presently released in earthquakes comes from those whose epicentres are in this belt. The seismic activity is by no means uniform throughout the belt, and there are a number of branches at various points. Because at many places the Circum-Pacific Belt is associated with volcanic activity , it has been popularly dubbed the “Pacific Ring of Fire .”

A second belt, known as the Alpide Belt , passes through the Mediterranean region eastward through Asia and joins the Circum-Pacific Belt in the East Indies . The energy released in earthquakes from this belt is about 15 percent of the world total. There also are striking connected belts of seismic activity, mainly along oceanic ridges —including those in the Arctic Ocean , the Atlantic Ocean , and the western Indian Ocean —and along the rift valleys of East Africa . This global seismicity distribution is best understood in terms of its plate tectonic setting .

Natural forces

Earthquakes are caused by the sudden release of energy within some limited region of the rocks of the Earth . The energy can be released by elastic strain , gravity, chemical reactions, or even the motion of massive bodies. Of all these the release of elastic strain is the most important cause, because this form of energy is the only kind that can be stored in sufficient quantity in the Earth to produce major disturbances. Earthquakes associated with this type of energy release are called tectonic earthquakes.

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Earthquakes and Volcanoes

Earthquakes and volcanic eruptions are incredible and dramatic natural events. On this page you can learn more about the science behind them:

• Bárðarbunga-Holuhraun Eruption Learn about the 2014 Bárðarbunga eruption and the massive Holuhraun lava field that it created.
• Fascinating Facts Discover interesting facts that you might not know about earthquakes and volcanoes.

Bárðarbunga-Holuhraun Eruption

Iceland sits on crack in the surface of the Earth where two tectonic plates (large blocks that make up the outer most layer of the Earth) are ripping apart from each other. These two blocks are moving apart at around 2 cm per year (approximately the rate that your finger nails grow) and are slowly widening the Atlantic Ocean; increasing the distance from Europe to North America. As the tectonic plates split apart magma (molten rock) wells up from below forming volcanoes, which creates new land in between. This rifting process is happening all the way down the middle of the Atlantic Ocean beneath the sea. But at Iceland we see the process on land because a hot upwelling from deep within the Earth also sits beneath Iceland, pushing it upwards out of the sea and making the area even more volcanically active.

Iceland has over 30 active volcanic systems, which have a central volcano in the middle with long cracks spreading outwards to the north and south (fissure swarms). Magma (molten rock) can erupt from the central volcano itself, or travel through the cracks of the fissure swarm to create long lines of eruptions far from the volcano itself.

The main volcanic rift zones in Iceland, with Bárðarbunga volcano beneath the Vatnajökull ice sheet.

When you think of Icelandic volcanoes, the one you will probably remember is the eruption of the volcano with the long, hard to pronounce name that had news readers getting their tongues in a twist: Eyjafjallajökull, which sits under a glacier in southern Iceland. This volcano erupted in 2010 and was all over the news because it produced so much ash that it grounded 100,000 flights and closed European air space. The main reason why this eruption was so ash heavy was due to the interaction of the hot magma erupting under the cold overlying ice. But a couple of years later in 2014 there was another eruption in Iceland, at a volcano called Bárðarbunga. It was the largest eruption in Iceland in over 200 years, and was 10 times bigger than than the eruption of Eyjafjallajökull, but it didn't ground a single flight.

The eruption of Eyjafjallajökull in 2010 created a large ash plume that blew across western Europe .

Bárðarbunga volcano is right in the middle of Iceland in the remote and uninhabited highlands. It sits underneath the massive Vatnajökull glacier, covered by around 800 m of thick ice. Scientists first knew something interesting was happening at Bárðarbunga in August of 2014 when hundreds of tiny earthquakes were detected within the volcano deep below the ice. Teams rushed out to deploy more seismic instruments to record the earthquakes and determine where they were happening more accurately. Scientists were flown up onto the glacier in helicopters, before speeding around on snow scooters to get the essential instruments out as quickly as possible.

Bárðarbunga volcano beneath the Vatnajökull ice sheet.

Over the next two weeks the country watched closely as the 30,000 tiny earthquakes tracked the underground movement of the magma as it cracked a 46 km long path through the earth’s crust. The earthquake activity moved gradually northwards, away from the volcano at 6 km down within the earth, as authorities and scientists tried to guess where and when the magma would move upwards and erupt at the surface. Would the eruption happen under the glacier producing an ash heavy eruption like Eyjafjallajökull, or would it travel far enough away from the glacier that it wouldn't interact with the ice? Or maybe it wouldn't erupt at all, and the molten rock would stay deep within the earth, cooling and solidifying to form an igneous intrusion? The magma movement was also tracked using GPS and satellite measurements. The GPS were able to measure ground movement caused by the magma pushing into the earth and shoving material outwards to either side by up to 1.5 m. This helped scientists to understand the shape that the magma was flowing in—a vertical sheet of molten rock known as a dyke, about 5 m wide.

3-D visualisation of earthquake epicentres through time as the magmatic dyke propagated from the Bárðarbunga central volcano to the Holuhraun eruption site.

The dyke advanced in rapid bursts with an average speed of 2 km per hour, reaching speeds of up to 4.7 km per hour. In the end the dyke travelled 46 km away from the feeder volcano Bárðarbunga before erupting at the surface on a river flood plain away from the glacier. The eruption, which was named Holuhraun, saw runny fluid lava thrown up to 200 m into the air (higher than Big Ben!), in pulsating fire fountains, before flowing away as rivers of molten rock. There was no central eruption point, instead the eruption happened all the way down the length of a 1.5 km long eruptive fissure that over time concentrated down to a few craters, and finally to one main crater called Baugur. The amount of thermal energy the eruption produced was tremendous; equivalent to the energy of a Hiroshima sized atomic bomb being set off every 2 minutes!

The Bárðarbunga-Holuhraun eruption in action, with a lava flow extending across the sandur and volcanic gases issuing from the volcanic vent.

Footage of the 2014 Bárðarbunga-Holuhraun eruption.

The eruption lasted for 6 months, eventually stopping in February 2015. By then it had produced 1.6 km 3 of lava, covering an area of 85 km 2 – large enough to cover the city of Cambridge twice ( how much of your area would it have covered? ). Because there was no interaction with ice, only a minute amount of ash was produced. However it did release around 11 M tones of SO 2 – more than the whole of Europe produces in a year! This was the main hazard of the eruption as the gas was blown around on the wind affecting large numbers of the population. Ground level concentrations of SO 2 exceeded health limits over most of Iceland for days to weeks, with the high concentrations of SO 2 can cause breathing difficulties and eye irritation.

The extent of the Holuhraun lava flow in red.

It's very important to carefully monitor volcanoes to try and understand what kind of eruption they might have and what hazards that could present. The Holuhraun eruption was not hazardous to planes since it was an effusive eruption and it didn’t create a huge eruption column, but if the eruption had happened under the ice it would have been a completely different story. Measuring the tiny earthquakes that happen in volcanoes, gives us a powerful tool we can use to see inside the earth and track where molten rock is moving beneath the surface. Keeping track of these observations can help inform public bodies, aiding their decision making and their planning of hazard mitigation strategies.

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Fascinating Facts

Iceland facts.

• The population of Iceland is 330,000 , or approximately the population of Reading.
• Two-thirds of the Icelandic population live in the capital city, Reykjavik .
• More than one million people visit Iceland each year on holiday, about three times its population.
• All of Iceland's heating and electricity is renewable, either from hydroelectric or geothermal methods.
• The UK went to war with Iceland once over fish!
• Good morning in Icelandic is ‘Góðan dag’ .
• An earthquake swarm precedes eruption of the Icelandic volcano Hekla by 30 minutes, which is unhelpful if you are on the volcano, but enough time to get the news helicopters in the air from Reykjavik!
• There are about 130 volcanoes in Iceland.

Bárðarbunga- Holuhraun eruption facts

• The Holuhraun lava flow covers an area of 84 km 2 .
• During eruption, lava fountains sprayed lava up to 150 m high , which is taller than Big Ben!
• The eruption released vast amounts of thermal energy, equivalent to: releasing a Hiroshima atomic bomb every minute (in the first month), and every two minutes (on average over the six-month-long eruption).
• The Holuhraun lava flow released 100 million tonnes of sulphur dioxide, which is equivalent to the annual emissions of Europe.
• More than 30,000  small earthquakes were detected accompanying the magma intrusion.
• The peak rate of magma release was around  500 tonnes per second .
• Members of the Volcano Seismology Group from the University of Cambridge were the first people to see the eruption with their own eyes. They tracked the eruption in collaboration with the Icelandic Met Office and the University of Iceland during the first weeks of the eruption before they had to (reluctantly) go home.
• Instruments were placed so close to the eruption site that they had to be rescued from the advancing lava.
• The intrusion, and subsequent lava flow, was monitored in real-time by more than 100 seismometers, more than 30 GPS instruments, three satellites, and four webcams.

Eyjafjallajökull eruption facts

• The Eyjafjallajökull eruption ejected ash 35,000 feet into the air.
• The Eyjafjallajökull ash cloud grounded over 100,000 flights, which cost the aviation industry an estimated   £1.1 billion .
• To volcano’s name is pronounced: "EY - A - FYAT - LA - YO - KUTL" .
• The eruption caused several glacial floods (jökulhaups) when hot magma melted ice in the overlying glacier.
• Small earthquakes were detected by the Cambridge Volcano Seismology Group down to a depth of 30 km below the surface, as molten rock stored at depth migrated during the eruption.

Earthquake and seismology facts

• The magnitude scale of earthquakes is logarithmic, so every step up the scale is an earthquake ten times bigger. A magnitude 2.0 event is, therefore, ten million times smaller than the 2004 boxing day earthquake (magnitude 9.0).
• Humans have only ever dug to a depth of 12 km; less than 1% of the Earth's total thickness. The only reason we know anything about the internal structure of the Earth is because earthquake waves travel through it, and become modified by the material that they travel through.
• The United States Geological Survey (USGS) estimates that several million earthquakes occur in the Earth each year. Many go undetected because they hit remote areas or have very small magnitudes. The NEIC (National Earthquake Information Centre) now locates about 50 earthquakes each day (larger than magnitude 4.5), or around 20,000 a year.
• We get earthquakes in the UK, a few every couple of days. However, they are just very small, generally less than magnitude 2, which means that they are just too small for people to feel.
• The largest earthquake to ever happen in the UK was a magnitude 6.1 off the east coast of England in the North Sea.
• The most damaging earthquake in the UK in recent history was in 1884 near Colchester.  We don’t know exactly how large it was (probably around magnitude 4.5), but historical records show that some 1200 buildings required repairs, and three to five people were killed.

Volcano facts

• There are about 1500 active volcanoes in the world.
• 300 million, or one-in-twenty, people in the world live within the 'danger range' of an active volcano.
• About 1,500 different volcanoes have erupted over the past 10,000 years, but only about 60 erupt each year. On any given day, there are about 20 volcanoes erupting somewhere in the world.
• Many volcanoes are underwater and erupt onto the sea floor.

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Plate tectonics, volcanoes and earthquakes.

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The Earth rumbles and a hiss of steam issues from the top of Mt Ruapehu. Are these two events related? Is the earthquake caused by the volcano? Or is the steam caused by the earthquake?

Tectonic plates

When Alfred Wegener first proposed the idea of continental drift (the precursor idea to plate tectonic theory), it didn’t quite explain the full story. While he correctly showed that Africa and South America fitted together, his model wasn’t able to explain the violent forces that occur around the Earth’s crust.

It wasn’t until the 1960s that a full explanation began to develop – the theory of plate tectonics. This theory explained many pieces of the puzzle that scientists had observed, for example, continental fit, matching geology, past glaciation, movements of the ocean floor and the location of fossils of ancient animals and plants.

Scientists now believe that the crust of the Earth consists of rigid interconnecting plates (6 major plates and a few smaller ones). Plates are thought to float on the partially molten mantle, moving away from oceanic ridges where new plate material is produced and moving past each other or colliding along plate boundaries. Earthquakes and volcanoes are related to this movement.

Explore plate tectonics further.

Colliding plates

Where plates come into contact, energy is released. Plates sliding past each other cause friction and heat. Subducting plates melt into the mantle, and diverging plates create new crust material.

Subducting plates, where one tectonic plate is being driven under another, are associated with volcanoes and earthquakes. This activity is focused along the edge of the plate boundary where two plates come into contact, forming regions such as the Pacific Ring of Fire – a chain of earthquake and volcanic activity around the edge of the Pacific Ocean – which generates 75% of the world’s volcanoes and 80% of the world’s earthquakes.

Diverging plates

When plates move away from each other, the space between them gets filled with material, which rises to the surface, cools and forms mid-oceanic ridges. The Pacific Ocean is growing wider by about 18 cm per year as the plates diverge and the mid-oceanic ridge is built up.

Subducting plates and volcanoes

Plate material that is produced along the ocean floor is generally quite dense and relatively heavy. Continental plates don’t tend to get subducted. When oceanic plate is pushed from the mid-ocean ridge towards a plate boundary with a continental plate, it tends to subduct or dive below the continental crust. In this process, water is also being subducted with the oceanic plate. Friction increases the heat along such boundaries, which causes this material to melt and mix the oceanic plate material, the continental plate material and the water.

Andesite volcanoes tend to form at these subduction boundaries. This may have something to do with differences in plate densities and the release of gases, such as water vapour. As more heat is being produced through the subduction process, the mix of more and less volatile ingredients causes changes in density and pressure, which are linked to volcanic activity.

Volcanoes and earthquakes

Volcanoes and earthquakes are often found in the same place, but are they related? Does one trigger the other? The answer seems to be yes – but not always. They are sometimes linked but are often independent events.

When a volcano erupts, the pressure of the rising magma forcing its way through the crust to the surface will often trigger earthquake activity. Scientists have been able to demonstrate this link and also know what type of earthquake to look for.

Conversely, an earthquake may trigger subsequent eruptions. As the crust changes and moves in a major earthquake, fissures or cracks can form that may act as pipelines for magma and future volcanoes. This is harder to monitor and test and is an area of active research.

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There are many volcanoes in the Pacific, including the very large Hunga Tonga–Hunga Haʻapa underwater one. Read about the devastating Hunga Tonga–Hunga Haʻapa volcanic eruption in January 2022, the tsunami that followed, and what we might expect next? This article looks at what we’ve learnt a year later about this violent eruption and predicting future submarine volcanic eruptions.

Realistic contexts connect students to authentic scientific processes and purposes, it's all explained in:

• Earthquakes resources – planning pathways
• Volcanoes resources – planning pathways

Earthquakes is a collection supports the House of Science Earthquakes resource kit – but it is also useful for anyone exploring Rūaumoko, what's inside the Earth, plate tectonics, seismic waves and engineering designed to keep us safe.

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Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing (2017)

Chapter: 1 introduction, 1 introduction.

Volcanoes are a key part of the Earth system. Most of Earth’s atmosphere, water, and crust were delivered by volcanoes, and volcanoes continue to recycle earth materials. Volcanic eruptions are common. More than a dozen are usually erupting at any time somewhere on Earth, and close to 100 erupt in any year ( Loughlin et al., 2015 ).

Volcano landforms and eruptive behavior are diverse, reflecting the large number and complexity of interacting processes that govern the generation, storage, ascent, and eruption of magmas. Eruptions are influenced by the tectonic setting, the properties of Earth’s crust, and the history of the volcano. Yet, despite the great variability in the ways volcanoes erupt, eruptions are all governed by a common set of physical and chemical processes. Understanding how volcanoes form, how they erupt, and their consequences requires an understanding of the processes that cause rocks to melt and change composition, how magma is stored in the crust and then rises to the surface, and the interaction of magma with its surroundings. Our understanding of how volcanoes work and their consequences is also shared with the millions of people who visit U.S. volcano national parks each year.

Volcanoes have enormous destructive power. Eruptions can change weather patterns, disrupt climate, and cause widespread human suffering and, in the past, mass extinctions. Globally, volcanic eruptions caused about 80,000 deaths during the 20th century ( Sigurdsson et al., 2015 ). Even modest eruptions, such as the 2010 Eyjafjallajökull eruption in Iceland, have multibillion-dollar global impacts through disruption of air traffic. The 2014 steam explosion at Mount Ontake, Japan, killed 57 people without any magma reaching the surface. Many volcanoes in the United States have the potential for much larger eruptions, such as the 1912 eruption of Katmai, Alaska, the largest volcanic eruption of the 20th century ( Hildreth and Fierstein, 2012 ). The 2008 eruption of the unmonitored Kasatochi volcano, Alaska, distributed volcanic gases over most of the continental United States within a week ( Figure 1.1 ).

Finally, volcanoes are important economically. Volcanic heat provides low-carbon geothermal energy. U.S. generation of geothermal energy accounts for nearly one-quarter of the global capacity ( Bertani, 2015 ). In addition, volcanoes act as magmatic and hydrothermal distilleries that create ore deposits, including gold and copper ores.

Moderate to large volcanic eruptions are infrequent yet high-consequence events. The impact of the largest possible eruption, similar to the super-eruptions at Yellowstone, Wyoming; Long Valley, California; or Valles Caldera, New Mexico, would exceed that of any other terrestrial natural event. Volcanoes pose the greatest natural hazard over time scales of several decades and longer, and at longer time scales they have the potential for global catastrophe ( Figure 1.2 ). While

the continental United States has not suffered a fatal eruption since 1980 at Mount St. Helens, the threat has only increased as more people move into volcanic areas.

Volcanic eruptions evolve over very different temporal and spatial scales than most other natural hazards ( Figure 1.3 ). In particular, many eruptions are preceded by signs of unrest that can serve as warnings, and an eruption itself often persists for an extended period of time. For example, the eruption of Kilauea Volcano in Hawaii has continued since 1983. We also know the locations of many volcanoes and, hence, where most eruptions will occur. For these reasons, the impacts of at least some types of volcanic eruptions should be easier to mitigate than other natural hazards.

Anticipating the largest volcanic eruptions is possible. Magma must rise to Earth’s surface and this movement is usually accompanied by precursors—changes in seismic, deformation, and geochemical signals that can be recorded by ground-based and space-borne instruments. However, depending on the monitoring infrastructure, precursors may present themselves over time scales that range from a few hours (e.g., 2002 Reventador, Ecuador, and 2015 Calbuco, Chile) to decades before eruption (e.g., 1994 Rabaul, Papua New Guinea). Moreover, not all signals of volcanic unrest are immediate precursors to surface eruptions (e.g., currently Long Valley, California, and Campi Flegrei, Italy).

Probabilistic forecasts account for this uncertainty using all potential eruption scenarios and all relevant data. An important consideration is that the historical record is short and biased. The instrumented record is even shorter and, for most volcanoes, spans only the last few decades—a miniscule fraction of their lifetime. Knowledge can be extended qualitatively using field studies of volcanic deposits, historical accounts, and proxy data, such as ice and marine sediment cores and speleothem (cave) records. Yet, these too are biased because they commonly do not record small to moderate eruptions.

Understanding volcanic eruptions requires contributions from a wide range of disciplines and approaches. Geologic studies play a critical role in reconstructing the past eruption history of volcanoes,

especially of the largest events, and in regions with no historical or directly observed eruptions. Geochemical and geophysical techniques are used to study volcano processes at scales ranging from crystals to plumes of volcanic ash. Models reveal essential processes that control volcanic eruptions, and guide data collection. Monitoring provides a wealth of information about the life cycle of volcanoes and vital clues about what kind of eruption is likely and when it may occur.

1.1 OVERVIEW OF THIS REPORT

At the request of managers at the National Aeronautics and Space Administration (NASA), the National Science Foundation, and the U.S. Geological Survey (USGS), the National Academies of Sciences, Engineering, and Medicine established a committee to undertake the following tasks:

• Summarize current understanding of how magma is stored, ascends, and erupts.
• Discuss new disciplinary and interdisciplinary research on volcanic processes and precursors that could lead to forecasts of the type, size, and timing of volcanic eruptions.
• Describe new observations or instrument deployment strategies that could improve quantification of volcanic eruption processes and precursors.
• Identify priority research and observations needed to improve understanding of volcanic eruptions and to inform monitoring and early warning efforts.

The roles of the three agencies in advancing volcano science are summarized in Box 1.1 .

The committee held four meetings, including an international workshop, to gather information, deliberate, and prepare its report. The report is not intended to be a comprehensive review, but rather to provide a broad overview of the topics listed above. Chapter 2 addresses the opportunities for better understanding the storage, ascent, and eruption of magmas. Chapter 3 summarizes the challenges and prospects for forecasting eruptions and their consequences. Chapter 4 highlights repercussions of volcanic eruptions on a host of other Earth systems. Although not explicitly called out in the four tasks, the interactions between volcanoes and other Earth systems affect the consequences of eruptions, and offer opportunities to improve forecasting and obtain new insights into volcanic processes. Chapter 5 summarizes opportunities to strengthen

research in volcano science. Chapter 6 provides overarching conclusions. Supporting material appears in appendixes, including a list of volcano databases (see Appendix A ), a list of workshop participants (see Appendix B ), biographical sketches of the committee members (see Appendix C ), and a list of acronyms and abbreviations (see Appendix D ).

Background information on these topics is summarized in the rest of this chapter.

1.2 VOLCANOES IN THE UNITED STATES

The USGS has identified 169 potentially active volcanoes in the United States and its territories (e.g., Marianas), 55 of which pose a high threat or very high threat ( Ewert et al., 2005 ). Of the total, 84 are monitored by at least one seismometer, and only 3 have gas sensors (as of November 2016). 1 Volcanoes are found in the Cascade mountains, Aleutian arc, Hawaii, and the western interior of the continental United States ( Figure 1.4 ). The geographical extent and eruption hazards of these volcanoes are summarized below.

The Cascade volcanoes extend from Lassen Peak in northern California to Mount Meager in British Columbia. The historical record contains only small- to moderate-sized eruptions, but the geologic record reveals much larger eruptions ( Carey et al., 1995 ; Hildreth, 2007 ). Activity tends to be sporadic ( Figure 1.5 ). For example, nine Cascade eruptions occurred in the 1850s, but none occurred between 1915 and 1980, when Mount St. Helens erupted. Consequently, forecasting eruptions in the Cascades is subject to considerable uncertainty. Over the coming decades, there may be multiple eruptions from several volcanoes or no eruptions at all.

The Aleutian arc extends 2,500 km across the North Pacific and comprises more than 130 active and potentially active volcanoes. Although remote, these volcanoes pose a high risk to overflying aircraft that carry more than 30,000 passengers a day, and are monitored by a combination of ground- and space-based sensors. One or two small to moderate explosive eruptions occur in the Aleutians every year, and very large eruptions occur less frequently. For example, the world’s largest eruption of the 20th century occurred approximately 300 miles from Anchorage, in 1912.

