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Introduction to volcanoes


About 13.8 billion years ago, a ‘Big Bang’ unleased an immense amount of energy and matter which marked the beginning of our universe. Some 4.6 billion years ago in a galaxy called the Milky Way, gravity pulled gases together which resulted in the formation of the Sun. Within a few million years, most of the rock and ice surrounding the Sun accreted into small planets. The third planet from the Sun became Earth. As rocks smashed into the early Earth, the planet accreted even more. The energy from the impact of rocks smashing into Earth converted into heat that caused the planet to melt. At this point, Earth was a ball of soft hot rock.


With the planet melting, the heaviest metals, mainly iron and nickel sank to the centre of Earth to make up the inner core. As accretion slowed down, Earth began to cool. Most of its rock solidified, forming a series of layers around the still-hot metal core. The inner core was surrounded by the outer core, which is then surrounded by the mantle, Earth’s largest layer. Heat from the Earth’s core resulted in the complete melting of the upper mantle turning it into a magma ocean. As Earth cooled further, the magma ocean began to solidify and create a primordial crust made of basalt. This happened some 4.4 billion years ago, between the Hadean and Archean Eons.


Strictly speaking, volcanoes are cracks, or vents in the Earth’s crust through which molten rock, lava, and gases erupt. Boiling magma in the mantle created openings in the Earth’s crust through which, carbon dioxide and water vapour erupted to create the atmosphere. This is known as volcanic outgassing, and the process continues today. By 4 billion years ago, the water vapour condensed to liquid, raining out to form the oceans that would hide Earth’s primordial crust. The Earth might have looked something like a global Indonesia, with volcanic arcs emerging from the oceans, but very few continent-like masses.


The Earth’s crust is connected to the uppermost part of the mantle – this is known as the lithosphere. The lithosphere is divided into seven major and eight minor rigid slabs called tectonic plates that float on the semi-molten mantle below. This is known as tectonic plate theory, and the tectonic processes, slab pull, and ridge push explain how our continents move and how volcanoes form. All volcanoes are formed from igneous rock that originally lay deep underground, where it melted to become magma. When the magma is forced to the Earth’s surface through cracks, or vents, it erupts as lava. Once cooled, the lava forms layers of hard rock that build up to create the conical shape of the volcano.


Most volcanoes on land are stratovolcanoes, or composite volcanoes. They accumulate in height from alternating layers of ash and lava. Before an eruption, magma accumulates to form a magma chamber beneath the volcano. Magma rises to the surface through a central shaft known as the main vent. Magma erupts as lava out of the mouth of the main vent – this is called the crater. Magma can also rise through secondary vents and erupt as lava out of the sides of the volcano, resulting in a side cone.


The majority of volcanoes form along destructive and constructive plate margins, but volcanoes can also erupt through continental crust at hotspots like Hawaii.

Formation of volcanoes


The Earth’s surface is a mosaic of interacting rigid tectonic plates made up of the crust and uppermost part of the mantle, which together form the lithosphere. Plate tectonics is the main driver of pretty much all Earth’s surface processes, especially volcanism. Volcanoes occur along most, but not all, tectonic plate margins, the point at which two plates meet. The majority of volcanoes form along destructive and constructive plate margins, but volcanoes can also erupt through continental crust at hotspots like Hawaii.


Volcanoes erupt for different reasons, and this results in different types of volcanoes. Going back to plate tectonics, we know that the main driver of their movement is slab pull. Denser (heavier) oceanic crust sinks beneath continental crust and creates a destructive plate margin. This pulls oceanic crust apart and creates a constructive plate margin. There is no supply of magma at conservative margins.


To understand how volcanoes form at constructive plate margins, we need to consider the structure of Earth. Inside the Earth, the mantle is not liquid. Although extremely hot with temperatures varying between 1000°C at its boundary with the crust and 4000°C at its boundary with the outer core, intense pressure keeps the mantle mostly solid, or semi-molten – a bit like fudge. At ocean ridges such as the Mid-Atlantic Ridge, two plates are pulled apart creating a rift. As young oceanic crust is pulled apart and stretched, friction with the mantle results in shallow earthquakes of typically low magnitude. With a crack, or vent created the pressure that keeps the mantle solid is relaxed. This allows hot mantle rock to rise but as it does, the drop in pressure causes it to melt and erupt as lava. Once cooled, the lava here solidifies to create new oceanic crust leading to a process known as seafloor spreading. The lava erupting here is basaltic and high in silica, it has low viscosity (the state of being thick) and so spills out over a wide area preventing it from building a steep cone. Instead, continuous eruptions through a main vent causes the growth of a volcano with a wide base, and gentle slopes. The volcanoes at constructive plate margins resemble an upside-down bowl or warriors shield, hence why they are called shield volcanoes.