In Hawaii, Kilauea has been erupting largely effusively since 1983, but the location and nature of eruptions can vary dramatically, presenting challenges for disaster preparation. The population at risk from large-volume, rapidly moving lava flows on the flanks of the Mauna Loa volcano has grown tremendously in the past few decades ( Dietterich and Cashman, 2014 ), and few island residents are prepared for the even larger magnitude explosive eruptions that are documented in the last 500 years ( Swanson et al., 2014 ).

All western states have potentially active volcanoes, from New Mexico, where lava flows have reached within a few kilometers of the Texas and Oklahoma borders ( Fitton et al., 1991 ), to Montana, which borders the Yellowstone caldera ( Christiansen, 1984 ). These volcanoes range from immense calderas that formed from super-eruptions ( Mastin et al., 2014 ) to small-volume basaltic volcanic fields that erupt lava flows and tephra for a few months to a few decades. Some of these eruptions are monogenic (erupt just once) and pose a special challenge for forecasting. Rates of activity in these distributed volcanic fields are low, with many eruptions during the past few thousand years (e.g., Dunbar, 1999 ; Fenton, 2012 ; Laughlin et al., 1994 ), but none during the past hundred years.

1.3 THE STRUCTURE OF A VOLCANO

Volcanoes often form prominent landforms, with imposing peaks that tower above the surrounding landscape, large depressions (calderas), or volcanic fields with numerous dispersed cinder cones, shield volcanoes, domes, and lava flows. These various landforms reflect the plate tectonic setting, the ways in which those volcanoes erupt, and the number of eruptions. Volcanic landforms change continuously through the interplay between constructive processes such as eruption and intrusion, and modification by tectonics, climate, and erosion. The stratigraphic and structural architecture of volcanoes yields critical information on eruption history and processes that operate within the volcano.

Beneath the volcano lies a magmatic system that in most cases extends through the crust, except during eruption. Depending on the setting, magmas may rise

___________________

1 Personal communication from Charles Mandeville, Program Coordinator, Volcano Hazards Program, U.S. Geological Survey, on November 26, 2016.

directly from the mantle or be staged in one or more storage regions within the crust before erupting. The uppermost part (within 2–3 km of Earth’s surface) often hosts an active hydrothermal system where meteoric groundwater mingles with magmatic volatiles and is heated by deeper magma. Identifying the extent and vigor of hydrothermal activity is important for three reasons: (1) much of the unrest at volcanoes occurs in hydrothermal systems, and understanding the interaction of hydrothermal and magmatic systems is important for forecasting; (2) pressure buildup can cause sudden and potentially deadly phreatic explosions from the hydrothermal system itself (such as on Ontake, Japan, in 2014), which, in turn, can influence the deeper magmatic system; and (3) hydrothermal systems are energy resources and create ore deposits.

Below the hydrothermal system lies a magma reservoir where magma accumulates and evolves prior to eruption. Although traditionally modeled as a fluid-filled cavity, there is growing evidence that magma reservoirs may comprise an interconnected complex of vertical and/or horizontal magma-filled cracks, or a partially molten mush zone, or interleaved lenses of magma and solid material ( Cashman and Giordano, 2014 ). In arc volcanoes, magma chambers are typically located 3–6 km below the surface. The magma chamber is usually connected to the surface via a fluid-filled conduit only during eruptions. In some settings, magma may ascend directly from the mantle without being stored in the crust.

In the broadest sense, long-lived magma reservoirs comprise both eruptible magma (often assumed to contain less than about 50 percent crystals) and an accumulation of crystals that grow along the margins or settle to the bottom of the magma chamber. Physical segregation of dense crystals and metals can cause the floor of the magma chamber to sag, a process balanced by upward migration of more buoyant melt. A long-lived magma chamber can thus become increasingly stratified in composition and density.

The deepest structure beneath volcanoes is less well constrained. Swarms of low-frequency earthquakes at mid- to lower-crustal depths (10–40 km) beneath volcanoes suggest that fluid is periodically transferred into the base of the crust ( Power et al., 2004 ). Tomographic studies reveal that active volcanic systems have deep crustal roots that contain, on average, a small fraction of melt, typically less than 10 percent. The spatial distribution of that melt fraction, particularly how much is concentrated in lenses or in larger magma bodies, is unknown. Erupted samples preserve petrologic and geochemical evidence of deep crystallization, which requires some degree of melt accumulation. Seismic imaging and sparse outcrops suggest that the proportion of unerupted solidified magma relative to the surrounding country rock increases with depth and that the deep roots of volcanoes are much more extensive than their surface expression.

1.4 MONITORING VOLCANOES

Volcano monitoring is critical for hazard forecasts, eruption forecasts, and risk mitigation. However, many volcanoes are not monitored at all, and others are monitored using only a few types of instruments. Some parameters, such as the mass, extent, and trajectory of a volcanic ash cloud, are more effectively measured by satellites. Other parameters, notably low-magnitude earthquakes and volcanic gas emissions that may signal an impending eruption, require ground-based monitoring on or close to the volcanic edifice. This section summarizes existing and emerging technologies for monitoring volcanoes from the ground and from space.

Monitoring Volcanoes on or Near the Ground

Ground-based monitoring provides data on the location and movement of magma. To adequately capture what is happening inside a volcano, it is necessary to obtain a long-term and continuous record, with periods spanning both volcanic quiescence and periods of unrest. High-frequency data sampling and efficient near-real-time relay of information are important, especially when processes within the volcano–magmatic–hydrothermal system are changing rapidly. Many ground-based field campaigns are time intensive and can be hazardous when volcanoes are active. In these situations, telemetry systems permit the safe and continuous collection of data, although the conditions can be harsh and the lifetime of instruments can be limited in these conditions.

Ground-based volcano monitoring falls into four broad categories: seismic, deformation, gas, and thermal monitoring ( Table 1.1 ). Seismic monitoring tools,

TABLE 1.1 Ground-Based Instrumentation for Monitoring Volcanoes

including seismometers and infrasound sensors, are used to detect vibrations caused by breakage of rock and movement of fluids and to assess the evolution of eruptive activity. Ambient seismic noise monitoring can image subsurface reservoirs and document changes in wave speed that may reflect stress. changes. Deformation monitoring tools, including tiltmeters, borehole strainmeters, the Global Navigation Satellite System (GNSS, which includes the Global Positioning System [GPS]), lidar, radar, and gravimeters, are used to detect the motion of magma and other fluids in the subsurface. Some of these tools, such as GNSS and lidar, are also used to detect erupted products, including ash clouds, pyroclastic density currents, and volcanic bombs. Gas monitoring tools, including a range of sensors ( Table 1.1 ), and direct sampling of gases and fluids are used to detect magma intrusions and changes in magma–hydrothermal interactions. Thermal monitoring tools, such as infrared cameras, are used to detect dome growth and lava breakouts. Continuous video or photographic observations are also commonly used and, despite their simplicity, most directly document volcanic activity. Less commonly used monitoring technologies, such as self-potential, electromagnetic techniques, and lightning detection are used to constrain fluid movement and to detect

ash clouds. In addition, unmanned aerial vehicles (e.g., aircraft and drones) are increasingly being used to collect data. Rapid sample collection and analysis is also becoming more common as a monitoring tool at volcano observatories. A schematic of ground-based monitoring techniques is shown in Figure 1.6 .

Monitoring Volcanoes from Space

Satellite-borne sensors and instruments provide synoptic observations during volcanic eruptions when collecting data from the ground is too hazardous or where volcanoes are too remote for regular observation. Repeat-pass data collected over years or decades provide a powerful means for detecting surface changes on active volcanoes. Improvements in instrument sensitivity, data availability, and the computational capacity required to process large volumes of data have led to a dramatic increase in “satellite volcano science.”

Although no satellite-borne sensor currently in orbit has been specifically designed for volcano monitoring, a number of sensors measure volcano-relevant

TABLE 1.2 Satellite-Borne Sensor Suite for Volcano Monitoring

NOTE: AIRS, Atmospheric Infrared Sounder; ALOS, Advanced Land Observing Satellite; ASTER, Advanced Spaceborne Thermal Emission and Reflection Radiometer; AVHRR, Advanced Very High Resolution Radiometer; CALIPSO, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation; COSMO-SkyMed, Constellation of Small Satellites for Mediterranean Basin Observation; GOES, Geostationary Operational Environmental Satellite; IASI, Infrared Atmospheric Sounding Interferometer; MISR, Multi-angle Imaging SpectroRadiometer; MLS, Microwave Limb Sounder; MODIS, Moderate Resolution Imaging Spectroradiometer; OMI, Ozone Monitoring Instrument; OMPS, Ozone Mapping and Profiler Suite; SAGE, Stratospheric Aerosol and Gas Experiment.

parameters, including heat flux, gas and ash emissions, and deformation ( Table 1.2 ). Thermal infrared data are used to detect eruption onset and cessation, calculate lava effusion rates, map lava flows, and estimate ash column heights during explosive eruptions. In some cases, satellites may capture thermal precursors to eruptions, although low-temperature phenomena are challenging to detect. Both high-temporal/low-spatial-resolution (geostationary orbit) and high-spatial/low-temporal-resolution (polar orbit) thermal infrared observations are needed for global volcano monitoring.

Satellite-borne sensors are particularly effective for observing the emission and dispersion of volcanic gas and ash plumes in the atmosphere. Although several volcanic gas species can be detected from space (including SO 2 , BrO, OClO, H 2 S, HCl, and CO; Carn et al., 2016 ), SO 2 is the most readily measured, and it is also responsible for much of the impact of eruptions on climate. Satellite measurements of SO 2 are valuable for detecting eruptions, estimating global volcanic fluxes and recycling of other volatile species, and tracking volcanic clouds that may be hazardous to aviation in near real time. Volcanic ash cloud altitude is most accurately determined by spaceborne lidar, although spatial coverage is limited. Techniques for measuring volcanic CO 2 from space are under development and could lead to earlier detection of preeruptive volcanic degassing.

Interferometric synthetic aperture radar (InSAR) enables global-scale background monitoring of volcano deformation ( Figure 1.7 ). InSAR provides much higher spatial resolution than GPS, but lower accuracy and temporal resolution. However, orbit repeat times will diminish as more InSAR missions are launched, such as the European Space Agency’s recently deployed Sentinel-1 satellite and the NASA–Indian Space Research Organisation synthetic aperture radar mission planned for launch in 2020.

1.5 ERUPTION BEHAVIOR

Eruptions range from violently explosive to gently effusive, from short lived (hours to days) to persistent over decades or centuries, from sustained to intermittent, and from steady to unsteady ( Siebert et al., 2015 ). Eruptions may initiate from processes within the magmatic system ( Section 1.3 ) or be triggered by processes and properties external to the volcano, such as precipitation, landslides, and earthquakes. The eruption behavior of a volcano may change over time. No classification scheme captures this full diversity of behaviors (see Bonadonna et al., 2016 ), but some common schemes to describe the style, magnitude, and intensity of eruptions are summarized below.

Eruption Magnitude and Intensity

The size of eruptions is usually described in terms of total erupted mass (or volume), often referred to as magnitude, and mass eruption rate, often referred to as intensity. Pyle (2015) quantified magnitude and eruption intensity as follows:

magnitude = log 10 (mass, in kg) – 7, and

intensity = log 10 (mass eruption rate, in kg/s) + 3.

The Volcano Explosivity Index (VEI) introduced by Newhall and Self (1982) assigns eruptions to a VEI class based primarily on measures of either magnitude (erupted mass or volume) or intensity (mass eruption rate and/or eruption plume height), with more weight given to magnitude. The VEI classes are summarized in Figure 1.8 . The VEI classification is still in use, despite its many limitations, such as its reliance on only a few types of measurements and its poor fit for small to moderate eruptions (see Bonadonna et al., 2016 ).

Smaller VEI events are relatively common, whereas larger VEI events are exponentially less frequent ( Siebert et al., 2015 ). For example, on average about three VEI 3 eruptions occur each year, whereas there is a 5 percent chance of a VEI 5 eruption and a 0.2 percent chance of a VEI 7 (e.g., Crater Lake, Oregon) event in any year.

Eruption Style

The style of an eruption encompasses factors such as eruption duration and steadiness, magnitude, gas flux, fountain or column height, and involvement of magma and/or external source of water (phreatic and phreatomagmatic eruptions). Eruptions are first divided into effusive (lava producing) and explosive (pyroclast producing) styles, although individual eruptions can be simultaneously effusive and weakly explosive, and can pass rapidly and repeatedly between eruption styles. Explosive eruptions are further subdivided into styles that are sustained on time scales of hours to days and styles that are short lived ( Table 1.3 ).

Classification of eruption style is often qualitative and based on historical accounts of characteristic eruptions from type-volcanoes. However, many type-volcanoes exhibit a range of eruption styles over time (e.g., progressing between Strombolian, Vulcanian, and Plinian behavior; see Fee et al., 2010 ), which has given rise to terms such as subplinian or violent Strombolian.

1.6 ERUPTION HAZARDS

Eruption hazards are diverse ( Figure 1.9 ) and may extend more than thousands of kilometers from an active volcano. From the perspective of risk and impact, it is useful to distinguish between near-source and distal hazards. Near-source hazards are far more unpredictable than distal hazards.

Near-source hazards include those that are airborne, such as tephra fallout, volcanic gases, and volcanic projectiles, and those that are transported laterally on or near the ground surface, such as pyroclastic density currents, lava flows, and lahars. Pyroclastic density currents are hot volcanic flows containing mixtures of gas and micron- to meter-sized volcanic particles. They can travel at velocities exceeding 100 km per hour. The heat combined with the high density of material within these flows obliterates objects in their path, making them the most destructive of volcanic hazards. Lava flows also destroy everything in their path, but usually move slowly enough to allow people to get out of the way. Lahars are mixtures of volcanic debris, sediment, and water that can travel many tens of kilometers along valleys and river channels. They may be triggered during an eruption by interaction between volcanic prod-

TABLE 1.3 Characteristics of Different Eruption Styles

ucts and snow, ice, rain, or groundwater. Lahars can be more devastating than the eruption itself. Ballistic blocks are large projectiles that typically fall within 1–5 km from vents.

The largest eruptions create distal hazards. Explosive eruptions produce plumes that are capable of dispersing ash hundreds to thousands of kilometers from the volcano. The thickness of ash deposited depends on the intensity and duration of the eruption and the wind direction. Airborne ash and ash fall are the most severe distal hazards and are likely to affect many more people than near-source hazards. They cause respiratory problems and roof collapse, and also affect transport networks and infrastructure needed to support emergency response. Volcanic ash is a serious risk to air traffic. Several jets fully loaded with passengers have temporarily lost power on all engines after encountering dilute ash clouds (e.g., Guffanti et al., 2010 ). Large lava flows, such as the 1783 Laki eruption in Iceland, emit volcanic gases that create respiratory problems and acidic rain more than 1,000 km from the eruption. Observed impacts of basaltic eruptions in Hawaii and Iceland include regional volcanic haze (“vog”) and acid rain that affect both agriculture and human health (e.g., Thordarson and Self, 2003 ) and fluorine can contaminate grazing land and water supplies (e.g., Cronin et al., 2003 ). Diffuse degassing of CO 2 can lead to deadly concentrations with fatal consequences such as occurred at Mammoth Lakes, California, or cause lakes to erupt, leading to massive CO 2 releases that suffocate people (e.g., Lake Nyos, Cameroon).

Secondary hazards can be more devastating than the initial eruption. Examples include lahars initiated by storms, earthquakes, landslides, and tsunamis from eruptions or flank collapse; volcanic ash remobilized by wind to affect human health and aviation for extended periods of time; and flooding because rain can no longer infiltrate the ground.

1.7 MODELING VOLCANIC ERUPTIONS

Volcanic processes are governed by the laws of mass, momentum, and energy conservation. It is possible to develop models for magmatic and volcanic phenomena based on these laws, given sufficient information on mechanical and thermodynamic properties of the different components and how they interact with each other. Models are being developed for all processes in volcanic systems, including melt transport in the mantle, the evolution of magma bodies within the crust, the ascent of magmas to the surface, and the fate of magma that erupts effusively or explosively.

A central challenge for developing models is that volcanic eruptions are complex multiphase and multicomponent systems that involve interacting processes over a wide range of length and time scales. For example, during storage and ascent, the composition, temperature, and physical properties of magma and host rocks evolve. Bubbles and crystals nucleate and grow in this magma and, in turn, greatly influence the properties of the magmas and lavas. In explosive eruptions, magma fragmentation creates a hot mixture of gas and particles with a wide range of sizes and densities. Magma also interacts with its surroundings: the deformable rocks that surround the magma chamber and conduit, the potentially volatile groundwater and surface water, a changing landscape over which pyroclastic density currents and lava flows travel, and the atmosphere through which eruption columns rise.

Models for volcanic phenomena that involve a small number of processes and that are relatively amenable to direct observation, such as volcanic plumes, are relatively straightforward to develop and test. In contrast, phenomena that occur underground are more difficult to model because there are more interacting processes. In those cases, direct validation is much more challenging and in many cases impossible. Forecasting ash dispersal using plume models is more straightforward and testable than forecasting the onset, duration, and style of eruption using models that seek to explain geophysical and geochemical precursors. In all cases, however, the use of even imperfect models helps improve the understanding of volcanic systems.

Modeling approaches can be divided into three categories:

• Reduced models make simplifying assumptions about dynamics, heat transfer, and geometry to develop first-order explanations for key properties and processes, such as the velocity of lava flows and pyroclastic density currents, the height of eruption columns, the magma chamber size and depth, the dispersal of tephra, and the ascent of magma in conduits. Well-calibrated or tested reduced models offer a straightforward ap-

proach for combining observations and models in real time in an operational setting (e.g., ash dispersal forecasting for aviation safety). Models may not need to be complex if they capture the most important processes, although simplifications require testing against more comprehensive models and observations.

• Multiphase and multiphysics models improve scientific understanding of complex processes by invoking fewer assumptions and idealizations than reduced models ( Figure 1.10 ), but at the expense of increased complexity and computational demands. They also require additional components, such as a model for how magma in magma chambers and conduits deforms when stressed; a model for turbulence in pyroclastic density currents and plumes; terms that describe the thermal and mechanical exchange among gases, crystals, and particles; and a description of ash aggregation in eruption columns. A central challenge for multiphysics models is integrating small-scale processes with large-scale dynamics. Many of the models used in volcano science build on understanding developed in other science and engineering fields and for other ap-

plications. Multiphysics and multiscale models benefit from rapidly expanding computational capabilities.

• Laboratory experiments simulate processes for which the geometry and physical and thermal processes and properties can be scaled ( Mader et al., 2004 ). Such experiments provide insights on fundamental processes, such as crystal dynamics in flowing magmas, entrainment in eruption columns, propagation of dikes, and sedimentation from pyroclastic density currents ( Figure 1.11 ). Experiments have also been used successfully to develop the subsystem models used in numerical simulations, and to validate computer simulations for known inputs and properties.

The great diversity of existing models reflects to a large extent the many interacting processes that operate in volcanic eruptions and the corresponding simplifying assumptions currently required to construct such models. The challenge in developing models is often highlighted in discrepancies between models and observations of natural systems. Nevertheless, eruption models reveal essential processes governing volcanic eruptions, and they provide a basis for interpreting measurements from prehistoric and active eruptions and for closing observational gaps. Mathematical models offer a guide for what observations will be most useful. They may also be used to make quantitative and testable predictions, supporting forecasting and hazard assessment.

Volcanic eruptions are common, with more than 50 volcanic eruptions in the United States alone in the past 31 years. These eruptions can have devastating economic and social consequences, even at great distances from the volcano. Fortunately many eruptions are preceded by unrest that can be detected using ground, airborne, and spaceborne instruments. Data from these instruments, combined with basic understanding of how volcanoes work, form the basis for forecasting eruptions—where, when, how big, how long, and the consequences.

Accurate forecasts of the likelihood and magnitude of an eruption in a specified timeframe are rooted in a scientific understanding of the processes that govern the storage, ascent, and eruption of magma. Yet our understanding of volcanic systems is incomplete and biased by the limited number of volcanoes and eruption styles observed with advanced instrumentation. Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing identifies key science questions, research and observation priorities, and approaches for building a volcano science community capable of tackling them. This report presents goals for making major advances in volcano science.

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• Review Article
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• Published: 12 February 2021

A review framework of how earthquakes trigger volcanic eruptions

• Gilles Seropian   ORCID: orcid.org/0000-0002-1885-4763 1 ,
• Ben M. Kennedy   ORCID: orcid.org/0000-0001-7235-6493 1 ,
• Thomas R. Walter 2 ,
• Mie Ichihara 3 &
• Arthur D. Jolly 4  

Nature Communications volume  12 , Article number:  1004 ( 2021 ) Cite this article

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• Volcanology

It is generally accepted that tectonic earthquakes may trigger volcanic activity, although the underlying mechanisms are poorly constrained. Here, we review current knowledge, and introduce a novel framework to help characterize earthquake-triggering processes. This framework outlines three parameters observable at volcanoes, namely magma viscosity, open- or closed-system degassing and the presence or absence of an active hydrothermal system. Our classification illustrates that most types of volcanoes may be seismically-triggered, though require different combinations of volcanic and seismic conditions, and triggering is unlikely unless the system is primed for eruption. Seismically-triggered unrest is more common, and particularly associated with hydrothermal systems.

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Introduction.

Volcanic eruptions and earthquakes are amongst the most spectacular and sometimes deadliest natural events occurring on our planet, fascinating humans for centuries, with records extending to ancient times 1 , 2 , 3 . One naturally arising question is whether tectonic earthquakes can trigger volcanic eruptions, referred to as earthquake–volcano interactions 4 or seismically triggered eruptions 5 , 6 . The statistical record of seismically triggered eruptions shows it is a relatively rare occurrence 7 , 8 , but understanding the causal relationships between earthquakes and volcanoes is essential towards more efficient hazard management approaches. A number of articles have summarized recent concepts and observations of earthquake–volcano interactions, including Hill et al. 4 , Koyama 9 , Manga and Brodsky 6 , Eggert and Walter 10 and Watt et al. 11 . We herein provide a framework for using their findings and highlight recent advances. Our motivation is to identify which types of volcanoes are more susceptible to seismic triggers.

Volcanoes display an immense diversity in subsurface and aerial structure, style of eruption, chemical composition or precursory signals. As a result, the underlying seismic-triggering mechanisms may vary from one seismically triggered eruption to another. Latter 12 already noted in 1971 that “the process is neither universal nor invariable”. Besides, earthquakes may even inhibit volcanic activity in some conditions 9 , 13 , 14 , 15 . Hence, can we identify and classify volcanoes based on their sensitivity to seismic-triggering mechanisms? A common method is to devise a classification of volcanoes based on historical records: if a given type of volcano erupts more frequently after earthquakes, then it is considered more sensitive 8 , 9 , 16 , 17 . Unfortunately, the limited number of recorded events precludes statistically significant correlations for most volcanoes 8 .

In this contribution, we adopt a new strategy where we start from the underlying physical mechanisms in order to derive our classification. By considering the favourable conditions for each mechanism, we construct a series of different volcano types, with each one being sensitive to different mechanisms. We then examine different earthquake scenarios and the control they exert on triggering dynamics. We thus produce a novel classification of volcanoes, according to how they can be seismically triggered aimed at informing future monitoring or statistical efforts.

Observations

The oldest and commonest evidence of earthquake–volcano interactions is serendipitous observation 18 , 19 , 20 , 21 . These potentially coincidental observations later evolved into accurate records combining multiple geophysical signals 10 , permitting more precise correlations 22 , 23 , 24 , 25 . In particular, the recent emergence of satellite monitoring as a reliable tool in geosciences allowed for a more systematic and consistent monitoring of volcanoes globally 17 , 26 , 27 , 28 . The influence of an earthquake on an eruption can also be inferred a posteriori from crystal textures 29 , 30 , 31 . Like other authors, we emphasize that a spatio-temporal correlation between seismic and volcanic events does not necessarily imply a causal relationship. Two concurrent events could result from a common third underlying process, or occur by chance. Yet observing a correlation is a necessary first step in unravelling a potential causal relationship.

There are documented cases of both changes from quiescence to eruption 6 , 20 , 29 , 32 , 33 , 34 , 35 , and changes in style of an ongoing eruption 36 , 37 , 38 , 39 , 40 in the weeks following an earthquake. Earthquakes may also trigger a broad spectrum of non-eruptive unrest phenomena including increased seismicity 25 , 41 , 42 , 43 , 44 , 45 , degassing 17 , 25 , 34 , 46 , 47 , heat flux 26 , 27 , 28 , 48 or subsidence 49 , 50 . Hydrothermal systems are particularly sensitive to seismic stimuli, with many reports of increased activity following earthquakes 6 , 51 , 52 , 53 , 54 , 55 .

Statistical inference

Statistical tests are a crucial step to assess whether eruptions follow earthquakes due to significant coupling or simply by coincidence. Determining the temporal and spatial extent of earthquakes’ impact on volcanoes also helps to constrain plausible mechanisms and inform hazard models. The historical earthquake and eruption records are regarded to be complete only in the most recent period (1960s–present) 8 , 56 . As a result, the sample size (i.e. number of events considered) is quite small, decreasing the robustness of statistical tests.

The early statistical groundwork on a global scale 5 , 6 , 10 , 56 , 57 was updated by Sawi and Manga 8 who conclude that the apparent correlations within a few days occur most likely due to chance. Yet, there exists a slight but significant increase in eruption rate in the 2–5 years period following an earthquake on a global scale 8 , 33 , 56 . Statistical tests perform better on regional scales, in particular in active subduction zones 8 , 10 . This is supported by detailed studies of the Chilean 11 , 16 , Japanese 58 and Indonesian 7 , 33 subduction zones which all show increased eruption rates—to various degrees—following large magnitude earthquakes. Ultimately, the internal state of the volcano—whether it is “ready” to erupt—dictates whether it will be seismically triggered or not 7 . This association may thus simply reflect the fact that subduction zones feature the highest concentration of large earthquakes and volcanoes on the verge of erupting 7 .

The maximum distance at which eruptions may be seismically triggered is debated. Delle Donne et al. 27 propose a distance–magnitude relationship, akin to what is found in the mud volcanism and soil liquefaction literature 59 , 60 . For triggered-eruptions stricto sensu, Nishimura 56 suggests a limit of about 200 km from the epicentre, whereas Marzocchi et al. 61 propose 1000 km. Concerning triggered-unrest, earthquake-induced thermal anomalies 27 , 28 and seismicity 62 are both reported at distances over 10,000 km. This matches observations of seismically induced changes in groundwater level or streamflow 63 .

Triggering mechanisms

A wide range of triggering mechanisms have been proposed, affecting the host rock, magma chamber and/or hydrothermal system, causing stress changes in solid state and dynamic variations in fluid and multiphase systems 4 , 6 , 9 , 64 . Earthquakes result from sudden ruptures in the crust, and cause significant changes in the surrounding stress field. We must thus investigate how stress perturbations affect magmatic systems in order to understand how this may eventually lead to an eruption. Stress can be transferred either statically or dynamically (Fig.  1 ), which will in turn dictate what triggering mechanisms can occur. We now examine both cases.

Dynamic stresses are transient, whereas static stresses last permanently. a In the region close to the epicentre, dynamic and static stresses have similar amplitudes. b Far from the epicentre, however, dynamic stresses have a much larger amplitude and static stresses are negligible.

Static processes

Static stress changes result from the deformation of rocks following an earthquake 65 (Fig.  1 ). The resultant strain is spatially confined to within a few fault lengths around the epicentre and remains until the stress is elastically released or dissipated by ductile flow. Static stress changes can be either compressive or extensional, both of which might promote eruption 9 , 56 .

Extensional stresses facilitate dyke opening by “unclamping” the system (Fig.  2 ), thus promoting magma transport and potentially triggering an eruption 16 , 29 , 32 , 33 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 . If the magma already contains bubbles, then reduced compression could result in overpressure 76 , 77 . Additionally, extension favours strike-slip faulting and increased permeability 78 , 79 , thus allowing increased advection of magmatic fluids and melt 15 , 78 .

Mechanisms names in yellow are due to static stresses whereas those in black and white arise from dynamic stresses.

Compressional stresses have been conceptualized to squeeze magma upwards 13 , 66 , 67 , 80 , 81 , 82 , 83 (Fig.  2 ), though this process has been criticized 84 . Conversely, compression at shallow depths has been inferred to inhibit and arrest dyke propagation 9 , 14 , 85 , 86 , 87 , and thus prevent eruption. We emphasize that the orientation of volcanic structures relative to stresses is critical to these models.

Seismic stresses are eventually dissipated by viscous flow of the lower lithosphere and asthenosphere 88 , 89 . This process happens over years to decades. This slow relaxation of underlying layers will impose “quasi-static” stress changes on the overlying, brittle lithosphere. These quasi-static stress changes have also been postulated to favour volcanic eruptions 4 , 61 , though the physical mechanism(s) require further study.

Dynamic processes

Dynamic stresses involve the oscillatory stresses induced by seismic waves 90 (Fig.  1 ). The amplitudes of dynamic stresses decrease much more gradually with distance than their static counterparts, hence dynamic stresses will generally (1) be greater and (2) travel much further than static stresses 6 , 90 , 91 , 92 . However, dynamic stresses are oscillatory phenomena, and thus feature a range of characteristic frequencies and are transient. Responses to dynamic stresses can be broadly divided into three categories.

Volatile processes

Volatiles have the lowest viscosities of all volcanic fluids (as low as 10 −5  Pa.s), high compressibility, and can thus respond quickly to dynamic stresses. Three mechanisms associated with volatiles could lead to an eruption, namely (1) bubble nucleation and growth, (2) advective overpressure associated with bubble rise and (3) falling crystal roofs facilitating vesiculation (Fig.  2 ).

Dynamic stresses could induce bubble nucleation in magmas 6 , 23 by varying the local pressure. The phenomenon is well known in other fluids, in particular in water 93 , and usually referred to as cavitation. Static decompression may sometimes be sufficient to trigger nucleation 23 , 33 , 35 . Pressure oscillations in the fluid can locally change the solubility and diffusivity of volatiles (mostly water), thus accelerating bubble formation processes. The phenomenon was experimentally demonstrated for groundwater 94 . Bubble nucleation in magma, however, is a very complex process, depending upon many parameters 95 (e.g., volatile oversaturation, melt composition, presence of nucleation sites). For instance, it is notoriously difficult to nucleate bubbles experimentally in crystal poor rhyolite 96 , sometimes requiring immense pressure drops >100 MPa, much larger than seismic dynamic stresses 6 , 90 (generally <10 MPa). With abundant nucleation sites, however, a few MPa may be sufficient to induce bubble nucleation 97 , 98 . To the best of our knowledge, there is no available experimental evidence showing that pressure oscillations can induce bubble nucleation in silicate melts.

Magma often already contains bubbles, in which case problems related to nucleation become irrelevant. Dynamic stresses may then accelerate volatile diffusion and bubble growth. Rectified diffusion is a very commonly cited mechanism where seismic waves enhance diffusion of volatiles inside the bubbles 99 , 100 , 101 but its effects have initially been overestimated, and it is now considered most likely inefficient in magma 6 , 102 . We will then not consider rectified diffusion further in this contribution. Other dynamic mechanisms that could facilitate bubble growth and coalescence include Ostwald ripening 103 , 104 or advection due to Bjerknes force 105 , but they have not been considered under the lens of earthquake–volcano interactions yet.

A further mechanism related to bubbles is advective overpressure 106 , 107 (Fig.  2 ). Here, it is considered that bubbles that were previously held down to the reservoir floor or walls by surface tension can be shaken loose by seismic waves. Assuming an incompressible fluid, a closed system with undeformable walls and no mass exchange between the bubbles and the melt, the bubbles can carry large overpressures with them while rising 106 , 108 , 109 . Nevertheless, this mechanism has been heavily debated 110 , 111 because most of the assumptions are unrealistic for a magmatic reservoir. Advective overpressure could still be effective in hydrothermal and hydrogeological systems however 53 , 54 , 107 , 112 . It is also possible that seismic waves increase bubble rise ascent speed, as shown by preliminary results from analogue experiments in shear thinning fluids 113 , 114 .

Finally, seismic waves could dislodge crystal aggregates that accumulate on top of a magma reservoir 4 , 6 (Fig.  2 ). Upon detaching, dense crystals will sink and lighter melt will rise to replace them. Upwelling melt is then prone to vesiculation, which could in turn lead to an eruption. Preliminary calculations 4 , 6 showed the mechanism to be theoretically realistic, but it will require further work to demonstrate that (a) these crystal roofs exist, (b) characterize their rheology and (c) validate the theory used to describe sinking of crystal plumes.

Resonance processes

The second category of mechanisms relates to the mechanical sway of magma in response to shaking. The amount of movement will depend on a number of parameters, including the resonant frequency of the system, mainly controlled by the edifice dimensions and reservoir geometry. If the seismic waves match this frequency, the processes will be greatly enhanced; otherwise effects will be negligible. Two resonance mechanisms have been proposed, namely sloshing and edifice resonance (Fig.  2 ).

Seismic waves can induce sloshing in the reservoir 115 . Sloshing refers to the movement of a fluid inside its container 116 , 117 , 118 —here magma in its reservoir. Sloshing of a foam layer in a magmatic reservoir or conduit could lead to foam collapse, increased degassing and vesiculation, potentially forming gas slugs and Strombolian eruptions 115 . Analogue experiments show that foam collapse will only occur if (1) the incident seismic waves carry significant energy around the reservoir’s resonance frequency to initiate sloshing and (2) a magma foam is present with a free top surface or is overlying a deeper dense melt region 115 . The mechanism will further be facilitated by a foam featuring a high bubble fraction, large bubbles and low melt viscosity.

Seismic waves can also increase melt and volatile migration inside a volcanic edifice 119 . A combination of analogue and numerical models show that shaking will accelerate fluid movement in either direction (upwards, downwards or laterally) depending upon the fluid buoyancy and storage depth 119 . Lighter (in particular bubble rich) and shallower fluids will tend to move upwards. The phenomenon is again greatly enhanced when the seismic waves resonate with the edifice. Thus, edifice resonance may either favour eruption by facilitating magma mobilization upwards or retard an eruption by forcing magma downwards 119 .

Hydrothermal system triggering

Hydrothermal and geothermal systems have been observed to be extremely sensitive to earthquakes and dynamic stresses in particular 6 , 15 , 41 , 51 , 52 , 54 , 90 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 . Hydrothermal systems are also generally well connected to the underlying magmatic reservoir 133 , 134 , hence destabilization may lead to a top-down depressurization of the entire magmatic system, and eventually magmatic eruption 4 , 15 , 135 , 136 , 137 , 138 (Fig.  2 ). The possibility for hydrothermal systems to form a link between seismic waves and magmatic reservoir destabilization has received little attention under the lens of seismic triggers 4 , 83 , 138 but observations 15 , 34 , 42 , 127 suggest that it could play a major role. The triggering mechanisms of hydrothermal systems generally fall into two categories: change in fluid pressure and change in permeability.

The physical models describing changes in fluid pressure in hydrothermal systems are similar to the ones described in section “Volatile processes”. The main mechanisms are bubble nucleation 94 and advective overpressure 54 , 107 , 112 . Here, however, the main fluid is water, with a viscosity of 10 −3  Pa.s. Additionally, the gas phase is generated by evaporation instead of volatile diffusion in the liquid phase. These features allow for much faster kinetics and less viscous dissipation, making these mechanisms more efficient in hydrothermal settings.

Seismic waves can significantly alter permeability over short time-intervals 59 , 139 (Fig.  2 ). Such changes have been particularly well observed in hydrogeologic systems 140 , with sudden variations in streamflow 141 , 142 , groundwater level 143 , 144 , 145 , 146 , 147 , temperature 148 , 149 , 150 and seismically triggered mud volcanism 6 , 60 , 151 , 152 , 153 . With increased permeability, regions of higher and lower pressures may become connected, allowing fluid flow and pore pressure redistribution 59 , 63 . The sudden influx of fluids into originally low-pressure zones, may push such regions beyond a critical pressure threshold and produce an eruption 120 . On the other hand, reduced permeability allows local pressurization, which may lead to fragmentation and eruption 154 , 155 . The mechanisms described hereafter are particularly attractive because they necessitate relatively small (<1 MPa) dynamic stresses, and may thus be triggered more easily 59 . Three mechanisms are often invoked to explain changes in permeability.

Firstly, seismic waves may unclog or clog fractures 156 , 157 , 158 , 159 , 160 . The passage of seismic waves may intensify fluid flow, which could in turn entrain small particulates resulting in both clogging 160 and unclogging 156 downstream depending on fracture orientations.

Dynamic stresses may also enhance or reduce permeability by opening, closing or shearing cracks 15 , 132 , 141 , 161 , 162 , 163 . Opening new cracks or widening already existing ones increases permeability whereas other fractures with less favourable orientations would be closed and hence decrease permeability.

Finally, seismic waves may lower the brittle-plastic transition between the hydrothermal and magmatic systems 4 , 137 (Fig.  2 ). For this scenario, we assume that there exists an impermeable plastic transition zone underlying the hydrothermal system retaining pressurized fluids 164 . In this case, the strain rates imposed by seismic waves may be sufficient to promote brittle behaviour and release overpressurized fluids into the hydrothermal system (referred to as a hydraulic surge 4 ), favouring unrest and eruption 4 , 137 .

External triggers

Earthquakes can also trigger eruptions indirectly via external triggers. These occur when an earthquake triggers a non-volcanic event which then cascades towards an eruption. A typical example is that of an earthquake triggering a landslide or block and ash flow above a critically pressured magmatic reservoir or dome 165 , 166 , 167 . The resulting sudden decompression may lead to eruption of magma. Another documented external trigger is via crust decarbonation 40 . Earthquakes induce cracking in the crust underlying the magmatic reservoir, thus releasing important volumes of CO 2 . CO 2 then flushes the reservoir, significantly lowering the solubility of water, hence triggering vesiculation, pressurization and eventually producing the observed changes in eruption style. While it is important to explore the possible feedbacks between magmatic systems and their environments, we will not consider external triggers further, and solely focus on direct interactions between earthquakes and magmatic systems.

External triggers hence have the potential to trigger eruptions in many possible ways, it is thus important to explore, in the future, the possible feedbacks between an igneous system, its hydrothermal and their mechanical environment when subjected to an earthquake.

Volcano types

For each mechanism, there is a set of favourable physical parameters maximizing triggering efficiency. They can be divided in two categories: (1) volcanic (e.g. melt viscosity) and (2) seismic (e.g. seismic wave frequency). We examine volcanic parameters first.

Our choice of parameters is developed by capturing both the important complexity associated with the mechanisms whilst remaining simple enough to be applied. From section “Triggering mechanisms”, we see that two parameters, namely magma viscosity and whether the system is open or closed, play critical roles for many mechanisms. The sensitivity of hydrothermal systems make them the key third parameter to be. It is interesting to note that this choice of parameters which naturally arises from our analysis resembles other recent volcano classifications 168 , 169 , despite the different objectives. Our classification currently focuses on subaerial volcanism only. Seismic events do trigger various responses from submarine volcanoes 33 , 170 , 171 , 172 ; however, the current amount of available data are too scarce to be fitted in our classification.

The first parameter is magma viscosity, for which we will consider two limiting cases, namely low and high viscosity. Low viscosities generally correspond to basaltic, crystal poor magma, and are lower than or equal to ~10 4  Pa.s 173 , 174 . We delineate high viscosities as greater than or equal to ~10 5  Pa.s and can be achieved by rhyolitic melt, or through the addition of suspended crystals and bubbles 175 , 176 . Other parameters such as water content or temperature also exert significant control on viscosity. This simplified classification does overlook some major rheological properties (e.g. non-Newtonian behaviour 177 , 178 ) yet captures the magma properties that favour certain mechanisms. For instance, it is very unlikely for a magma with viscosity 10 5  Pa.s to ever experience sloshing, but one with viscosity 10 1  Pa.s will.

The second parameter is whether the system is open or closed to degassing. Open systems are permeable and volatiles can easily escape as bubbles, directly out of magma or through fractures. In contrast, in a closed system, permeability is low and volatiles are trapped and cannot leave. It is quite rare for a volcano to display pure open- or closed-system degassing, yet end members are observed in nature for both cases. Lava lakes or Strombolian-style volcanoes are typical examples of open systems. Many very explosive eruptions show a phase of closed-system degassing with low levels of degassing prior to eruption 169 . It is very common for volcanoes to transition from open to closed through time, and even within a single eruptive phase, via a wide range of processes 154 , 179 , 180 , 181 , 182 , 183 . It is key to note that our definition of open and closed systems relates to shallow volatile-controlling conditions and differ from many petrological studies which refer to the connection between deep magma sources and shallow systems.

The third volcanic parameter considered is the presence of an active hydrothermal system. Arguably every volcano features a hydrothermal system; however, we define distinct end members of how well developed the hydrothermal system is. Some volcanoes display clear, persistent hydrothermal surface activity—e.g. acidic crater lakes, and fumaroles—whereas others show barely any visual sign of activity. For instance, it is quite common for smaller hydrothermal systems to dry due to proximity with magmatic bodies 169 . Thus, for the purpose of this classification, we will consider that a developed hydrothermal system is either present or absent.

We have chosen three parameters, each with two end-member cases, thus yielding 2 3  = 8 possible combinations. Each combination corresponds to a type of volcano that will be susceptible to different triggering mechanisms. For the purpose of brevity, we limit the analysis to the five most common types, shown in Table  1 . For each type, we provide a natural example and a list of the most efficient triggering mechanisms (Table  1 ). Importantly, volcanoes are not fixed in a given type but rather move between different categories with time, for example bimodal volcanoes can erupt two different viscosity magmas (e.g. Yellowstone, USA 184 ). Timescales for these changes span orders of magnitudes from minutes (e.g. bubble nucleation) to millennia (e.g. fractional crystallization).

Earthquakes

The characteristics of the stress perturbation also play a major role in determining whether a given mechanism will trigger activity 6 . These characteristics will result from a combination of (a) the earthquake’s attributes and (b) the volcano’s location with respect to the epicentre. Each earthquake features a unique set of characteristics (e.g. magnitude, focal mechanism, depth), and its effects can be dramatically different from one location to another 185 . This will depend mainly on distance to the epicentre but also direction and local site amplification factors 186 , 187 . Moreover, some physical mechanisms are sensitive to the frequency of incoming seismic waves 115 , 119 . Hence, our choice of parameters should reflect this complexity whilst being simple enough for our classification to be effective. As for section “Volcano types”, we have chosen three keys: (1) peak ground velocity, (2) frequency and (3) static stress change amplitude. We consider two possible end-member values for each one, yielding 2 3  = 8 different scenarios.

The first parameter is peak ground velocity (PGV), referring to the largest shaking speed effectively felt at the magma reservoir location. This value will generally depend on a number of variables such as earthquake magnitude, distance and direction to the hypocentre, or country rock structure. For example, higher magnitudes and shorter distances will generally yield stronger PGVs (and vice versa). The distribution of PGVs can be directional, with stronger PGVs in the rupture direction 147 , 185 . There may also be an increase in PGV at certain great distances from the epicentre due to SmS arrivals 186 , 188 , 189 , 190 . Similarly, seismic waves may be focused by local crustal heterogeneities or amplified by topographic irregularities, thus resulting in significantly higher local PGVs 42 , 187 , 191 , 192 , 193 , 194 . We focus on two possible cases: strong and moderate PGVs. We adopt the criterion that strong PGVs may produce a magmatic response, whereas moderate PGVs only affect hydrothermal systems 15 , 132 (and implicitly assume that there may exist very weak PGVs that do not trigger any response). This choice is motivated by field observations that hydrothermal systems are triggered by much smaller dynamic stresses than magmatic systems 6 , 15 , 51 , 59 , 60 , 195 .

The second parameter is frequency (or alternatively wave-period). Most processes are greatly enhanced when the driving frequency approaches the system’s resonance frequency. The resonance frequency of a magmatic reservoir depends on its size, geometry and the acoustic property of fluid 196 . It is generally in the range 0.001–1 Hz 115 , 119 , 196 . On the other hand, hydrothermal systems have higher resonance frequencies—typically 0.5–5 Hz 196 , 197 . Most local earthquakes exhibit frequencies related to the propagation of surface wave components in the range 1–10 Hz, but only very large earthquakes display frequencies components below 1 Hz. Frequency is particularly relevant for melt and volatiles processes. For instance, sloshing and edifice resonance have been shown to occur only at very low frequencies 115 , 119 . Regarding bubble nucleation and growth processes, experimental results on magma are unavailable, but analogy with other low viscosity fluids suggests that frequency plays a capital role 94 . Regarding permeability changes in hydrothermal systems, frequency of incoming waves is also a crucial parameter, regardless of the mechanism considered 59 , 159 , 198 . Hence, we consider two limiting cases, low and high frequencies, with the low-frequency condition being matched when frequencies lower than 1 Hz are present. These frequency choices encompass two important frequency ranges for seismicity at volcanic systems; so called long-period (LP) earthquakes and tremor (at 2–5 Hz) and very-long period (VLP) seismicity (at 0.1–0.03 Hz) and hence relate to the periods of natural excitation and resonance in the volcanic edifice.

The third parameter is static stress change amplitude. Static stress changes are highly directional, i.e. the type and magnitude of the change will strongly depend on the azimuth with respect to the epicentre. Static stress changes at and around a volcano can be numerically computed 199 , and such approaches have been successfully applied to a multitude of volcanic complexes such as Mt. Fuji 72 , Kilauea 200 , Mauna Loa 69 , Pinatubo 83 , Karymsky 70 , Cerro Negro 29 , 68 , Sierra Negra 75 , Copahue 73 , Vesuvius 67 , Mt. Etna 34 , 201 , Merapi 202 , Sinabung 203 , Mt Aso 74 and Stromboli 34 . We follow the generally accepted view that large static stress changes, both extensional and compressional, have the potential to trigger significant volcanic responses, whereas small stresses will be mostly negligible and leave the system unchanged. It is common to use 10 kPa as a limit under which static stresses can be considered negligible, since this is approximately the magnitude of ocean tidal stresses 6 . For our classification, we restrict our attention to two end-member cases, namely large (>10 kPa) and low (<10 kPa) amplitudes.

A new framework to examine seismic triggering of volcanoes

We have identified five common volcanic types as well as eight different seismic scenarios, yielding a total of 5 × 8 = 40 possible combinations. For each of these 40 cases, we examine the viable seismic-triggering mechanisms with the given conditions. The results are presented in Table  2 , which then constitutes a first-order classification of volcanoes, based on physical mechanisms with the potential for seismic-triggering.

Each column in Table  2 represents one of the five different volcano types defined in section “Volcano types”, each featuring a different set of our three volcanic parameters. Each line in Table  2 represents a different earthquake scenario, based on the three seismic parameters discussed in section “Earthquakes”. Each cell from Table  2 therefore illustrates a unique combination of an earthquake scenario with a specific volcano type, and lists the relevant mechanisms. This does not indicate that these mechanisms will necessarily happen in the case of a corresponding earthquake, but is rather an indication of which mechanisms are physically realistic with the given set of parameters. By extension, absent mechanisms are unlikely to trigger eruptions.

The first key outcome from Table  2 is that there is no empty column, meaning that all the volcano types presented may be seismically triggered. This result matches previous historical observations 8 , 10 , 16 , 33 , 56 that seismic triggering can happen for any type of volcano, in any tectonic setting. Furthermore, recent observations suggest that fluid movements dominate the response in the case of low-viscosity systems, whereas for more viscous systems, elastic processes may play a more important role 17 , 204 . This discrepancy is also captured in Table  2 : the low-viscosity columns feature many more mechanisms associated with fluid movements (e.g., sloshing, advective overpressure, shaking-induced migration) than the high-viscosity cases.

Table  2 also reinforces the role of hydrothermal systems. Many studies highlight that hydrothermal areas are particularly sensitive to seismic perturbations 6 , 42 , 48 , 52 , 53 , 128 , 156 , 170 . Hydrothermal systems sit at a strategic location and constitute a key link between magmatic reservoirs and their environments. As such, it is important to carefully examine their role in eruption triggering 4 , 138 , and in particular, as intermediate between tectonic earthquakes and volcanic eruptions.

The second key observation from Table  2 is the disparity in the numbers of mechanisms, with values ranging between zero and six. It is tempting to directly relate the number of mechanisms in a cell to the likelihood of a seismically triggered eruption to occur, but this would most likely be erroneous. Table  2 does not include any quality assessment, i.e. it does not mention how efficient and how well understood is each mechanism. Some mechanisms are supported by an extensive range of theoretical and experimental data (e.g. static triggers, permeability changes in hydrothermal systems). Others rely on analogy or idealized assumptions (e.g. advective overpressure, bubble nucleation, falling crystal roofs). Section “Triggering mechanisms” provides some information on what supporting data are available for each mechanism and more quantitative considerations can be found in previous reviews 4 , 6 , 59 . A future improvement of this work could be to define and compute an effectiveness parameter for each mechanism. Another interesting future step would be to consider whether different mechanisms may occur simultaneously, interact and possibly compound their effects 64 .

It is a delicate task to assess whether a given eruption was seismically triggered 6 , 24 , but it is even more challenging to identify the responsible mechanism(s). The three volcanic parameters presented here can be assessed for most eruptions, thus constraining the possible mechanisms. These mechanisms may then be tested for validity. For instance, static stress changes can be computed numerically 35 , 69 , 72 , 73 , occurrence of resonant oscillations can be measured, crystal and bubble textures may retain a signature of nucleation events, and hydrothermal processes can be constrained with seismic monitoring 205 and electromagnetic surveys 206 . Constraining the triggering mechanisms for a given type of volcano will be useful for future statistical studies, but may also inform and guide monitoring strategies and hazard assessment.

The importance of critical state

A significant number of cells in Table  2 are empty (six, excluding the last line). This corroborates observations that seismically triggered eruptions are a rare occurrence 7 . One of the reasons why earthquakes do not trigger more volcanic eruptions, and why some very large earthquakes trigger very little activity (e.g. Sumatra M9.2 2004 earthquake 6 ), is that the range of conditions where seismic triggering is possible forms a very narrow window that is not often met 7 , 35 . In particular, many studies have highlighted the need for a volcano to already be in a critical state in order to be seismically triggered 4 , 6 , 7 , 10 , 13 , 19 , 25 , 27 , 32 , 33 , 48 , 56 , 57 , 137 , 207 . Conceptually, a volcano may be considered in a critical state if it is close to erupting. This concept is particularly difficult to quantify, since criticality may take different forms at different volcanoes. For instance, Manga and Brodsky 6 compare the overpressure in the magma chamber to the necessary tensile stress to initiate and sustain dyking to broadly estimate the degree of criticality. Bebbington and Marzocchi 7 propose a “clock advance” mechanism, similar to what is found in the triggered-seismicity literature 208 . In this view, earthquakes merely accelerate the countdown to the next, inevitable eruption. Seismically triggered eruptions are then a consequence of a volcano being particularly advanced in its cycle towards eruption. For instance, the 1996 simultaneous eruptions of Karymsky Volcano and Akademia Nauk volcano occurred 2 days after an M w 7.1 earthquake, but also marked the end of 14 years of continuous inflation 70 . This concept also offers an explanation to why the M9.2 Sumatra 2004 earthquake did not seem to trigger any eruption, despite being located in one of the most active volcanic zones in the world 6 , 33 . It is possible that none of the nearby volcanoes were close to erupting at the time. Although rarely reported, it appears that volcanoes that are not in a critical state can still be seismically triggered into eruption. For example, La Femina et al. 29 describe the deposit of an eruption that would have seemingly not been possible to erupt without an earthquake. It is a formidable task to provide a universal definition of critical state, and something to consider for government agencies when assigning alert levels 209 as it is important for seismic triggering. At the very least, the presence of magma within reasonable distance to the surface appears to be a necessary condition, without which the cases presented in Table  2 are less relevant.

The discussion above highlights the difficulty to define what constitutes a seismically triggered eruption. An eruption is the culmination of a cascade of intertwined processes (magma generation, transport, storage, pressurization, fragmentation, etc…), and a single tectonic event cannot be held responsible for this entire chain. Earthquakes may have a less direct influence, and impact many of the different steps towards eruption (e.g. magma generation or melt segregation). For instance, seismic waves may play a key role in unlocking mushes 210 , 211 , 212 , 213 or promoting diapirs via instabilities 214 . These processes will in turn exert some control of the timing and style of eruption, but here we consider that such mechanisms do not trigger eruptions stricto sensu and thus lie beyond the scope of this study. We do nonetheless acknowledge their important role. Similarly, we mentioned the case of external triggers in section “External triggers”—sequences of events where an earthquake triggers a non-volcanic phenomenon which itself causes an eruption, and why we do not take them into account in our classification. Furthermore, for both the 1707 Fuji and 1991 Pinatubo eruptions, it was suggested that the static stress perturbation from an earthquake allowed basaltic magma to intrude into a dacitic reservoir, leading to magma mixing and eventually a Plinian eruption 72 , 83 . The static stress mechanism does fit within our classification, but it did not trigger the eruption per se. An elegant solution proposed by Marzocchi 57 is to use the term “promote” rather than “trigger” in order to emphasize the complex nature of these processes.

Changes in unrest vs. eruption

A key observation from natural events is that earthquakes trigger a change in unrest more often than a magmatic eruption 17 , 22 , 27 , 28 , 42 , 215 , 216 . Here, we adopt the general view that unrest refers to any deviation from baseline behaviour and can take various geophysical or geochemical forms 168 , 217 , 218 . In the special case of seismically triggered unrest, volcanic seismicity is, by far, the most commonly reported phenomenon 42 , 45 , 62 , 122 , 132 , 219 , 220 . Other reported processes may include increased degassing 17 , 47 , changes in fumarolic activity 45 , 48 , thermal activity 26 , 27 , 28 or gas chemistry 46 . Reports and information about unrest are not as well reported as eruption data, due to the subjective definition of “baseline behaviour” or the lesser impact unrest may cause to surrounding communities 218 . Yet, unrest episodes are generally directly identified as being related to the earthquakes (most often on the basis of spatio-temporal coincidence with the passage of seismic waves), whereas eruptions generally receive more careful statistical and physical analyses before a correlation is established 24 . Seismically triggered unrest is thus quite commonly accepted whereas seismically triggered eruptions retain some controversy.

For our purposes, a decisive question is whether the mechanisms responsible for triggered-unrest differ from the ones discussed previously. Many reports highlight that the onset of unrest seems to match seismic waves arrival, suggesting a dynamic origin 22 , 47 , 48 , 52 , 132 , 202 . For instance, triggered seismicity is likely caused by small changes in permeability in hydrothermal systems, allowing geothermal fluids to migrate and change the local stress state 90 . Therefore, unrest may be triggered without the magmatic system being in a critical state, hence explaining the more frequent occurrence of triggered-unrest compared to triggered-eruptions.

Future directions

Our framework highlights that hydrothermal systems may be more sensitive than magma to changes induced by seismic activity. This could lead to heightened unrest in the hydrothermal system and to eruption if the magmatic system is in a critical state. The link between hydrothermal systems and magmatic systems is a key area for future research, with a particular focus on the role of fracture formation, fluid migration and wave propagation through the hydrothermal and magmatic systems and in particular the magma-hydrothermal transition zone. Increasing awareness about the interplay between the hydrothermal and magmatic systems might improve volcano monitoring outcomes in the aftermath of large earthquakes.

Monitoring approaches might more specifically address changes at hydrothermal systems and magmatic systems. Ground displacement studies and volcano geodesy, seismicity and tomography, geochemistry and petrology will soon have resolutions high enough to spatially and temporally distinguish the triggered effects at hydrothermal and magmatic systems. Regarding the mechanisms with the magma, current advances in high-temperature experimental facilities now allow for tests to be run at natural conditions. We suggest that this is an important step towards refining our understanding of the processes at stake here. In combination with further and more detailed analysis of ground monitoring and satellite data, the different volcano and hydrothermal effects might become distinguished following different types of earthquakes. Finally, as our records of earthquakes and heightened volcano unrest expands, it remains necessary to regularly update statistical and modelling analyses.

Data availability

The authors declare that the data supporting the findings of this study are available within the paper.

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Acknowledgements

We thank Sriparna Saha for her help in improving the quality of the figures. G.S., B.K., and T.W. were supported by a Marsden grant. A.J. was funded by the Ministry of Business Innovation and Employment (MBIE) Strategic Science Investment Fund (SSIF).

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G.S. drafted the initial MS and figures, with the participation of B.K. T.W. provided background on natural observations and statistical significance. M.I. provided background on physical mechanisms. A.J. provided seismological context. All authors contributed to the design of the ideas presented and the final version of the paper.

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Seropian, G., Kennedy, B.M., Walter, T.R. et al. A review framework of how earthquakes trigger volcanic eruptions. Nat Commun 12 , 1004 (2021). https://doi.org/10.1038/s41467-021-21166-8

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The surface of the Earth is made up of tectonic plates that lie beneath both the land and oceans of our planet. The movements of these plates can build mountains or cause volcanoes to erupt. The clash of these plates can also cause violent earthquakes, where Earth’s surface shakes. Earthquakes are more common in some parts of the world than others, because some places, like California, sit on top of the meeting point, or fault, of two plates. When those plates scrape against each other and cause an earthquake, the results can be deadly and devastating.

Learn more about earthquakes with this curated collection of classroom resources.

Geology, Geography, Physical Geography

143 Earthquake Essay Topics & Examples

Need a catchy title for an earthquake essay? Earthquakes can take place almost everywhere. That is why this problem is so exciting to focus on.

🏆 Best Earthquake Topic Ideas & Essay Examples

🎓 good essay topics on earthquake, 📌 catchy titles for earthquake essay, 👍 research titles about earthquake, ❓ essay questions about earthquake.

In your earthquake essay, you might want to compare and contrast various types of this natural disaster. Another option is to talk about your personal experience or discuss the causes and effects of earthquakes. In a more serious assignment like a thesis or a term paper, you can concentrate on earthquake engineering or disaster management issues. In this article, we’ve gathered best research titles about earthquake and added top earthquake essay examples for more inspiration!

• Crisis Management: Nissan Company and the 2011 Earthquake Expand on the points made in the case to identify the potential costs and benefits of these actions. The sharing of information was quite beneficial to Nissan in its response to the disaster.
• Natural Disasters: Tornadoes, Earthquakes, and Hurricanes Hence the loss may depend on the population of the area affected and also the capacity of the population to support or resist the disaster.
• Earthquake in South Africa: Reconstruction Process Therefore, it is vital for the government of South Africa to address the issues caused by the earthquake and reconstruct the region, focusing on several public interventions to stimulate the region’s growth in the shortest […]
• Mitigation of Earthquake Hazards The geologists should also inform the architects on the areas where earthquakes are likely to occur and how strong they will be able.
• Public Awareness of Earthquake This will mean that the basement that is involved in thickening and shortening is mechanically required to produce the shape of zagros belt.
• Natural Disasters: Earthquakes, Floods and Volcanic Eruption This is due to the relationship between an eruption and the geology of the area. It was observed that the mountain swelled and increased in size due to the upward force of magma.
• Earthquakes and Their Devastating Consequences The break in the ground surface is the most common cause of horrific consequences, and people often cannot get out of the epicenter of the incident.
• Natural Disasters: Earthquakes, Volcanoes, and Tsunamis In addition, the paper will outline some of the similarities and differences between tsunamis and floods. Similarities between tsunamis and floods: Both tsunamis and floods are natural disasters that cause destruction of properties and human […]
• Earthquakes Impact on Human Resource in Organizations The researcher seeks to determine the magnitude of this effect and its general effect on the society in general and the firms affected in specific.
• Disaster Preparedness and Nursing: A Scenario of an Earthquake In a scenario of an earthquake, nursing staff must be aware of the stages of disaster management and disaster preparedness in particular.
• Recent Earthquakes and Safety Measures in California and Nevada The earthquake that is the largest by magnitude is in California. It is possible to minimize the damage by an earthquake.
• Theory of Disaster: Earthquakes and Floods as Examples of Disasters The second category is that of those people who put their focus on the effects of the social vulnerability or the disasters to the society or to the people who are likely to be the […]
• Earthquakes in Chile and Haiti Moreover, the quake in Haiti raptured at the epicenter of the city with a high population density compared to Chile. Therefore despite a lower magnitude earthquake than Chile, Haiti suffered more damage due to the […]
• Earthquake Prevention From Healthcare Perspective In terms of primary prevention of such a disaster, it is necessary to establish a public body or organization responsible for the creation of an extensive network of food, water, and first-aid kits to last […]
• Analysis of Damage to Apartment Buildings in the 1989 Loma Prieta Earthquake In turn, it is a prerequisite for the cataclysms in nature, such as earthquakes and the effect of liquefaction which was particular to the Marina district in the disaster of 1989.
• The 1979 Tangshan Earthquake The Tangshan Earthquake happened in 1976 is considered to be one of the large-scale earthquakes of the past century. The 1975 Haicheng Earthquake was the first marker of gradual and continuous intensification of tectonic activity […]
• School Preparedness Plan for Tornado, Earthquakes, Fire Emergency In case of an earthquake emergency, the school should be prepared to keep the students safe. In case of a tornado emergency the school should be prepared to keep the students safe.
• Earthquake in Haiti 2010: Nursing Interventions During natural disasters, such as the catastrophic earthquake in Haiti in 2010, nursing interventions aim to reduce the level of injury and provide the conditions for the fast recovery of its victims.
• Earthquake Risk Reduction: Challenges and Strategies The victims of the earthquake in Haiti were hundreds of people, while the number of wounded and homeless was in the thousands. As for the latter, the worst scenario of the earthquake is created and […]
• Role of the Nurses in the Site of the Haiti Earthquake The primary aim of the tertiary intervention conducted by the health practitioners was to reduce the effect of the diseases and injuries that occurred because of the Haiti earthquake.
• Volcanoes: Volcanic Chains and Earthquakes The “Ring of Fire” is marked by the volcanic chains of Japan, Kamchatka, South Alaska and the Aleutian Islands, the Cascade Range of the United States and Canada, Central America, the Andes, New Zealand, Tonga, […]
• Earthquakes: Causes and Consequences The first of these are body waves, which travel directly through rock and cause the vertical and horizontal displacement of the surface.
• The Impacts of Japan’s Earthquake, Tsunami on the World Economy The future prospects in regard to the tsunami and the world economy will be presented and application of the lessons learnt during the catastrophe in future” tsunami occurrence” management.
• Natural vs. Moral Evil: Earthquakes vs. Murder This problem demonstrates that such justifications for the problem of evil, such as the fact that suffering exists to improve the moral qualities of a person and thus serve the greater good, are unconvincing.
• Review of Earthquake Emergency Response The second resource is the supply of food and water that can help survivors wait for the rescue team for three days.
• California Earthquakes of the 20th Century Ultimately, the current essay examines the most devastating earthquakes in California in the 20th century and proposes a hypothesis of when the next large earthquake might strike.
• Human Activity and Growing Number of Earthquakes The pieces that support the opposing view claim that the data about their number may be distorted due to the lack of difference in the development mechanism of natural and artificial earthquakes.
• Researching the Earthquake Due to human activity, artificial earthquakes occur, and their number increases every year following the strengthening of destructive human impact on the planet.
• Earthquake Disasters: Medical Response and Healthcare Challenges Therefore, an earthquake disaster infers abrupt and immense shaking of the ground for a duration and magnitude that can infringe the day-to-day activities. The last role of healthcare personnel in triage and intervention is to […]
• Haiti Earthquake of 2010 Overview The purpose of this paper is to review the location and physical cause of the event, its human impact from it, and some of the interesting facts related to the disaster.
• Wenchuan Earthquake: Impact on China’s Economy The earthquake made a moderate impact on the country’s economy, yet affected several industries located in the devastated areas.
• The Japan Earthquake and Tsunami of 2011 Documentary The documentary reflects the events leading to the natural disasters and their aftermath, including an investigation into the reasons for the failure of the precautionary measures in place during the 2011 earthquake in Japan.
• A Geological Disaster: Nisqually Earthquake in Washington State Geology refers to the study of the processes that lead to the formation of rocks and the processes that contribute to the shape of the earth.
• The Huaxian Earthquake: China’s Deadliest Disaster The main reason for the terrible earthquakes consequences was in the absence of a plan for the emergency case. After visiting China later in 1556, he wrote that the given disaster was likely to be […]
• The Sumatra Earthquake of 26 December 2004: Indonesia Tsunami As such, the earthquake resulted in the development of a large tsunami off the Sumatran Coast that led to destruction of large cities in Indonesia.
• Understanding Plate Tectonics and Earthquakes: Movements, Causes, and Measurement Therefore, the distance of the fracture will determine the intensity of the vibrations caused by the earthquake and the duration of the effect, that is, shaking the ground.
• Review of Public Meeting Regarded Earthquakes This focused meeting held in Port Au-Prince was to formulate the best strategies to help the people of Haiti anticipate, adapt and also recover from the impacts of earthquakes.
• Rebuilding Haiti: Post-Earthquake Recovery No doubt the tremors have taken a massive toll on the lives and resources of Haiti, but it was not only the tremors that caused the damage to such a massive extent.
• Earthquake Impacts: A Case Study of the 2010 Haiti Earthquake The short-term effects of the earthquake include food shortage, lack of clean water; breakdown of communication, lack of sufficient medical care, closure of ports and main roads, increased mortally, injuries, fires, the spread of communicable […]
• Sichuan Earthquake and Recovering as Community Problem We plan to give these pamphlets to businessmen in China and we have also uploaded these pamphlets on the internet for all the people around the world to see and to support this great cause.
• Natural Hazard: Tsunami Caused by Earthquakes Other areas that are prone to the tsunamis include Midwestern and Eastern United States of America and parts of Eastern of Canada, Indian Ocean and East Africa.
• Emergency Response to Haiti Earthquake The response to the earthquake and calamities that followed was a clear demonstration that the country was ill-prepared to deal with such a disaster.
• Haiti and Nepal Earthquakes and Health Concerns As applied to the environment in these countries, roads were disrupted and, in some parts of the area, people could not be provided with the necessary amounts of food and drinking water.
• Hypothetical New York Earthquake Case Therefore, the following faults would be included in the report as potential causes of the earthquake: the 125th Street fault is the largest of all.
• 1906 San Francisco Earthquake: Eyewitness Story The moon crept in and out of the room, like a late evening silhouette, but its lazy rays did little to signal us what we would expect for the rest of the day.
• Scientists’ Guilt in L’Aquila Earthquake Deaths Additionally, there is another issue related to the development of scientific knowledge, which takes time as it is subjected to a lot of criticism before it is adopted.
• Dangerous and Natural Energy: Earthquakes The distribution of earthquakes in the world varies according to the region. Click on one of the earthquakes on the map and make a note of its magnitude and region.
• Earthquake Emergency Management and Health Services Fundamental principles of healthcare incident management involve the protection of people’s lives, the stabilization of the disaster spot, and the preservation of property.
• Fracking: Increased Seismic Activities in Kansas According to the report of the State Corporation Commission of the State of Kansas, the work of local drilling companies has considerably increased the number of seismic activities in the state.
• Earthquake as a Unique Type of Natural Disaster Earthquakes are believed to be one of the most dangerous natural disasters, and they can have a lot of negative effects on both the community and the environment.
• US Charities in Haiti After the 2010 Earthquake This paper aims to explore the overall implications of the earthquake and the response to it, as well as to provide an examination of the actions of three U.S.-based NGOs, which contributed to the restoration […]
• Christchurch Earthquakes’ Impact on New Zealand Businesses Similarly, the occurrence of the incident led to the loss of lives that had the potential of promoting most businesses into great heights.
• Understanding Earthquake Statistics: Frequency, Magnitude, and Data Sources Tectonic earthquakes are prompted as a consequent of movement of the earth’s crust because of the strain. The USGS National Earthquake Information Center reports an increase in the number of detection and location of earthquakes […]
• Natural Disasters: Tsunami, Hurricanes and Earthquake The response time upon the prediction of a tsunami is minimal owing to the rapid fall and rise of the sea level.
• Geology Issues: Earthquakes The direction of the plates’ movements and the sizes of the faults are different as well as the sizes of tectonic plates.
• 2008 and 2013 Sichuan Earthquakes in China This was the worst and the most devastating earthquake since “the Tangshan earthquake of 1976 in China”. In addition, impacts differ based on the number of fatalities and damages to property.
• Haiti Earthquake Devastation of 2010 In addition, most of the personnel who were part and parcel of the recovery teams were lost in the disaster making it difficult to reach out for the victims.
• Mitigation for Earthquake and Eruption Since the energy is mainly derived from the sustained stress and deformation of the underlying rocks, the precursor signals of earthquakes especially in seismic zones are majorly based on the careful study of the earth’s […]
• Earthquakes in New Madrid and Fulton City, Missouri The accumulation of this stress is a clear indication of the slow but constant movement of the earth’s outermost rocky layers.
• Tōhoku Earthquake of 2011 The rate at which the pacific plate undergoes displacement is at eight to nine centimeter per annum, hence the plate subduction of the plate led to a discharge of large amounts of energy leading to […]
• Earthquakes as a Cause of the Post Traumatic Stress Disorder Although earthquake is a major cause of the post traumatic stress disorder, there are other factors that determine the development of the same.
• Plate Tectonics, Volcanism, Earthquakes and Rings of Fire Plate tectonics has led to the separation of the sea floor over the years and the earth is composed of seven tectonic plates according to the available geological information.
• The 2011 Great East Japan Earthquake The earthquake was accompanied by a great tsunami given the high magnitude of the earthquake that reached 9. The third disaster was the meltdown of a number of nuclear plants following the tsunami.
• The Parkfield Earthquake Prediction Experiment The seismic activity and the relatively regular sequence of the earthquakes in the area of San Paul Fault generated the interest of the geologists in exploring the processes in the rupture.
• Earthquakes: Definition, Prevalence of Occurrence, Damage, and Possibility of Prediction An earthquake is a dangerous tremor that is caused by sudden release of energy in the crust of the earth leading to seismic waves that cause movements of the ground thus causing deaths and damages.
• Losing the Ground: Where Do Most Earthquakes Take Place? Since, according to the above-mentioned information, natural earthquakes are most common in the places where the edges of tectonic plates meet, it is reasonable to suggest that earthquakes are most common in the countries that […]
• Geology Issue – Nature of Earthquakes Such an earthquake is caused by a combination of tectonic plate movement and movement of magma in the earth’s crust. Continental drift is the motion of the Earth’s tectonic plates relative to each other.
• The Great San Francisco Earthquake The length however depends on the size of the wave since the larger the wave the larger the area affected and consequently the longer the period of time taken.
• The Impact of the California Earthquake on Real Estate Firms’ Stock Value
• Technology Is The Best Way To Reduce The Impact of An Earthquake
• Study on Earthquake-Prone Buildings Policy in New Zealand
• The Devastating Effects of the Tohuku Earthquake of 2011 in Japan
• The Disasters in Japan in 2011: The Tohoku Earthquake and Tsunami
• Why Was the Haiti Earthquake So Deadly
• Taking a Closer Look at Haiti After the Earthquake
• The Aftermath of The Earthquake of Nepal
• The Effects of the Fourth-Largest Earthquake in Japan in Problems Persist at Fukushima, an Article by Laurie Garret
• The Greatest Loss of The United Francisco Earthquake of 1906
• The Impact of Hurricanes, Earthquakes, and Volcanoes on Named Caribbean Territories
• The Destruction Caused by the 1906 San Francisco Earthquake
• Foreshocks and Aftershocks in Earthquake
• The Great San Francisco Earthquake and Firestorm
• Scientific and Philosophic Explanation of The 1755 Lisbon Earthquake
• The Haiti Earthquake: Engineering and Human Perspectives
• Voltaire and Rousseau: A Byproduct of The Lisbon Earthquake
• The Great East Japan Earthquake’s Impact on the Japanese
• Estimating the Direct Economic Damage of the Earthquake in Haiti
• What Should People Do Before, During, and After an Earthquake
• What to Do Before, During, and After an Earthquake
• Valuing the Risk of Imperfect Information: Christchurch Earthquake
• The Impact of the Earthquake on the Output Gap and Prices
• The Devastating Earthquake of The United States
• The Earthquake of The Sumatra Earthquake
• The Crisis of the Fukushima Nuclear Plant After an Earthquake
• The Impact of The San Francisco Earthquake of 1906
• The History and Effects of the Indian Ocean Earthquake and Tsunami in 2004
• The Effects of an Earthquake Ledcs
• The Cascadia Earthquake: A Disaster That Could Happen
• The Economy in the Aftermath of the Earthquake
• The Impact of Earthquake Risk on Housing Market Before and After the Great East Japan Earthquake
• Who Benefit From Cash and Food-for-Work Programs in Post-Earthquake Haiti
• Macro Effects of Massive Earthquake Upon Economic in Japan from 2011 to 2013
• How the 1906 San Francisco Earthquake Shaped Economic Activity in the American West
• The Cause of Earthquakes and the Great San Francisco Earthquake of 1906
• The Effect of the Earthquake in Haiti: Global Issues
• Understanding How Gigantic Earthquake and Resultant Tsunami Are Being Formed
• Why God and The Earthquake of Haiti Happened
• The Effects of the Great East Japan Earthquake on Investors’ Risk and Time Preferences
• The Great East Japan Earthquake and its Short-run Effects on Household Purchasing Behavior
• Internal Displacement and Recovery From a Missouri Earthquake
• Understanding the Causes and Effects of an Earthquake
• Supply Chain Disruptions: Evidence From the Great East Japan Earthquake
• The Earthquake That Shook The World In Pakistan
• What Motivates Volunteer Work in an Earthquake?
• Who Benefits From Cash and Food-For-Work Programs in Post-earthquake Haiti?
• Why Did Haiti Suffer More Than Kobe as a Result of an Earthquake?
• Why Did the Earthquake in Haiti Happen?
• Why Does the Earthquake Happen in Chile?
• Why Was the Haiti Earthquake So Deadly?
• Was the Japan Earthquake Manmade?
• How Did the 1964 Alaska Earthquake Enhance Our Understanding?
• How Does the Theory of Plate Tectonics Help to Explain the World Distribution of Earthquakes and Volcanic Zones?
• How Leaders Controlled Events in the 1906 San Francisco Earthquake?
• How Shaky Was the Regional Economy After the 1995 Kobe Earthquake?
• How Would Society React to Modern Earthquakes, if They Only Believed in Myths?
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Geography Notes

Essay on earthquakes: top 5 essays on earthquakes | geography.

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Here is a compilation of essays on ‘Earthquakes’ for class 6, 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Earthquakes’ especially written for school and college students.

Essay on Earthquakes

Essay Contents:

• Essay on the World Distribution of Earthquakes

Essay # 1. Introduction to Earthquake:

An earthquake is a major demonstration of the power of the tectonic forces caused by endogenetic thermal conditions of the interior of the earth. ‘An earthquake is a motion of the ground surface, ranging from a faint tremor to a wild motion capable of shaking buildings apart and causing gaping fissures to open in the ground.

The earthquake is a form of energy of wave motion transmitted through the surface layer of the earth in widening circles from a point of sudden energy release, the focus’. ‘An earthquake is a vibration or oscillation of the surface of the earth caused by a transient distur­bance of the elastic or gravitational equilibrium of the rocks at or beneath the earth the surface.’

The magnitude or intensity of energy released by an earthquake is measured by the Richter Scale devised by Charles F. Richter in 1935. The number indicating magnitude or intensity (M) on Richter scale ranges between 0 and 9 but in fact the scale has no upper limit of number because it is a logarithmic scale.

It is estimated that the total annual energy released by all earthquakes is about 10 25 ergs, most of this is from a small number of earthquakes of magnitude over 7. The 1934 Bihar earthquake measuring 8.4 and Good Friday Earthquake of March 27, 1964 in Alaska (USA) meas­uring 8.4 to 8.6 on Richter scale are among the greatest earthquakes of the world ever recorded.

The place of the origin of an earthquake is called focus which is always hidden inside the earth but its depth varies from place to place. The deepest earth­quake may have its focus at a depth of even 700 km below the ground surface but some of the major Himalayan earthquakes, such as the Bihar-Nepal earth­quake of August 21, 1988, have their focus around 20- 30 km deep.

The place on the ground surface, which is perpendicular to the buried ‘focus’ or ‘hypocentre’, recording the seismic waves for the first time is called epicentre. The waves generated by an earthquake are called ‘seismic waves’ which are recorded by an in­strument called seismograph or seismometer at the epicentre. The science, that deals with the seismic waves, is called seismology.

Essay # 2. Causes of Earthquakes :

Earthquakes are caused mainly due to disequi­librium in any part of the crust of the earth. A number of causes have been assigned to cause disequilibrium or isostatic imbalance in the earth’s crust such as volcanic eruptions, faulting and folding, up-warping and down-warping, gaseous expansion and contraction inside the earth, hydrostatic pressure of man-made water bodies like reservoirs and lakes, and plate move­ments.

If we look at the world distribution of earth­quakes (fig. 10.2) it appears that the earthquake belts are closely associated with the weaker zones and isostatically disturbed areas of the globe. It was gener­ally believed that isostatically balanced and old and stable rigid masses were free from seismic events but the devastating earthquake of Koyna on 11 December, 1967, in Satara district of Maharashtra, Latur-Kilari earthquake of Sept. 30, 1993 of Maharashtra, dis­ proved this old connotation and made us believe that no part of the earth is immune from seismic events. A host of possible causes have been suggested to cause disequilibrium in the earth’s crust which trigger earth tremors of various sorts.

i. Vulcanicity:

Volcanic activity is considered to be one of the major causes of earthquakes. In fact, vulcanicity and seismic events are so intimately related to each other that they become cause and effect for each other. In other words, each volcanic eruption is followed by earthquakes and many of the severe earthquakes cause volcanic eruptions.

In fact, earth tremors are major precursor events of possible volcanic eruption in im­mediate future in any region. The explosive violent gases during the process of vulcanicity try to escape upward and hence they push the crustal surface from below with great force and thus is caused severe earth tremor of high magnitude.

Whenever these gases be­come successful in breaking the weak crustal surface they appear on the earth’s surface with violent explo­sion and great force causing devastating volcanic erup­tion which causes sudden disequilibrium in the crustal surface to invite severe earth tremors. It may be pointed out that the magnitude of such earthquakes depends upon the intensity of volcanic eruptions.

The violent eruption of Krakatoa volcano (between Java and Sumatra) caused such a severe earthquake the impact of which was experienced as far away as Cape Horn (some 12,800 km away). The devastating earth­quake generated 30 to 40 m high tsunamis waves which killed 36,000 people in the coastal areas of Java and Sumatra.

ii. Faulting and Elastic Rebound Theory :

The horizontal and vertical movements caused by endogenetic forces result in the formation of faults and folds which in turn cause isostatic disequilibrium in the crustal rocks which ultimately causes earth­quakes of varying magnitudes depending on the nature and magnitude of dislocation of rock blocks caused by faulting and folding. In fact, sudden dislocation of rock blocks caused by both tensile and compressive forces triggers immediate earth tremors due to sudden maladjustment of rock blocks.

The 1950-earthquake of Assam was believed to have been caused due to dis­equilibrium in crustal rocks introduced by crustal frac­ture. The 1934-earthquake of Bihar was also consid­ered to have been triggered by faulting activity under­neath. Underground active fault zone was suggested as one of the possible causes of Koyna earthquake (Maharashtra) of December 11, 1967.

The occurrence of severe devastating earth­quake of San Francisco (USA) in 1906 led H.F. Reid, one of the official investigators of the San Fransisco earthquake disaster, to advance his famous and much appreciated elastic rebound theory to explain the mode and causes of earthquakes mainly caused by fractures and faults in the earth’s crust and upper mantle.

Ac­cording to Reid the underground rocks are elastic like rubber and expand when stretched and pulled. The stretching and pulling of crustal rocks due to tensile forces is slow process. The rocks continue to be stretched so long as the tensile forces do not exceed the elasticity of the rocks but as the tensile forces exceed the rocks elasticity, they are broken and the broken rock blocks try immediately to occupy their previous positions so that they may adjust themselves. All these processes occur so rapidly that the equilibrium of the concerned crustal surface is suddenly disturbed and hence earth tremors are caused.

Reid’s elastic rebound theory very well ex­plains the occurrences of seismic events in Californian valley which is very much frequented by faulting activity. The famous earthquake of 1872 of California was caused due to creation of a massive fault in the Oven Valley. Similarly, the Californian earthquake of April 18, 1906, was caused due to the formation of 640 km long San Andreas Fault. The 1923 earthquake of Sagami Bay of Japan was also believed to have been triggered by big fault.

N. Krishna Brahman and Janardhan G. Niyogi, the two scientists of the National Geophysical Re­search Institute, have opined that the seismic events near Bhatsa Dam and Koyna Dam are very much active due to active faulting beneath the Deccan Traps. They have claimed to have identified two active rift faults in Maharashtra beneath the Deccan Traps viz. Kurduvadi rift and Koyna rift.

According to them Koyna rift begins from Kaladgi in Karnataka and runs for a distance of 540 km through Koyna and terminates 40 km west of Nasik. The 390 km long Kurduvadi rift begins from 40 km south-west of Solapur and after running through Kurduvadi it merges with the Koyna rift to the north of Pune. According to them Bhatsa Dam is located at the junction of Tawi and Koyna faults.

They are of the opinion that gradual increase in the seismic events in Bhatsa Dam area since 1983 is because of active faulting beneath the basaltic crust. The 1950 Assam earthquake, 1934 Bihar earthquake and 2001 Bhuj earthquake (Gujarat) of India were caused mainly by faulting.

iii. Hydrostatic Pressure and Anthropogenic Causes :

Though the earthquakes are natural phenomena and are caused by the endogenetic forces coming from within the earth but certain human activities such as pumping of groundwater and oil, deep underground mining, blasting of rocks by dynamites for construc­tional purposes (e.g., for the construction of dams and reservoirs, roads etc.), nuclear explosion, storage of huge volume of water in big reservoirs etc. also cause earth tremors of serious consequences.

The introduc­tion of additional artificial superincumbent load through the construction of large dams and impounding of enormous volume of water in big reservoirs behind the dams cause disequilibrium of already isostatically ad­justed rocks below the reservoirs or further augment the already fragile structures due to faults and fractures underneath.

Many major seismic events have been cor­related with dams and reservoirs all over the world such as earthquake of 1931 in Greece due to Marathon Dam constructed in 1929; initiation of earth tremors since 1936 around Hoover Dam (USA) due to creation of Mead Lake in 1935; Koyna earthquake of 1967 (in Satara district of Maharashtra) due to Koyna reservoir constructed in 1962; other examples of earthquakes caused by dams and reservoirs are of Monteynard and Grandvale in France, Mangla in Pakistan, Kariba in Zambia, Manic in Canada, Hendrick Verwoerd in South Africa, Nourek in earst-while USSR, Kurobe in Japan etc.

It may be pointed out that the intensity of earthquake has been positively correlated with the levels of water in the reservoirs. The earthquakes caused by hydrostatic pressure of reservoirs are called ‘reservoir-induced earthquakes’.

iv. Plate Tectonic Theory :

Recently, plate tectonic theory has been ac­cepted as the most plausible explanation of the causes of earthquakes. As per theory of the plate tectonics the crust or the earth is composed of solid and moving plates having either continental crust or oceanic crust or even both continental-oceanic crust.

The earth’s crust consists of 6 major plates (Eurasian plate, Ameri­can plate, African plate, Indian plate, Pacific plate and Antarctic plate) and 20 minor plates. These plates are constantly moving in relation to each Other due to thermal convective currents originating deep within the earth.

Thus, all the tectonic events take place along the boundaries of these moving plates. From the stand point of movement and tectonic events and creation and destruction of geomaterials the plate boundaries are divided into:

(i) Constructive plate boundaries,

(ii) Destructive plate boundaries, and

(iii) Conservative plate boundaries.

Constructive plate boundaries repre­sent the trailing ends of divergent plates which move in opposite directions from the mid-oceanic ridges, de­structive plate boundaries are those where two conver­gent plates collide against each other and the heavier plate boundary is sub-ducted below the relatively lighter plate boundary and conservative plate boundaries are those where two plates slip past each other without any collision.

Major tectonic events associated with these plate boundaries are ruptures and faults along the constructive plate boundaries, faulting and folding along the destructive plate boundaries and transform faults along the conservative plate boundaries. All sorts of disequilibrium are caused due to different types of plate motions and consequently earthquakes of varying magnitudes are caused.

Normally, moderate earthquakes are caused along the constructive plate boundaries because the rate of rupture of the crust and consequent movement of plates away from the mid-oceanic ridges is rather slow and the rate of upwelling of lavas due to fissure flow is also slow. Consequently, shallow focus earthquakes are caused along the constructive plate boundaries or say along the mid-oceanic ridges.

The depth of ‘focus’ of earthquakes associated with the constructive plate boundaries ranges between 25 km to 35 km but a few earthquakes have also been found to have occurred at the depth of 60 km. It is, thus, obvious that the earth­quakes occurring along the mid-Atlantic Ridge, mid- Indian Oceanic Ridge and East Pacific Rise are caused because of movement of plates in opposite directions (divergence) and consequent formation of faults and ruptures and upwelling of magma or fissure flow of basaltic lavas (fig. 10.1).

Earthquakes of high magni­tude and deep focus are caused along the convergent or destructive plate boundaries because of collision of two convergent plates and consequent subduction of one plate boundary along the Benioff zone. Here mountain building, faulting and violent volcanic erup­tions (central explosive type of eruptions) cause severe and disastrous earthquakes having the focus at the depth up to 700 km.

This process, convergence of plates and related plate collision, explains the maxi­mum occurrence of earthquakes of varying magnitudes along the Fire Ring of the Pacific or the Circum-Pacific Belt (along the western and eastern margins of the Pacific Ocean or say along the western coastal margins of North and South Americas and thus the Rockies to Andes Mountain Belt and along the eastern coastal margins of Asia and island arcs and festoons parallel to the Asiatic coast).

The earthquakes of the Mid-Conti- nental Belt along the Alpine-Himalayan chains are caused due to collision of Eurasian plates and African and Indian plates. The earthquakes of the western marginal areas of North and South Americas are caused because of subduction of Pacific plate beneath the American plate and the resultant tectonic forces whereas the earthquakes of the eastern margins of Asia are originated because of the subduction of Pacific plate under Asiatic plate.

Similarly, the subduction of Afri­can plate below European plate and the subduction of Indian plate under Asiastic plate cause earthquakes of the mid-continental belt. The severe earthquake of Bhuj of Jan. 26, 2001 (Gujarat, India) was caused due to reactivated subsurface faults due to subduction of Indian plate below Asiatic plate.

Creation of transform faults along the conserva­tive plate boundaries explains the occurrence of severe earthquakes of California (USA). Here one part of California moves north-eastward while the other part moves south-westward along the fault plane and thus is formed transform fault which causes earthquakes.

Essay # 3. Classification of Earthquakes :

It has become apparent after the discussion of the causes of seismic events that there is wide range of variation in the nature and magnitude of earthquakes. Each earthquake differs from the other and thus it becomes difficult to classify all the earthquakes into certain categories.

Inspite of these limitations earth­quakes are classified on the basis of common charac­teristics as given below.

i. Classification on the basis of Causative Factors :

(A) Natural earthquakes are those which are caused by natural processes i.e., due to endogenetic forces.

These are further divided into four subcategories:

(i) Volcanic earthquakes are caused due to vol­canic eruptions of explosive and fissure types. Gener­ally, volcanic earthquakes are confined to volcanic areas. The intensity and magnitude of such earth­quakes depend on the intensity and magnitude of volcanic eruptions. Examples, severe earthquakes caused by violent explosions of Krakatao volcano in 1883 and Etna volcano in 1968.

(ii) Tectonic earthquakes are caused due to dis­location of rock blocks during faulting activity. Such earthquakes are very severe and disastrous. Examples, 1872 earthquake and 1906 earthquake of California (USA), 1923 earthquake of Sagami Bay (Japan), 2001 earthquake of Gujarat etc.

(iii) Isostatic earthquakes are triggered due to sudden disturbance in the isostatic balance at regional scale due to imbalance in the geological processes. Generally, the earthquakes of active zones of mountain building are included in this cat­egory.

(iv) Plutonic earthquakes are infact deep-focus earthquakes which occur at greater depths. The centres (foci) of these earthquakes are generally located within the depths ranging from 240 km to 670 km.

(B) Artificial or man-induced earthquakes or anthropogenic earthquakes are caused by human ac­tivities such as pumping of water and mineral oil from underground aquifers and oil reserves respectively, deep underground mining, blasting of rocks by dyna­mites for constructional purposes (e.g., for the con­struction of dams and reservoirs, roads etc.), nuclear explosion, storage of huge volume of water in big reservoirs etc.

Examples, 1931 earthquake of Greece due to Marathon Dam, 1936 earthquake of Hoover Dam (USA) due to Lake Mead, Koyna earthquake (Maharashtra, India) of 1967 due to Koyna reservoir etc.

ii. Classification on the basis of Focus :

Guttenberg has divided the world seismic cen­tres on the basis of the depths of their foci into 3 types viz.:

(i) Moderate earthquakes—foci are located at the depths from the ground surface (0 km) to 50 km,

(ii) Intermediate earthquakes-seismic foci at the depths between 50 km and 250 km and

(iii) Deep focus earthquakes-seismic foci at the depths between 250 km and 700 km. Moderate and intermediate earthquakes are also called as shallow focus and intermediate focus earthquakes respectively.

iii. Classification on the basis of Human Casualties:

Earthquakes are grouped into 3 categories on the basis of their hazardous impacts in terms of human casualties:

(i) Moderately hazardous earthquakes- When human deaths caused by severe seismic tremors are below 50,000 mark. Examples, Kamakura earth­quake of Japan of 1293 A.D. (22,000 deaths), Tabas earthquake of Iran of 1978 A.D. (25,000 deaths), Armenian earthquake of erstwhile USSR of 1988 (26,000 deaths), Lisbon earthquake of Portugal in 1531 A.D. (30,000 deaths), Chile earthquake of 1939 A.D. (40,000 deaths), Quito earthquake of Ecudador in 1797 A.D. (41,000 deaths), Calabria earthquakes of Italy in 1783 A.D. (50,000 deaths), North Iranian earthquake of 1990 A.D. (50,000 deaths) etc.

(ii) Highly hazardous earthquakes causing human deaths ranging between 51,000 and 1,00,000 occurred in 1268 (in Silicia, Asia Minor, death toll, 60,000), in 1667 (in Shemaka, Caucasia, death toll 60,000), in 1693 (Catania, Italy, 93,000 deaths), in 1693 (Naples, Italy, 93,000 deaths), in 1932 (Kansu, China, human deaths, 70,000), in 1935 (Quetta, Baluchistan, death toll, 60,000), in 1970 (Chimbote, Peru, 67,000 deaths), in 2001 (Bhuj, Gujarat, 50,000-1,00,000 death) etc.

(iii) Most hazardous earthquakes causing human casualitis above 1,00,000 mark occurred in the year 1290 (in Chihli, China, 1,00,000 deaths), in 1556 (in Shen-Shu, China, 8,30,000 deaths), in 1737 (Kolkata, India, 3,00,000 deaths), in 1908 (in Messina, Italy, 1,60,000 deaths), in 1920 (in Kansu, China 1,80,000 deaths), in 1923 (in Tokyo, Japan, 1,63,000 deaths), in 1967 (in Tang-Shan, China 7,50,000) deaths etc.

Essay # 4. Hazardous Effects of Earthquakes:

It may be pointed out that the intensity of earth­quakes and their hazardous impacts are determined not on the basis of the magnitude of seismic intensity as determined by Richter scale but are decided on the basis of quantum of damages done by a specific earth­quake to human lives and property.

An earthquake becomes hazard and desaster only when it strikes the populated area. The direct and indirect disastrous ef­fects of earthquakes include deformation of ground surfaces, damage and destruction of human structures such as buildings, rails, roads, bridges, dams, factories, destruction of towns and cities, loss of human and animal lives and property, violent devastating fires, landslides, floods, disturbances in groundwater condi­tions etc.

i. Slope Instability and Failures and Landslides:

The shocks produced by earthquakes particularly in those hilly and mountainous areas which are composed of weaker lithologies and are tectonically sensitive and weak cause slope instability and slope failure and ultimately cause landslides and debris falls which damage settlements and transport systems on the lower slope segments.

The shocks generated by Peruvian earthquake of May, 1970 triggered off the collapse of ice caps seated on the peak of high mountain called Huascaran of 6654 m height near the town of Yungay in Peru.

The huge masses of falling ice dislodged thousands of tonnes of rock mass from the said moun­tain and thus was generated a gigantic debris flow down the slope of Huascaran mountain travelling at the speed of 320 km per hour. The enormous mass of debris flow covered a distance of 15 km within few minutes and buried many buildings and human struc­tures of Yungay town and killed about 25,000 people.

ii. Damage to Human Structures:

Earthquakes inflict great damage to human structures such as build­ings, roads, rails, factories, dams, bridges, and thus cause heavy loss of human property. It may be pointed out that in the ground surface composed of unconsolidated geomaterials, such as alluvium, colluvium, artificially infilled and levelled depres­sions, swamp deposits reclaimed through the dumping of coarse sands and city garbages the vibrations of earthquakes last longer and the amplitudes of seismic waves are greater than in the structures of consolidated materials, and bedrocks. Thus, the earthquakes cause more damages in the areas of unconsolidated ground than their counterparts in the regions of solid structures and bedrocks.

Two major earthquakes of Bihar-Nepal border in 1934 and 1988 can explain the impact of earthquake disasters on human structures and human lives. The damage caused by the Bihar earthquake of 15 January, 1934, measuring 8.4 on Richter scale, include 10,700 human deaths, landslides and slumping in an area of 250 km length and 60 km width, ruptures and faults in the ground surface etc. which caused irreparable dam­age to human structures.

The Darbhanga (Bihar) earth­quake of 21 August, 1988 measuring only 6.5 magni­tude on Richter scale (1000 times smaller than the great earthquake of 1934 in intensity) damaged 25,000 houses due to unconsolidated Gangetic alluvium which in fact acted as a seismic amplifier. The disastrous earthquake of Mexico city of 1985 (September) caused total collapse of 400 buildings, damage to 6,000 build­ings and moderate damage to 50,000 buildings.

Be­sides, the infrastructures of the city were seriously damaged, for example, water pipes were broken, tel­ecommunication lines and systems were severely dam­aged, power and water supplies were disrupted, inner vehicular transport was halted etc.

The severe earth­quake of 9 February, 1971 in the San Fernando valley, located to the north-west of Los Angeles (USA) caused total collapse of Olive New Hospital in Sylmar. This damage shocked everybody because this building was constructed in conformity with the earthquake resist­ance standards. Uttar Kashi (Uttaranchal) earthquake of 1991 and Latur-Kilari quake (Maharashtra) of 1993 (India) flattened many buildings.

iii. Damages to the Towns and Cities:

Earthquakes have their worst effects on towns and cities because of highest density of buildings and large agglomerations of human populations. The earth tremors of higher magnitudes shake the ground to such an extent that large buildings collapse and men and women are hurried under large debris and rubbles of collapsed structural materials of buildings, ground water pipes are bent and damaged and thus water supply is totally disrupted, electric poles are uprooted and electric and telephone wires and cables are heavily damaged caus­ing total disruption of electric supply, obstruction and destruction of sewer systems causes epidemics, road blocks throw the transport systems out of gear etc.

Kolkata city was severely damaged due to se­vere earthquake of 11 October, 1737 as thousands of buildings were severely damaged and 3,00,000 people were killed. The sad tale of the destruction of Mexico city due to the earthquake of 1985 has already been described. Recent Bhuj earthquake of Gujarat (Jan. 26, 2001) flattered towns of Anjar and Bhuj destroying more than 90 percent buildings.

iv. Loss of Human Lives and Property:

It may be pointed out that it is not the intensity (magnitude of Richter scale) of earthquake alone which matters more as regards the human casualities but it is the density of human population and houses which matter more in terms of human deaths and loss of property.

For exam­ple, the Kangra earthquake of India in 1905 recorded 8.6 magnitude on Richter scale but it could cause deaths of only 20,000 people whereas 1976 Tang-Shan earthquake of China measuring 7.8 to 8.1 on Richter scale killed 7,50,000 people.

More than 40,000 people lost their lives in the devastating earthquake of Turkey (August 17,1999) which recorded 7.4 on Richter scale. The loss of human lives caused by earthquakes has been enumerated in the preceding section on the clas­sification of earthquakes based on human casualities (see also tables 10.1, 10.2, 10.3).

The strong vibrations caused by se­vere earthquakes strongly shake the buildings and thus strong oscillations cause severe fires in houses, mines and factories because of overturning of cooking gas cylinders, contact of live electric wires, churning of blast furnaces, displacement of other electric and fire- related appliances. For example, the house wives were cooking their lunches in the kitchens when disastrous killer earthquake struck in the vicinity of Tokyo and Sagami Bay in 1923.

Consequently, severe fire broke out which claimed the lives of 38,000 people out of total fatalities of 1,63,000 caused by the earthquake through various processes. This earthquake resulted into total loss of property worth 2,500 million US dollars. The severe earthquake of San Fransisco (USA), which occurred on April 18, 1906, caused widespread fires in several parts of the city.

No water could be made available immediately to extinguish the fire because water pipes were also broken and displaced by the earthquake. Two biggest oil refineries of Turkey were completely devastated due to fire caused by the killer earthquake of August 17, 1999 (7.4).

vi. Deformation of Ground Surface:

Severe earth tremors and resultant vibrations caused by severe earth­quakes result in the deformation of ground surface because of rise and subsidence of ground surface and faulting activity. For example, the Alaska (USA) earth­quake of 1964 caused displacement of ground surface upto 10-15 metres.

The 1897-Assam earthquake caused a large fault measuring 10.6 m (35 feet) wide and 19.3 km (12 miles) long. Several faults were created in the mouth areas of the Mississippi river because of the earthquakes of 1811, 1812 and 1813 in the Mississippi valley. The alluvial-filled areas of the flood plains of the Mississippi were fractured at many places which forced ground surface at few places to collapse. This process resulted in the formation of lakes and marshes.

The ground surface was greatly deformed in the delta area of the Indus River (in Pakistan) due to the earthquake of 1819 as an area of 4,500 square kilome­tres was submerged beneath sea water and this land area disappeared for ever. It may be pointed out that subsidence in one area is followed by emergence of the land in other area.

This also happened in the Indus delta area as a large area measuring 80 km in length and 26 km in width was raised by 3 m from the surrounding area. Similarly, the coastal land of Chile was raised from 6m to 13 m because of the earthquake of 1835. The seafloor of Sagami Bay of Japan was subsided from 305 m to 457 m because of the earthquake of 1923.

vii. Flash Floods:

Strong seismic events result in the damages of dams and cause severe flash floods. Severe floods are also caused because of blocking of water flow of rivers due to rock blocks and debris produced by severe tremors on the hill slopes facing the river valleys. Sometimes, the blockade of the rivers is so immense that even the main course of the river is changed.

The 1950 earthquake of Assam produced barrier in the Dihang river, the tributary of the Brahmaputra River, due to accumulation of huge debris caused by landslides triggered by earth tremors and thus caused severe flash floods in the upstream sec­tions. Similarly, the dam on Subansiri River broke in and resultant flash flood submerged an area of 770 square kilometres.

viii. Tsunamis:

The seismic waves, caused by the earthquakes travelling through sea water, generate high sea waves and cause great loss of life and prop­erty. Since the Pacific Ocean is girdled by the ring of earthquakes and volcanoes tsunamis are more com­mon in the Pacific with a minimum frequency of 2 tsunamis per year. The Kutch earthquake of June 16, 1819 generated strong tsunamis which submerged the coastal areas and inflicted great damage to ships and country-made boats of the fishermen.

The land area measuring 24 km in length was raised upward because of tectonic movement triggered by the said earthquake which provided shelter to the stranded and marooned people. This is why the people called this raised land as Allah’s Bund (bund created by the God). The great tsunamis caused by the Lisbon earthquake of the year 1755 (in Portugal) generated about 12 m high sea waves which damaged most parts of Lisbon city and killed 30,000 to 60,000 people.

The impact of this earthquake was so enormous that the waters of inland lakes like Looh Lomond and Looh Ness continued to oscillate for several hours. The strong tsunamis triggered by Lisbon earthquake also caused 3.5 m to 4.5 m high waves as far away as the West Indies. The earthquake caused by violent volcanic eruption of Karakatoa in 1883 caused enormous tsunamis which generated 36.5 m high sea waves which ravaged the coastal areas of Java and Sumatra and killed 36,000 people.

Tsunami: Historical Perspective:

The waves generated in the oceans triggered by high magnitude earthquakes in the ocean floors (ex­ceeding 7.5 on Richter scale), or by violent central volcanic eruptions, or by massive landslides of the coastal lands or of submerged continental shelves and slopes or in deep oceanic trenches, are called tsunami, which is a Japa­nese word meaning thereby harbour waves.

The tsu­namis are long waves (with longer wavelengths of 100 km or more) which travel at the speed of hundreds of kilometers per hour but are of shallow in depth in deeper oceans and seas. As these waves approach coastal land, the depth of oceanic water decreases but the height of tsunamis increases enormously and when they strike the coast, they cause havoc in the coastal areas.

The best example of tsunami induced by violent volcanic eruption is from Krakatao eruption which occurred in 1883. Severe earthquake caused by Krakatao eruption generated furious tsunami waves ranging in 30 to 40 meters in height (average being 120 feet or 36.5 m). These waves were so violent that they ravaged the coasts of Java and Sumatra and killed 36,000 people.

Since the Pacific Ocean is girdled by conver­gent plate boundaries and the ring of earthquakes and volcanoes, tsunamis are more common in the Pacific with a minimum frequency of 2 tsunamis per year. The great tsunamis caused by the Lisbon earthquake (Por­tugal) of the year 1755 generated about 12 m high sea waves which damaged most parts of Lisbon city and killed 30,000 to 60,000 people.

The Kutch earthquake of June 16, 1819 generated strong tsunamis which submerged the coastal areas. The land area measuring 24 km in length was raised upward because of tectonic movements. The raised land was called as Allah’s Bund (bund created by the God).

The following are the significant tsunamis in the second half of the 20th century and 21st century:

(1) Aleutian tsunami:

April 1,1946, gener­ated by Aleutian earthquake of the magnitude of 7.8 on Richter scale, the resultant tsunami with a height of 35 m killed many people in Alaskan and Hawaiian coastal areas.

(2) Kamchatka tsunami:

Nov. 4,1952, earth­quake of the magnitude of 8.2, generated Pacific-wide tsunami with a wave height of 15 m.

(3) Aleutian tsunami:

March 9, 1957, earth­quake of the magnitude of 8.3 on Richter scale, gener­ated a Pacific-wide tsunami of 16 m height and ad­versely affected Hawaii islands.

(4) Chilean tsunami:

May 22, 1960, a strong earthquake of the magnitude of 8.6 on Richter scale, generated Pacific-wide tsunamis and claimed 2,300 human lives in Chile.

(5) Alaskan tsunami:

March 28,1964, a strong earthquake of the magnitude of 8.4 on Richter scale, generated 15 m high tsunami and killed more than 120 people in Alaska.

(6) Papua New Guirea tsunami:

July 17, 1998, a moderate intensity (7.00n Richter scale) sub­marine earthquake followed by massive submarine landslides generated 30m high tsunami killing thou­sands of people living along the lagoon.

(7) Sumatra tsunami:

December 26, 2004, a powerful earthquake of the magnitude of 9 on Richter scale, off the coast of Sumatra with its epicenter at Simeulue in the Indian Ocean occurred at 00:58:53 (GMT), 7:58:53 (Indonesian Local Time) or 6.28 a.m. (Indian Standard Time, 1ST) and generated a powerful tsunami with a wavelength of 160 km and initial speed of 960 km/hr. The deep oceanic earthquake was caused due to sudden subduction of Indian plate below Burma plate upto 20 meters in a boundary line of 1000 km or even more (2000 km upto southern China).

This tec­tonic movement caused 10 m rise in the oceanic bed which suddenly displaced immense volune of water causing killer tsunami. This earthquake was largest (highest on Richter scale) since 1950 and the 4th largest since 1900 A.D. The Andaman and Nicobar group of islands were only 128 km (80 miles) away from the epicenter (Simeulue) and the east coasts of India were about 1920 km (1200 miles) away from the epicenter.

The furious tsunami with a height of about 10 m adversely affected 12 countries bordering the Indian Ocean; worst affected areas included Tamil Nadu coast and Andman-Nicobar Islands of India, Sri Lanka, Indonesia and Thailand. The strong tsunami took about 3 hours to strike Tamil Nadu coast. The killer tsunami claimed more than200,000 human lives in the affected countries wherein Indonesia, Sri Lanka and India stood 1st, 2nd and 3rd in the number of human casualties.

Japan Tsunami, 2011 :

Date : March, 11, 2011; time : Japan time = 2.46 A. M., 1ST = 6.15 A. M.; undersea earth quake of 8.9 magnitude; epicenter 130 km off the coast of Sendai City near Lameng Village and 380 km north-east of Tokyo, at the depth of 10 km on sea bed; tsunami wave height 10m; more than 10,000 people killed; many cities like Miyako, Miyagi, Kesennuma were flattened; Sendai airport was inundated with heaps of cars, trucks, buses and mud deposits; aircrafts including fighter planes standing on airport were washed out by gushing tsunami waves; rotation speed of the earth increased by 16 microseconds; day length decreased by 1.6 microseconds; Honshu island was displaced by 2.4 m due to monstrous quake; earth rotational axis was displaced by 10 centimeters; 2100 km stretch of eastern coastlines having several villages, cities and towns were battered by killer tsunami; nuclear power plants in Fukushima severely damaged resulting into leakage of killer radiactive radiation; more than 5 lakh people in the radius of 20 km from Fukushima power plants were evacuated and shifted to safer places.

Essay # 5. World Distribution of Earthquakes :

If we look at the world distribution map of earthquakes (fig. 10.2) it appears that the seismic centres are closely related to certain zones of the globe. Earthquakes are, in fact, associated with the weaker and isostatically disturbed areas of the globe.

Most of the world earthquakes occur in:

(i) The zones of young folded mountains,

(ii) The zones of faulting and fracturing,

(iii) The zones representing the junction of continental and oceanic margins,

(iv) The zones of active volcanoes, and

(v) Along different plate bounda­ries.

The world map of the distribution of earth­quakes prepared by the seismologists on the basis of computer analysis and simulation of 30,000 earth­quakes that occurred between 1961 and 1967 very much coincides with the traditional map of world distribution of earthquakes (fig. 10.2) e.g.,

(1) Circum- Pacific Belt surrounding the Pacific Ocean,

(2) Mid- Continental Belt representing epicentres located along the Alpine-Himalayan Chains of Eurasia and northern Africa and epicentres of East African Fault Zones, and

(3) Mid-Atlantic Belt representing the earthquakes located along the mid-Atlantic Ridge and its offshoots. ‘The high-quality seismicity maps showed that narrow belts of epicentres coincide almost exactly with the crest of mid-Atlantic (Ridge).

The east Pacific, and the other oceanic ridges, where plates separate. Earthquake epicenters are also aligned along the transform faults, where plates slide past each other. But the earthquakes that occur at depths greater than about 100 km typically occur near margins where plates collide. It is a basic tenet of the theory of plate tectonics that these deep earthquakes actually define the positions of sub-ducted plates which are plunging back into the mantle beneath an overriding plate.

(1) Circum-Pacific Belt includes the epicentres of the coastal margins of North and South Americas and East Asia representing the eastern and western margins of the Pacific Ocean respectively. This belt accounts for about 65 per cent of the total earthquakes of the world.

This belt presents 4 ideal conditions for the occurrences of earthquakes viz.:

(i) Junction of continental and oceanic margins,

(ii) Zone of young folded mountains,

(iii) Zone of active volcanoes, and

(iv) Subduction zone of destructive or convergent plate boundaries.

The western marginal zones of North and South Americas are represented by Rockies and Andes folded mountain chains respectively. These zones are isostatically very sensitive zones because they are also the zones of convergent plate boundaries where the Pacific Oceanic plate is being continuously subducted below the American plates. Besides, these zones are also the areas of strong volcanic activity.

The earth­quakes associated with the eastern coastal margins of Asia and the island arcs and festoons (Kamchatka, Sakhalin, Japan, Philippines) are caused due to the collision of the Pacific and Asiatic plates and conse­quent vulcanicity. Japan records about 1500 seismic shocks every year.

The recent earthquake of Mexico city in 1985 reveals the impact of collision of convergent (destruc­tive) plate boundaries on the occurrences of earth­quakes. The damage done by the devastating earth­quake included death of 5,000 people, disappearance of 2,000 persons, injuries to 40,000 people, destruc­tion of 4000 buildings, damages to 6,000 buildings, lesser damage to 50,000 buildings etc.

(2) Mid-continental belt is also known as Medi­terranean Belt or Alpine-Himalayan Belt which repre­sents the collision or subduction zones of continental plates. About 21 per cent of the total seismic events of the world are recorded in this belt.

This belt includes the epicentres of the Alpine mountains and their off­shoots in Europe, Mediterranean Sea, northern Africa, eastern Africa and the Himalayan mountains and Bur­mese hills. This belt represents the weaker zones of folded mountains where isostatic and fault-induced earthquakes are caused due to subduction of African and Indian plates below Eurasian plate.

The Indian seismic foci are grouped into 3 zones viz.:

(i) Himalayan region,

(ii) Plain region, and

(iii) Plateau region.

The Himalayan region is a zone of maximum intensity in terms of the magnitude of seis­mic tremors because this zone is located in the subduc­tion zones of the Asiatic and Indian plates where the process of mountain building is still in progress. Uttar Kashi earthquake of October 20, 1991 and Chamoli earthquake of 29 March, 1999 (all in Uttaranchal of India) are latest examples. The plain seismic region is a zone of comparatively moderate intensity.

Even the earthquakes of Assam are also included in this zone. The significant earthquakes recorded in the past in this region are 1934 earthquakes of Bihar, Assam earth­quake of 1950, Kolkata earthquake of 1737 and Darbhanga earthquake (Bihar) of 1988. The peninsular Indian region is considered to be a zone of minimum intensity.

The Indian earthquakes along the Himalayas and foothill zones may be explained in terms of plate tectonics. The Asiatic plate is moving southward whereas the Indian plate is moving northward and hence the northern margin of the Indian plate is being subducted below the Asiatic plate.

The collision of Asiatic and Indian plates and resultant subduction of Indian plate and consequent folding and faulting and gradual rise of the Himalayas at the rate of 50 mm per year cause earthquakes of northern India, Tibet and Nepal.

Ac­cording to J.G. Negi, P.K. Agrawal and O.P. Pandey (as reported in Hindu, September 8, 1988) the Indian subcontinent has deformed at places due to the Indian Ocean floor spreading process. India folds at places and when the energy reaches the elastic limit the rocks break up and trigger strike-slip and thrust fault earth­quakes. The Himalayan fault zone is not actually one fault but a broad system of interactive faults. It consists of a complex grid of faults extending all along this colliding zone.

The earthquake belt extends through Sulaiman and Kirthar shear zones in the west, the Himalayas in the north and Burmese arc in the east. These tectonic events caused by plate movements cause earthquakes in the northern and north-eastern parts of India. Even the earthquakes of Peninsular India have been related to the active faults below deccan traps.

On the basis of magnitude of damage risk India is divided into five damage risk zones:

1. Zone I of least damage risk includes the places of some parts of Punjab and Haryana, plain areas of Uttar Pradesh, portions of plains of Bihar and west Bengal, delta area of the Godavari, coastal plain areas of Maharashtra and Kerala, desert areas of Rajasthan and most areas of Gujarat except Kutch area.

2. Zone II of low damage risk includes southern Punjab and Haryana, southern parts of plains of Uttar Pradesh, eastern Rajasthan, coastal districts of Orissa, Tamil Nadu etc.

3. Zone III of moderate damage risk represents the areas of southern and south-eastern Rajasthan, most of Madhya Pradesh, Maharashtra and Karnataka, southern Bihar(Jharkhand), northern and north-western Orissa etc.

4. Zone IV of high damage risk covers Jammu and Kashmir, Himachal Pradesh, northern Punjab and Haryana, Delhi, eastern Uttar Pradesh, ‘tarai’ and ‘bhabar’ regions and Himalayan regions of Uttaranchal and Bihar and Sikkim areas.

5. Zone V of very high damage risk includes parts of Jammu and Kashmir, some parts of Himachal Pradesh, Uttaranchal, western north Bihar (including Munger-Darbhanga), entire north eastern India and Kutch areas of Gujarat.

Though the plains of west Bengal comes under the zone of least damage risk but the devastating severe earthquake of Kolkata of 11 October, 1737, killing 300,000 people, puts a question mark against this concept. The zone of very high damage risk of Kutch region of Gujarat registered most devastating killer earthquake on Jan. 26, 2001 in its seismic history of past 182 years killing 50,000 to 100,000 people. The epicenter was located near Bhuj town.

Bhuj Earthquake (2001):

While the people of India were busy in celebrat­ing the first republic day on Jan. 26, 2001 of the new century in different parts of the country and the pro­gramme of display of might of armed forces of the country was in progress in New Delhi, the nature demonstrated its might by rocking Kutch region of Gujarat when a severe earthquake struck at 8.45 A.M. and shook the region for almost a minute.

Within no time the villages and towns were flattened, high rise buildings collapsed, many villages and towns became heaps of debris, communication and power lines were completely disrupted, transport system was thrown out of gear and settlements became ruins. This was the second most devastating quake in the earthquake his­tory of India after 1737 killer earthquake of Kolkata (300,000 people dead). The epicentre of this earth­quake was located near Bhuj town (population, 150,000).

A moderate quake measuring 4.2 on Richter scale was registered on 24 December, 2000. The epicentre of this precursor quake was located only 22 km away from Bhuj town but no attention was paid to this precursor seismic event either by experts or by govt., agencies. The Bhuj quake of Jan. 26, 2001 was measured 6.9 on Richter scale by the Indian Meteorological Depart­ment (IMD) while the quake was measured 7.9 which was subsequently upgraded to 8.1 by the U.S.A. France and China.

National Geophysical Research Institute (NGRI) of India and Bhabha Atomic Research Centre (BARC) also confirmed the American measurement (8.1). According to Indian Meteorological Department the main reason for the difference in the magnitude of the quake was the application of different methodolo­gies for the measurement of seismic magnitude by different countries and organizations.

It may be pointed out that the IMD uses body wave for the measurement of seismic magnitude while the USA uses shock waves for this purpose. This severe devastating earthquake killed 50,000 to 100,000 people and adversely affected 5,000,000 people. Bhachau and Anjar towns were totally flattened, 90, 60 and 50 per cent houses collapsed in Bhuj, Rajkot and Ahmedabad respec­tively.

If we look at the past seismic history of Gujarat, it appears that a severe earthquake occurs every 30 years e.g., Bhawnagar earthquake, 1872; Kutch earth­quake, 1903; Dwarka earthquake, 1940; Broach earth­quake, 1970 and Bhuj earthquake, 2001. Between 1845 and 1956 sixty six moderate earthquakes were registered in Kutch area but no one was killed, five severe and one very severe earthquakes rocked the area.

In fact, the sequence of destruction of Kutch began with the severe earthquake of June 19, 1819 (7.1 on Richter scale) when 2000 people were killed, Bhuj town was destroyed, famous mosquake of Ahmedabad was damaged, a 100 km long ridge known as Allah Bund was created (most of which is now in Sind of Pakistan, only 15 km ridge is in India) was formed etc.

The main reasons for the recent Bhuj earth­quake of2001 are: sea floor spreading of Indian Ocean at the rate of 5 cm per year, gradual northward move­ment of Indian plate and reactivated faults below the surface. Two major connecting faults have been lo­cated in Kutch region. A 200 km long and 100 km wide fault runs east-west between Bhuj and Ahmedabad.

The second fault measuring 500 km in length and 100 km in width runs in north-south direction through Ahmedabad, Mehsana and Baroda and is known as Combay Graben. These subterranean faults intersect each other near Viramgam, Santhalpur and Radhanpur towns and become the pivot of seismic events when­ever these are activated due to plate movement.

(3) Mid-Atlantic Ridge Belt includes the epicen­tres located along the mid-Atlantic Ridge and several islands nearer the ridge. This belt records moderate and shallow focus earthquakes which are essentially caused due to the creation of transform faults and fractures because of splitting of plates and their move­ment in opposite directions. Thus, the spreading of sea floor and fissure type of volcanic eruption cause earth­quakes of moderate intensity.

It may be pointed out that the earthquakes that occur along the plate margins (boundaries) are well explained on the basis of plate tectonic theory but the earthquakes originating within the plates are difficult to be explained on the basis of this revolutionary theory.

For example, the earthquakes of New Madrid, Charleston, Boston, Tang-Shan, Koyna etc. are a few examples of intraplate earth­quakes. Similarly, ‘the seismicity of the Indian Shield as revealed from Kutch (1819), Koyna (1967), Bhadrachalam (1969) and Broach (1970) cannot be explained easily by plate tectonics since they occurred away from plate boundary’.

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Earthquakes are some of the most destructive natural disasters. An earthquake consists of rapid vibration of the earth surface. Since its occurrence and enormous capacity is unpredictable by the ordinary human beings, it has been creating fear in human beings since the ancient times. A single shock would last for a few seconds, but when a series of smaller quakes occurs, it could last for about five minutes. It occurs quite frequently across the world but most of the times earthquakes are not very strong to be witnessed by people. However, huge earthquakes have devastating effects. This essay seeks to illustrate the causes and effects of earthquakes.

There are two types of earthquakes: tectonic and volcanic. Tectonic earthquakes occur when the earth is subjected to immense strain making it to eventually move. The earth crust comprises of several plates which float on the mantle. Considering that the plates can move, they can drift apart, towards each other, or slide against each other causing a subduction zone. According to Abrams & Morton (2007), convergent boundaries occur when too much pressure is generated between two plates over a long time. With time, one of the plates bends under the other due to extreme force. As much as the movement is too slow, pressure eventually builds up in the rocks. Eventually an earthquake happens when the pressure can no longer be held by the rocks. The fault ruptures causing the plates to move a long distance in a very short time. The collision triggers large forces in the plates resulting to the occurrence of earthquakes. The best example of a plate tectonic quake is that which occurred in the San Andreas Fault. In this case, the North American plate and the Pacific plate were moving towards the same direction but one was moving faster than the other.

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On the other hand, the volcanic earthquakes are caused by the explosive volcanic eruption. This could either occur at the sea bed or on the land. There are many faults across the world. The location of such faults is a major determinant of where an earthquake will occur because they are the main causes of earthquakes. The type of the fault also determines how often earthquakes occur (Abrams & Morton, 2007). When the earth crust is submitted to tensional forces, it becomes thinner and weak. It causes a hot spot in the mantle which leads the magma to produce pressure and penetrate into the lithosphere and eventually erupt. Earthquakes are triggered by the forceful movement of magma as it finds its way onto the earth surface.

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Earthquakes have various effects including damage to infrastructure, change in geological features and impact on the living things in the areas they occur. Rae (2008) asserts that the rumbling of the earth usually shakes tall buildings, dams and bridges making them fall down. These structures could fall on human beings and animals and kill them or affect the transport system. It becomes very difficult to transport the food, water and health aid to the affected people when bridges are destroyed.

They can also trigger geomorphologic changes. For instance, they could cause the earth crust to move either horizontally or vertically. This could cause a rising, tilting, or dropping of the earth surface and eventually causing landslides or floods. They could also damage gas and power lines and cause fires (Rae, 2008). Additionally, earthquakes that occur in the sea can cause tidal waves or tsunamis: Long and high walls of water travelling at a very high speed. Tsunamis can destroy an entire city or population living next to the coastline. They can also lead to various health effects such as the spread of waterborne diseases that end up killing human beings and animals.

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Earthquakes shake the ground surface, can cause buildings to collapse, disrupt transport and services, and can cause fires. They can trigger landslides and tsunami.

Earthquakes occur mainly as a result of plate tectonics, which involves blocks of the Earth moving about the Earth's surface. The blocks of rock move past each other along a fault. Smaller earthquakes, called foreshocks, may precede the main earthquake, and aftershocks may occur after the main earthquake. Earthquakes are mainly confined to specific areas of the Earth known as seismic zones, which coincide mainly with ocean trenches, mid-ocean ridges, and mountain ranges.

The point of origin of an earthquake is called the focus. The epicentre is the point on the Earth's surface directly above the focus. Most earthquake foci are within a few tens of kilometres of the Earth's surface. Earthquakes less than 70 km deep are classified as shallow-focus. Intermediate-focus earthquakes are 70-300 km deep, and deep-focus earthquakes more than 300 km deep. Shallow-focus earthquakes occur in all of the Earth's seismic zones, but intermediate- and deep-focus earthquakes are almost exclusively associated with seismic zones near ocean trenches.

The destructiveness of an earthquake depends on the size, the depth (shallow ones are more destructive) and the location. Earthquake size can be stated in terms of the damage caused (the intensity) or the amount of ground motion and the energy released by the earthquake (related to the Richter magnitude).

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Geography Gr. 10 Earthquakes and Volcanoes T2 W6

Earthquakes: Case study Volcanoes: Concepts, Characteristics and Location

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Earthquakes & Volcanoes ( CIE IGCSE Geography )

Topic questions.

Study Fig 1, which shows the distribution of earthquakes

State the type of plate boundary at X 

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Study Fig. 3.1, which shows three different types of plate boundary.

Study Fig. 3.1, which shows information about the problems faced by households after an earthquake in Port-au-Prince, Haiti.

Explain why it is necessary to provide clean water and sanitation after an earthquake.

Study Fig. 3.2, which is a diagram of a volcano.

Use labelled arrows to show the following features in Fig. 3.2:

Study Fig. 4.1, which is a cross section through a volcano.

    X ........................................................................................................................................     Y .......................................................................................................................................

Study Fig. 4.2, which shows information about two earthquakes, one which occurred in an MEDC and one in an LEDC.

Describe the differences in the impacts of the earthquakes at Kobe and Port-au-Prince.

Study Fig. 3.1, which shows information about an earthquake.

Study Fig. 3.2, which shows information about two earthquakes which occurred in 2018.

Using information from Fig. 3.2 only, state three reasons why the earthquake in Indonesia caused more deaths and injuries than the earthquake in Venezuela. 1 ....................................................................................................

2 ....................................................................................................

3 ....................................................................................................

Study Fig. 3.1, which shows the Earth’s tectonic plates and their boundaries.

Study Fig. 3.2, which shows information about an eruption of Mauna Loa volcano in Hawaii.

Compare the flow of lava from Mokuaweoweo crater (labelled M on Fig. 3.2) with the flow from Pu’u Ula’ula crater (labelled P ).

Study Fig. 4.1, which is a map of earthquakes in part of South America in the 21 st century.

Study Fig. 4.2, which shows information about how to make a room safer in an earthquake.

Give three ways that Room B is likely to be safer in an earthquake than Room A .

1 .............................................

2 .............................................

3 .............................................

Study Fig. 3.2, which is a map showing information about earthquakes which caused more than 10 000 deaths in different parts of the world (1900-2011).

With reference to a place you have studied, explain how living close to a tectonically active area can have advantages as well as risks 

Explain why an earthquake occurred in a named area you have studied.

Name of area ..............................................

Volcanic eruptions are another tectonic hazard. For a named volcano you have studied, explain the causes of a volcanic eruption. Name of volcano ..................................................

For a named example you have studied, explain the causes of an earthquake.

Name of example ..........................................

For a named volcano you have studied, explain the causes of an eruption. Name of volcano ................................................

For a named area which you have studied, explain the causes of an earthquake . Name of area ..............................

Explain the causes of the eruption of a named volcano. Name of volcano ....................................

Describe the benefits of living near volcanoes.

Explain what can be done to reduce the impacts of eruptions on people who live near volcanoes.

Explain how new buildings can be earthquake-proofed, so that they are less likely to be damaged in an earthquake.

Explain how volcanoes offer opportunities to the people who live close to them.

Explain why the distribution of the areas where large numbers of deaths have been caused by earthquakes is uneven.

Explain why earthquakes of the same magnitude may have different impacts.

Draw a diagram of a strato-volcano (composite cone) in the box below and label its main features.

Explain why more deaths and injuries are caused by earthquakes than by volcanic eruptions.

Explain why many people live in areas where earthquakes occur.

Explain why earthquakes are likely to cause more injuries and deaths than volcanic eruptions.

NASA and the Smithsonian Teach the World about Volcanoes

The Smithsonian Institution dedicates itself to spreading knowledge as far and wide as possible – a goal that aligns quite well with NASA’s mission to help understand Earth's interconnected systems. To further these goals, NASA's Earth Applied Sciences Disasters program area teamed up with the Smithsonian to contribute to the Global Volcanism Program ( GVP ) to teach the public about volcanoes and share Earth-observing data in support of volcano risk reduction, response and recovery. The Smithsonian’s GVP currently contains the world’s most comprehensive catalog of volcanoes and volcanic eruptions, known as the Volcanoes of the World database ( VOTW ), and is trusted worldwide. The GVP’s website is freely accessible and provides viewers with a highly visible platform for education, outreach, and dissemination of global volcanic data.

NASA’s Disasters program and the GVP have been working together to promote volcanic awareness for almost a decade now. In 2012, NASA first supported the GVP through its MEaSUREs program ( Making Earth System Data Records for Use in Research Environments ) to archive the climate data record of volcanic sulfur dioxide (SO2) emissions for past and current GVP-reported eruptions. Then, in 2015, NASA and the Michigan Technological University collaborated with the GVP to add multi-satellite volcanic SO2 emissions data to the VOTW.

In 2016, the GVP launched “ Eruptions, Earthquakes, and Emissions ,” or “E3,” a web application that combines data from the USGS, NASA, and the GVP and provides users with a time-lapse animation of volcanic eruptions and earthquakes since 1960, as well as volcanic SO2 emissions since 1978. Before E3, there was no single available source of global datasets on volcanic emissions, eruptions, and earthquakes in a common format. Now, users can access all this consolidated information online and download data straight from the application, providing a simple and intuitive mechanism for scientists and the public to access the data.

“NASA satellite observations are critical for global volcano monitoring, but while NASA data are publicly available, it can be difficult for the general public to visualize and interact with the data,” explains Nickolay Krotkov, Physical Research Scientist at NASA’s Goddard Space Flight Center and principal investigator of the NASA ROSES A.37 research project " Day-Night Monitoring of Volcanic SO2 and Ash for Aviation Avoidance at Northern Polar Latitudes ." “Hosting NASA's volcanic emissions data in the Smithsonian GVP’s globally recognized VOTW database, including the E3 application, provides a unique opportunity for public engagement with NASA’s products.”

Currently, VOTW hosts NASA volcanic data from NASA’s Ozone Monitoring Instrument ( OMI ), Ozone Mapping and Profiler Suite ( OMPS ), and the TROPOspheric Monitoring Instrument ( TROPOMI ) aboard the ESA Copernicus Sentinel-5 precursor satellite. NASA uses data from these projects to regularly update the GVP database and the E3 application, presenting the Smithsonian with new events and information as they become available.

In 2023, NASA plans to launch a new satellite that will allow for an even more detailed view of the Earth. This satellite, a product of a joint Earth-observing mission with the Indian Space Research Organization ( ISRO ), is known as NISAR (NASA-ISRO Synthetic Aperture Radar), and is predicted to provide the GVP with even more timely volcanic information. Through working with like-minded organizations such as the Smithsonian and ISRO, the NASA Disasters program can share resources and reach a larger audience, thus furthering scientific discovery and public knowledge at the same time. NASA’s collaboration with the Smithsonian is one of many invaluable partnerships that help NASA turn innovation into action.

Learn more about how NASA supports risk reduction, response and recovery for volcanoes.

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Earthquakes and volcanoes

Study and revision resources.

1. Plate Tectonics

Structure of the earth.

The earth consists of 4 main layers:

• The  crust  is the outer layer, broken into sections caled tectonic plates. It is the thinnest layer and the one which we live on.
• The  mantle  is the thickest layer and consists of molten rock
• The  outer core  is molten & about 3000 degrees C.
• This  inner core  is solid due to the immense pressure and is about 5000 degrees C.
• Both the inner & outer core consist of iron & nickle.

Tectonic Plates

Plate Movement

The earths crust is broken into different sections which are slowly moving about.

Convection currents in the mantle distribute the heat from the core. This movement drags the plates in different directions and is responsible for earthquakes and volcanoes.

Over millions of years the land masses that we are familiar with have moved around the planet as the tectonic plates shifted about.

Where the different sections of tectonic plate meet the movement causes geographical features such as mountains, volcanoes and earthquakes.

Constrcutive Boundaries

• Convection currents in the mantle drag the plates apart.
• Magma rises to fill the gap and solidifies to form new crust.
• As the process repeats a ridge is formed and this slowly gets wider as the plates continue to seperate.
• Example: the Mid-Atlantic Ridge.
• This creates fissure volcanoes which are long cracks, they are less explosive.

Destructive Boundaries

• Oceanic & continental plates collide. The oceanic plate is denser and so sinks under the continental plate.
• As the oceanic plate sinks it takes some sand, water and other materia from the sea bed with it. This melts and is gaseous which causes it to force its way up to the surface as a volcano.
• The continental plate crumples at the edge creating fold mountains in addition to the volcanoes.

Collision Boundary

• Convection currents in the mantle pull two plates of continental crust together.
• Since both crusts are made of the same material and have equal density neither subducts. They crumple up.
• This process creates fold mountains. There are no volcanoes at these boundaries but earthquakes occur.
• Example: the Himalayas.

2. Volcanoes

Types of Volcano

• Shield : gentle sloping, created by basic lava (travels along way before solidifying). Found at constructive boundaries.
• Composite : alternating layers of acid lava & rock/ash create the classic conical shape. Found at destructive boundaries.
• Ash & cinder : Alternating layers of ash & cinder compacted.
• Fissure : volcanoes running along a crack in the crust, usually a constructive boundary.
• Caldera : Crater volcano created after volcano collapses in on itself having emptied the magma chamber.
• Dome : steep sided volcano created by acid lava which cools before it has travelled far.
• Destructive boundary volcanoes are often cone shaped and explosive.
• Constructive boundary volcanoes are often more gently sloped and have less violent erruptions.

Volcanic Features

Objective: be able to correctly label the key features of volcanoes and relate them to the increased risk they pose to human settlements.

• Volcanoes vary in shape and structure depending on the reason for their existence.
• Secodary vents (fumaroles) occur when magma and gases force their way through weaknesses in the main volcanic structure.
• Lava, ash, cinders and smoke may be ejected from the vent.
• Draw and label a simple diagram of a volcano and the ejected material.
• Make simple sketch diagrams showing fissure, dome and ash-cinder volcanic structures.
• Using Figure 2.0, describe the location of the Pacific Ring of Fire and explain why this area has this name.

Costs & Benefits of Volcanic Environments

Negative Impacts

• Volcanic eruptions can cause significant damage and loss of life.
• Lava flows destroy vegetation buildings and roads.
• Ash can smother plants, cut out light in the atmosphere, disrupt air travel and cause respiration problems for people.
• Eruptions often cause earthquakes as pressure is released.
• Volcanoes with ice near the peak, or crater lakes can cause devastating mud flows as the water mixes with loose ash.
• Gas released from volcanoes can travel down the slopes silently killing people and animals.

Positive Impacts

• Volcanoes can bring environmental and socio-economic benefits.
• Fertile soils: ash and lava contain many minerals and nutrients that weather to form fertile soils which can be used very effectively for farming.
• Sulphur deposits: sulphur is mined and sold by the people living close to volcanoes in Indonesia.
• Tourism: the volcanic scenery, crater lakes, hot spring and geysers attract tourists and create many job opportunities.

Case Study: Montserrat

Objective: be able to describe the main events and damage caused by the volcano. You should be able to suggest reasons for the extent of the damage.

Montserrat is an island in the Caribbean that unexpectedly suffered devastating eruptions.

• Using the google map shown to the right, describe the location of Montserrat on a regional scale.
• Draw a sketch map showing the location of the Sufriere Hills volcano within the island.
• Explain the cause of the volcano
• Describe the main effects/impacts of the eruptions
• Why did they cause so much damage on the island?
• Make a sketch of Figure 2.1 to show the hazard map and restricted zones that are in place on Montserrat since the eruption.

3. Earthquakes

Earthquake Characteristics

• Focus: the exact point at which the earthquake occurred- often deep in the ground.
• Epicentre: the point on the surface of the earth directly above the focus (so it can be located easily on maps).
• Seismic waves: these are the shockwaves that move outwards from the focus. Their energy disipates the further they travel.
• Seismometer: instrument that measures the magnitude of earthquakes.

Risk factors and Earthquakes

Objective: Demonstrate an ability to to identify factors that can affect the scale of a disaster and be able to link them to levels of development.

• Watch Video 2.1.2
• Describe why older building tend to suffer more damage in earthquakes than newer ones.
• Why do buildings built on soft land suffer more than those with foundations on rock?
• Why can hospitals outside towns add to the problems?

Measuring Earthquakes

• Seismometer: a machine that records vibrations in the earth.
• Seismograph : the print out/graph produced by the seismometer.
• Richter scale : the sale traditionally used to record the magnitude of an earthquake.
• Movement Magnitude Scale: the scale often used currently to record the magnitude of earthquakes (it is more accurate for large earthquakes than the Richter scale.

Case Study: Haiti

Cause & Effect of the Haiti Earthquake

Objectives:

• Understand the cause of the Haiti earthquake.
• Demonstrate an ability to interpret information shown in photographs.
• Demonstrate analytic and reasoning skills in relation to development and disaster impacts.
• Describe the location and cause of the earthquake.
• Go to this page BBC bitesize. Describe the key facts about the damage it caused.

Responses to the Earthquake

• Watch Videos 2.1.3 and 2.1.4
• Go to these links Guardian: Haiti 2015 and Haiti then & now .
• How well has Haiti recovered from the earthquake?
• Describe three reasons why there are still lots of problems in Haiti 5 years on from the earthquake.

Extended Writing Task

Explain why the less developed a country is the more it is likely to suffer if an earthquake occurs. (you should write about a page in your book to answer this. Factors to include: preparation, emergency response, rebuilding/reconstruction.

4. Revision

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Academic literature on the topic 'Volcanoes and earthquakes'

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Journal articles on the topic "Volcanoes and earthquakes":

Seniukov, S., and I. Nuzhdina. "VOLCANOES of KAMCHATKA." Zemletriaseniia Severnoi Evrazii [Earthquakes in Northern Eurasia] , no. 22 (November 12, 2019): 485–501. http://dx.doi.org/10.35540/1818-6254.2019.22.43.

Seniukov, S., and I. Nuzhdina. "VOLCANOES OF KAMCHATKA." Earthquakes in Northern Eurasia , no. 23 (December 15, 2020): 375–87. http://dx.doi.org/10.35540/1818-6254.2020.23.38.

Bagirov, E., R. Nadirov, and I. Lerche. "Earthquakes, Mud Volcano Eruptions, and Fracture Formation Hazards in the South Caspian Basin: Statistical Inferences from the Historical Record." Energy Exploration & Exploitation 14, no. 6 (December 1996): 585–606. http://dx.doi.org/10.1177/014459879601400604.

Kugaenko, Yu A., V. A. Saltykov, I. Yu Koulakov, V. M. Pavlov, P. V. Voropaev, I. F. Abkadyrov, and V. P. Komzeleva. "An Awakening Magmatic System beneath the Udina Volcanic Complex (Kamchatka): Evidence from Seismic Unrest of 2017–2019." Russian Geology and Geophysics 62, no. 2 (February 1, 2021): 223–38. http://dx.doi.org/10.2113/rgg20194098.

Inoue, Hiroshi, Renato U. Solidum, and Jr. "Special Issue on Enhancement of Earthquake and Volcano Monitoring and Effective Utilization of Disaster Mitigation Information in the Philippines." Journal of Disaster Research 10, no. 1 (February 1, 2015): 5–7. http://dx.doi.org/10.20965/jdr.2015.p0005.

Takada, Youichiro, and Yo Fukushima. "Volcanic Subsidence Triggered by Megathrust Earthquakes." Journal of Disaster Research 9, no. 3 (June 1, 2014): 373–80. http://dx.doi.org/10.20965/jdr.2014.p0373.

Kasahara, J. "GEOPHYSICS: Tides, Earthquakes, and Volcanoes." Science 297, no. 5580 (July 19, 2002): 348–49. http://dx.doi.org/10.1126/science.1074601.

Brodsky, E. E., B. Sturtevant, and H. Kanamori. "Earthquakes, volcanoes, and rectified diffusion." Journal of Geophysical Research: Solid Earth 103, B10 (October 10, 1998): 23827–38. http://dx.doi.org/10.1029/98jb02130.

Iguchi, Masato, Surono, Takeshi Nishimura, Muhamad Hendrasto, Umar Rosadi, Takahiro Ohkura, Hetty Triastuty, et al. "Methods for Eruption Prediction and Hazard Evaluation at Indonesian Volcanoes." Journal of Disaster Research 7, no. 1 (January 1, 2012): 26–36. http://dx.doi.org/10.20965/jdr.2012.p0026.

Slattery, William. "Earthquakes, Volcanoes, and the Information Superhighway." Science Activities: Classroom Projects and Curriculum Ideas 33, no. 3 (September 1996): 8–12. http://dx.doi.org/10.1080/00368121.1996.10113226.

Dissertations / Theses on the topic "Volcanoes and earthquakes":

Roberts, Nick Stuart. "Earthquake distributions at volcanoes : models and field observations." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/23653.

Hill-Butler, C. "Evaluating the effect of large magnitude earthquakes on thermal volcanic activity : a comparative assessment of the parameters and mechanisms that trigger volcanic unrest and eruptions." Thesis, Coventry University, 2015. http://curve.coventry.ac.uk/open/items/5f612a7d-ebbf-4d38-90aa-89c4984a1c0f/1.

Woods, Jennifer. "Dyke-induced earthquakes during the 2014-15 Bárðarbunga-Holuhraun rifting event, Iceland." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/289448.

Fuchs, Florian [Verfasser]. "Dynamic triggering: The effects of remote earthquakes on volcanoes, hydrothermal systems and tectonics / Florian Fuchs." Bonn : Universitäts- und Landesbibliothek Bonn, 2015. http://d-nb.info/1077289243/34.

Loureiro, Miguel. "Of the earthquake and other stories : the continuity of change in Pakistan-administered Kashmir." Thesis, University of Sussex, 2012. http://sro.sussex.ac.uk/id/eprint/43284/.

Feng, Lujia. "Investigations of volcanic and earthquake-related deformation: observations and models from Long Valley Caldera, Northwestern Peloponnese, and Northwestern Costa Rica." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41220.

Ratdomopurbo, Antonius. "Étude sismologique du volcan Merapi et formation du dome de 1994." Grenoble 1, 1995. http://www.theses.fr/1995GRE10064.

Hidayati, Sri. "Study on volcano-tectonic earthquakes at Sakurajima volcano and its surroundings." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136776.

Bracamontes, Dulce Maria Vargas. "Stress models related to volcano-tectonic earthquakes." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540585.

Jeddi, Zeinab. "Seismological Investigation of Katla Volcanic System (Iceland) : 3D Velocity Structure and Overall Seismicity Pattern." Doctoral thesis, Uppsala universitet, Institutionen för geovetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303342.

Books on the topic "Volcanoes and earthquakes":

Knight, Linsay. Volcanoes & earthquakes . Edited by Moores Eldridge M. 1938-, Beckett Andrew, and National Geographic Society (U.S.). [Alexandria, Va.]: Time-Life Books, 1996.

Rubin, Ken. Volcanoes & earthquakes . Dorking: Templar, 2008.

Knight, Linsay. Volcanoes & earthquakes . Edited by Moores Eldridge M. 1938-. Hemel Hempstead: Macdonald Young Books, 1995.

Vrbova, Zuza. Volcanoes & earthquakes . Mahwah, N.J: Troll Associates, 1990.

Kerrod, Robin. Volcanoes & earthquakes . London: Hermes House, 2000.

Oxlade, Chris. Earthquakes & volcanoes . London: Franklin Watts, 2006.

Stidworthy, John. Earthquakes & volcanoes . San Diego, CA: Thunder Bay Press, 1996.

Lauber, Patricia. Volcanoes and earthquakes . New York: Scholastic, 1985.

Booth, Basil. Earthquakes and volcanoes . London: Cloverleaf, 1992.

Jennings, Terry J. Volcanoes and earthquakes . Parsippany, N.J: Silver Burdett Press, 1998.

Book chapters on the topic "Volcanoes and earthquakes":

Wang, Chi-Yuen, and Michael Manga. "Mud Volcanoes." In Lecture Notes in Earth System Sciences , 323–42. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-64308-9_12.

Wang, Chi-Yuen, and Michael Manga. "Mud Volcanoes." In Earthquakes and Water , 33–43. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00810-8_3.

Polet, J., and H. Kanamori. "Tsunami Earthquakes." In Complexity in Tsunamis, Volcanoes, and their Hazards , 3–23. New York, NY: Springer US, 2021. http://dx.doi.org/10.1007/978-1-0716-1705-2_567.

Wright, J. B. "Introduction: earthquakes, volcanoes and meteorites." In Geology and Mineral Resources of West Africa , 151–53. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-015-3932-6_17.

Donovan, Amy. "Earthquakes and Volcanoes: Risk from Geophysical Hazards." In Handbook of Risk Theory , 341–71. Dordrecht: Springer Netherlands, 2012. http://dx.doi.org/10.1007/978-94-007-1433-5_14.

Wang, Kelin, Yan Hu, and Jiangheng He. "Wedge Mechanics: Relation with Subduction Zone Earthquakes and Tsunamis." In Complexity in Tsunamis, Volcanoes, and their Hazards , 55–69. New York, NY: Springer US, 2009. http://dx.doi.org/10.1007/978-1-0716-1705-2_590.

Prost, Gary L., and Benjamin P. Prost. "Acts of God? Earthquakes, Volcanoes, and Other Natural Disasters." In The Geology Companion , 257–314. Boca Raton : CRC Press, 2017.: CRC Press, 2017. http://dx.doi.org/10.1201/9781315152929-12.

Lee, William H. K. "Complexity in Earthquakes, Tsunamis, and Volcanoes, and Forecast, Introduction to." In Encyclopedia of Complexity and Systems Science , 1213–24. New York, NY: Springer New York, 2009. http://dx.doi.org/10.1007/978-0-387-30440-3_80.

Lee, William H. K. "Complexity in Earthquakes, Tsunamis, and Volcanoes, and Forecast, Introduction to." In Extreme Environmental Events , 68–78. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-7695-6_7.

Siegel, Frederic R. "Damping the Dangers from Tectonics-Driven (Natural) Hazards: Earthquakes and Volcanoes." In Mitigation of Dangers from Natural and Anthropogenic Hazards , 19–20. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-38875-5_6.

Conference papers on the topic "Volcanoes and earthquakes":

Yousuke Miyagi, Masanobu Shimada, Takeo Tadono, Osamu Isoguchi, and Masato Ohki. "ALOS emergency observations by JAXA for monitoring earthquakes and volcanic eruptions in 2008." In 2008 Second Workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST) . IEEE, 2008. http://dx.doi.org/10.1109/userest.2008.4740357.

Losik, Len. "Using Satellites to Predict Earthquakes, Volcano Eruptions, Identify and Track Tsunamis." In AIAA SPACE 2012 Conference & Exposition . Reston, Virigina: American Institute of Aeronautics and Astronautics, 2012. http://dx.doi.org/10.2514/6.2012-5176.

Almasi, Amin. "Gravity measurement from moving platform by Kalman Filter and position and velocity corrections for earth layer monitoring to earthquake and volcano activity survey." In 2008 Second Workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST) . IEEE, 2008. http://dx.doi.org/10.1109/userest.2008.4740355.

Firmansyah, Rizky, Andri Dian Nugraha, and Kristianto. "Micro-earthquake signal analysis and hypocenter determination around Lokon volcano complex." In NATIONAL PHYSICS CONFERENCE 2014 (PERFIK 2014) . AIP Publishing LLC, 2015. http://dx.doi.org/10.1063/1.4915048.

Losik, L. "Using satellites to predict earthquakes, volcano eruptions, identify and track tsunamis from space." In 2012 IEEE Aerospace Conference . IEEE, 2012. http://dx.doi.org/10.1109/aero.2012.6187030.

Siregar, Azhar Fuadi, Irwan Meilano, Dina Anggreni Sarsito, and Estu Kriswati. "Correlation between seismic activity and volcano deformation on Sinabung Volcano in February 2017." In INTERNATIONAL SYMPOSIUM ON EARTH HAZARD AND DISASTER MITIGATION (ISEDM) 2017: The 7th Annual Symposium on Earthquake and Related Geohazard Research for Disaster Risk Reduction . Author(s), 2018. http://dx.doi.org/10.1063/1.5047375.

Harlianti, Ulvienin, Andri Dian Nugraha, and Novianti Indrastuti. "Relocation of volcano-tectonic earthquake hypocenter at Mt. Sinabung using double difference method." In INTERNATIONAL SYMPOSIUM ON EARTH HAZARD AND DISASTER MITIGATION (ISEDM) 2016: The 6th Annual Symposium on Earthquake and Related Geohazard Research for Disaster Risk Reduction . Author(s), 2017. http://dx.doi.org/10.1063/1.4987092.

Santoso, Nono Agus, Rahmat Fajri, and Satria Bijaksana. "Identifying volcanic ash through magnetic parameters: Case studies of Mount Sinabung and other volcanoes." In INTERNATIONAL SYMPOSIUM ON EARTH HAZARD AND DISASTER MITIGATION (ISEDM) 2017: The 7th Annual Symposium on Earthquake and Related Geohazard Research for Disaster Risk Reduction . Author(s), 2018. http://dx.doi.org/10.1063/1.5047324.

Ry, Rexha V., A. Priyono, A. D. Nugraha, and A. Basuki. "Seismicity study of volcano-tectonic in and around Tangkuban Parahu active volcano in West Java region, Indonesia." In THE 5TH INTERNATIONAL SYMPOSIUM ON EARTHHAZARD AND DISASTER MITIGATION: The Annual Symposium on Earthquake and Related Geohazard Research for Disaster Risk Reduction . Author(s), 2016. http://dx.doi.org/10.1063/1.4947372.

Fathurrohmah, Septiana, and Ayu Candra Kurniati. "Disaster vulnerability assessment of Merapi Volcano eruption." In INTERNATIONAL SYMPOSIUM ON EARTH HAZARD AND DISASTER MITIGATION (ISEDM) 2017: The 7th Annual Symposium on Earthquake and Related Geohazard Research for Disaster Risk Reduction . Author(s), 2018. http://dx.doi.org/10.1063/1.5047291.

Reports on the topic "Volcanoes and earthquakes":

Syracuse, Ellen Marie. 2005 and 2008 earthquake relocations at Akutan Volcano . Office of Scientific and Technical Information (OSTI), November 2015. http://dx.doi.org/10.2172/1226895.

Earthquakes & Volcanoes, Volume 23, Number 6, 1992 . US Geological Survey, 1993. http://dx.doi.org/10.3133/70039050.

This dynamic planet: World map of volcanoes, earthquakes, impact craters and plate tectonics . US Geological Survey, 2006. http://dx.doi.org/10.3133/i2800.

Earthquakes & Volcanoes, Volume 21, Number 1, 1989: Featuring the U.S. Geological Survey's National Earthquake Information Center in Golden, Colorado, USA . US Geological Survey, 1989. http://dx.doi.org/10.3133/70039068.

Publications of the Branch of Engineering Seismology and Geology, Office of Earthquakes, Volcanoes, and Engineering: January 1980 through December 1985 . US Geological Survey, 1985. http://dx.doi.org/10.3133/1666.

The Response of Taupō Volcano to the M7.8 Kaikōura Earthquake

• Schuler, J.
• Hreinsdóttir, S.
• Illsley-Kemp, F.
• Townend, J.
• Villamor, P.

Several studies suggest that large earthquakes (M > 7.0) can act as external triggers of volcanic unrest, and even eruption. This triggering is attributed to either ground shaking (dynamic stresses) or to permanent ground deformation (associated with static stress changes). However, large earthquakes are rare and testing triggering hypotheses has proven difficult. We use geodetic data to show that the 13 November 2016 Kaikōura earthquake (M w 7.8) triggered local deformation of up to 11 mm at Taupō volcano, 500 km away, which lasted for approximately twelve days. Using elastic geodetic models, we infer that the observed deformation was caused by either aseismic fault slip or a dike intrusion. We then use strong motion data from the surrounding area to show that the Kaikōura earthquake caused maximum dynamic stress changes in the range of 0.15-0.9 MPa in the vicinity of Taupō volcano and conclude that these dynamic stress changes triggered local faulting or dike activity and the associated deformation at Taupō volcano.

• New Zealand;
• volcano-tectonic;

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Io’s volcanoes have been erupting for billions of years

• Jupiter’s rocky moon Io is the most volcanically active world in the solar system. It has hundreds of volcanoes, some with erupting lava fountains dozens of miles (kilometers) high.
• Io’s volcanoes have been active for billions of years , a new study says, ever since Io first formed.
• How do they know? The researchers studied the ratio of different light and heavy sulfur isotopes in Io’s thin atmosphere. The results suggest the volcanoes’ age, and also provide clues about how much sulfur Io has lost since its formation.

Jupiter’s moon Io is famous for the hundreds of volcanoes dotting its surface. It’s the most volcanically active world in our solar system. But how long has Io had its active volcanoes? Researchers at the California Institute of Technology (Caltech), New York University and NASA’s Goddard Space Flight Center said on April 18, 2024, that Io’s volcanoes have been erupting for billions of years, since just after the little moon 1st formed, along with our sun, Jupiter, Earth and the rest of our solar system.

The conclusions are based on new analysis of sulfur in Io’s thin atmosphere. That makes sense, because sulfur plays a key role on Io’s surface and in its atmosphere. Some of Io’s volcanoes spew sulfur and sulfur dioxide in great plumes extending miles (kilometers) above Io’s surface. Extensive plains of sulfur lie in a frosty coating on most of Io’s surface.

If you could stand on Io without a spacesuit (not literally possible since Io is bathed in extreme radiation from Jupiter), you’d find it smells like rotten eggs, due to its sulfur. Now that sulfur has provided clues to the history of Io’s active volcanoes.

The researchers published their peer-reviewed findings in two new papers on April 18, one in Science and the other in JGR Planets .

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New analysis of sulfur isotopes from Io’s volcanoes

So, Io’s volcanoes emit a lot of sulfur. And Io’s atmosphere is 90% sulfur dioxide. The research team conducted an analysis of isotopes of Io’s atmospheric sulfur. This provided clues as to how long Io has been in orbital Laplace resonance with two other moons: Europa and Ganymede.

In other words, Io completes four orbits of Jupiter for every two orbits of Europa and one orbit of Ganymede. As a result, the moons all pull on each other gravitationally. This causes their orbits to be elliptical rather than circular. And in turn, Jupiter’s strong gravity then heats the interiors of the moons. This is why Europa and Ganymede have subsurface oceans and Io has magma and volcanism.

By analyzing the isotopes, scientists could tell how long Io has been in orbital resonance and, therefore, volcanically active. To do this, they used the Atacama Large Millimeter/submillimeter Array ( ALMA ) telescope in Chile.

The sulfur atoms on Io have various isotopes. That is, they have varying numbers of neutrons . Sulfur-32 and sulfur-34 both have 16 protons , but the first has 16 neutrons, while the second has 18. The more neutrons an atom has, the heavier it is. On Io, the heaviest sulfur atoms are at the bottom of the atmosphere, while the lightest are near the top.

Ever-changing surface and atmosphere

Even though Io overall is billions of years old, just like all the other bodies in the solar system, its surface is only about a million years old. This is because its surface is always being replenished by new material from its numerous volcanoes.

Io’s atmosphere is always changing, too. Collisions with charged particles in Jupiter’s magnetic field strip away the already-thin atmosphere into space. This happens at a rate of one ton per second. Therefore, the lighter sulfur isotope at the top of the atmosphere, sulfur-32, gets depleted faster. By calculating how much sulfur-32 is missing, the researchers can determine how long Io has been volcanically active.

This animation is an artist’s concept of Loki Patera , a lava lake on Io, made by using data from the JunoCam imager onboard NASA’s Juno spacecraft. With multiple islands in its interior, Loki is a depression filled with magma and rimmed with molten lava. Video via NASA/ JPL-Caltech/ SwRI/ MSSS/ YouTube .

Sulfur ratios

The researchers looked at the ratio of sulfur-32 to sulfur-34 in Io’s atmosphere. In the early solar system, the ratio was about 23 atoms of sulfur-32 for every one atom of sulfur-34. That ratio is the same today for any body that has remained unchanged since it first formed. But that’s not the case with Io. By far, most of its original sulfur – 92 to 99% – has been lost. Even though so much of the original sulfur – the lighter isotope sulfur-32 in particular – has been lost, this also shows Io must have been volcanically active since soon after its formation.

And that, in turn, shows Io has been in a Laplace orbital resonance with Europa and Ganymede for just as long.

History of Io’s volcanoes

While the new findings show Io has always been volcanically active, there are still various possible specific scenarios for the history of the moon. This includes the possibility that Io was once even more volcanically active early on than it is now. As Ery Hughes , formerly from Caltech and co-author of the first paper in Science , explained :

Because lots of the light sulfur is missing, the atmosphere we measure today is relatively ‘heavy’ in terms of sulfur. Key to achieving such heavy sulfur in Io’s atmosphere is the process of burying the heavy sulfur back into Io’s interior, so that it can be released by volcanoes over and over again. Our modeling shows that sulfur gets trapped in the crust of Io by reactions between the sulfur-rich frosts, which are deposited from the atmosphere and the magma itself, allowing it to be eventually buried into Io’s interior.

On April 18, 2024, NASA also released new video animations of a lava lake and steeple-like mountain on Io. Check them out!

Bottom line: A new study reveals Io’s volcanoes have been erupting for billions of years, ever since the small moon of Jupiter first formed.

Source: Isotopic evidence of long-lived volcanism on Io

Source: Using Io’s Sulfur Isotope Cycle to Understand the History of Tidal Heating

Via Caltech

Read more: Jupiter’s moon Io as you’ve never seen it

Read more: Jupiter’s moon Io: Global magma ocean, or hot metal core?

Paul Scott Anderson

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Kilauea Volcano Erupts on Hawaii’s Big Island

The volcano erupted three times in 2023. There did not appear to be any immediate danger to residents on Monday.

By Victor Mather

Kilauea, the most active volcano in Hawaii, began erupting early on Monday morning. Kilauea, in the southeast part of the Big Island, erupted three times last year.

Because the eruption was happening near the summit, there did not appear to be any immediate danger to residents.

The eruption began at 12:30 a.m. local time. Magma was rising from beneath the surface and “fountaining” up through cracks, the United States Geological Survey said.

Rather than the hundreds of feet you might expect in a classic, major volcanic eruption , Michael Poland, a geophysicist with the U.S.G.S., said the lava at Kilauea was rising only “tens of feet” on Monday.

In 2023, Kilauea erupted in January , June and September . A major eruption in 2018 destroyed 700 homes.

“From 1983 to 2018, all of the activity came from two vents,” Mr. Poland said. “Since 2018, it has gone away from a period of steady eruptions. Now it has discrete, usually shortish eruptions happening in several different places. Now we’re getting eruptions happening in places we haven’t seen in 50 years.”

Recent eruptions have typically lasted six to eight hours.

“Unlike 2018, when lava was coming out in people’s backyards, these are in the national park,” Mr. Poland said, referring to Hawaii Volcanoes National Park.

The volcano alert level was raised Monday to a warning from a watch, the normal move when an eruption starts.

Scientists had been watching for an eruption after about 250 earthquakes were recorded beneath Kilauea’s summit over an eight-hour period before the eruption.

Earthquakes are sometimes a precursor to eruption. The strongest quake was a magnitude-4.1 temblor at 9:12 p.m., about three hours before the eruption.

The U.S.G.S. said that during Kilauea’s eruptions, volcanic gas, including sulfur dioxide, is released. That gas reacts in the atmosphere to create volcanic smog, or vog.

“Vog creates the potential for airborne health hazards to residents and visitors, damages agricultural crops and other plants, and affects livestock,” the agency said.

“It’s more of an irritant,” Mr. Poland said. “If people have sensitive breathing or respiratory issues, they may find it more difficult to breathe.”

Mr. Poland said after the initial eruptions, the activity was starting to wane as of 11 a.m. Eastern time. “We wouldn’t expect this one to be a terribly long-term eruption,” he said.

Victor Mather , who has been a reporter and editor at The Times for 25 years, covers sports and breaking news. More about Victor Mather

Hawaii's Kilauea volcano erupts in remote summit region

A geologist with the u.s. geological survey said the eruption did not pose an immediate threat to residents..

The Kilauea volcano on Hawaii's Big Island erupted on Monday following hours of seismic activity below the volcano's summit, the U.S. Geological Survey said.

Kilauea , one of the world's most active volcanoes, began erupting at approximately 12:30 a.m. local time, about a mile south of Kilauea caldera within Hawaii Volcanoes National Park, a popular tourist destination that draws more than 1 million visitors per year. Webcam footage showed lava spewing from fissures in the summit, the USGS said .

Katie Mulliken, a geologist with the USGS Hawaiian Volcano Observatory, told USA TODAY the eruption poses no immediate danger to residents as it, so far, has been contained to a remote part of the summit, which is inaccessible by car or trails.

"There are really no threats to any communities," Mulliken said, adding that the USGS will continue to closely monitor the volcanic activity.

It was the first eruption in this region of the volcano in almost 50 years. The last one, in December 1974, lasted about six hours.

The USGS Hawaiian Volcano Observatory on Monday raised the volcano alert level for ground-based hazards to a warning, meaning a hazardous eruption "is imminent, underway, or suspected." Further, the USGS issued a red aviation color code, which indicates a "significant emission of volcanic ash" is likely, suspected or imminent, according to the U.S. Geological Survey .

The alerts came after hours of escalating activity beneath the surface of Kilauea. On Sunday, around 400 earthquakes were recorded below Kilauea's summit, with the largest temblor reaching a 4.1 magnitude, Mulliken said. Seismic activity is common before eruptions and is an indicator of lava movement inside the volcano, she added.

The primary hazard of Kilauea eruptions is a high level of volcanic gas because of its potential effects downwind, the USGS said. Other significant hazards includes instability, ground cracking and rockfalls that can be made worse by earthquakes near the summit.

More: After the Hawaii volcano eruption, Hawaii residents struggle to recover

Authorities with the National Forest Service closed an area surrounding the volcano, citing "seismic unrest." Officials also closed the parking lot for the Devastation Trail, which takes hikers through a winding path that offers vistas of land still recovering from the volcanoes 36-day eruption in 1959.

Kilauea erupted three times last year, bringing more than 10,000  tourists to Hawaii Volcanoes National Park to see the fountains of lava. In 2018, the volcano erupted for three months straight, destroying more than 700 structures, including 200 homes on Big Island, and displacing some 3,000 people – many of whom were unable to return home over a year after the eruption.