Over at destructive plate margins where the denser oceanic crust is sinking beneath continental crust, a subduction zone and ocean trench occur. As the two tectonic plates collide, the continental crust is crumpled and folded upwards creating impressive mountain ranges such as the Andes along the east coast of Southern America. As the oceanic plate subducts back into the mantle, it carries with it water from the oceans. The water changes the composition of the hot mantle rock, making it melt. This produces andesite magmas, that are high in viscosity (very thick). The andesite magma rises through a main vent in the overriding continental crust to form volcanic arcs like those surrounding the Pacific plate – where 75% of the world’s active volcanoes are. These volcanoes are more explosive than shield volcanoes and lava and ash build up a tall cone with steep slopes. It is the variety of the erupted material that provides the word ‘composite’ in the name. Although, they are also referred to as stratovolcanoes.


Some volcanoes occur away from destructive and constructive plate margins. These volcanoes are called hotspots are the result of crust moving over stationary plumes of rising hot rock in the mantle.

Volcanic hazards


Different types of volcanoes erupt differently. For instance, shield volcanoes erupt mainly lava flows whereas composite, or stratovolcanoes erupt lava and ash. Sometimes, volcanoes can kill people with erupting any ash or lava at all.


Lava flows are streams of molten rock that ooze from an erupting vent. Lava flows can destroy everything in their path, burying farmland, igniting trees and buildings, and people and animals in the way will perish. However, lava moves relatively slowly because it cools rapidly in contact with air so there is usually time to get out of the way. More people have died from lava flows because they have lingered around watching them for too long or rescuing belongs than have been killed while attempting to flee. At shield volcanoes, the lava is basaltic and mainly silica so is low in viscosity. This makes the lava advance faster than andesite lava that erupts from composite, or stratovolcanoes. It still does not move that fast though, because shield volcanoes are generally flat with gentle slopes.


Perhaps the deadliest hazard during an eruption is a pyroclastic flow. Pyroclastic comes from the Greek words ‘πῦρ’, which means fire, and ‘κλαστός’, which means broken into pieces. Pyroclastic flows are a mix of burning rocks, ash, and gases that advance at speeds over 100mph down the volcanoes slope. They often happen when a lava dome collapses. Lava domes are circular mound-shaped bumps that occur when viscous lava erupts slowly. Pyroclastic flows are more common at composite, or stratovolcanoes than shield volcanoes. You might have learnt about Mount Vesuvius in Naples, Italy and its famous eruption in 79 AD (the same time the Romans founded Mamucium, now Manchester). More recently, in 2018, Volcan de Fuego (Spanish for Volcano of Fire) erupted in Guatemala, Central America. The eruption caused a pyroclastic flow that affected 1.7 million people and killed 165.


Ash clouds occur when fine particles of ash can be blasted many kilometres in the atmosphere. In 1991, Mount Pinatubo in the Philippines erupted and sent an ash cloud 40km into the atmosphere. Most ash falls on the slopes of the volcano and adds to the shape, but winds can pick it up causing it to travel fare from its source. The ash and sulphur dioxide from the 1991 eruption circulated Earth in three weeks and blocked out the Sun’s rays causing a global drop in temperature of 0.5°C. Ash can disrupt air transport as fine particles can damage engines. In 2010, Iceland’s Eyjafjallajökull volcano erupted and air travel across Europe was grounded. Moreover, when ash falls it can smother farmland, suffocate, and poison livestock and damage agricultural machinery. A thick layer of ash can make roofs collapse.


Other hazards include Lahars and volcanic bombs. Lahar is an Indonesian word for streams of hot or cold water mixed with rock. They are sometimes referred to as mudflows. Pyroclastic flows can sometimes generate lahars when heavy rain or snow melt mixes with the debris. They are very fast and difficult to escape. Volcanic bombs are chunks of molten rock flung into the air, where they cool before falling to the surface. They can hit people and cause damage to cars and buildings.


Volcanoes erupt gases such as carbon dioxide which can impact Earth’s climate. We know this was important to the formation of Earth’s early atmosphere. They can also emit large quantities of sulphur dioxide that reacts with water vapour to create a volcanic aerosol that reflects the Sun’s rays. Furthermore, sulphur dioxide is irritating to the eyes, skin and respiratory system.

Volcanic eruption at Mount Nyiragongo, DRC, 2002


Volcanism in Africa is largely driven by the East African Rift Valley, where the African and Arabian tectonic plates are being pushed and pulled apart, creating one of few constructive plate margins that involve continental crust. The EARV is over 4000 miles long and stretches from Djibouti, Eritrea, and the Gulf of Aden through Ethiopia, Kenya, Uganda, Tanzania, Malawi, and Mozambique. Eventually, the African tectonic plate will become two tectonic plates separated by the EARV and the valley will become deep enough for the Indian Ocean to flood it.


The EARV is dotted by extinct, dormant, and active shield and composite, or stratovolcanoes. An extinct volcano like Mount Kenya is a volcano that has not erupted for over 1,000,000 years and is unlikely to ever erupt again. A dormant volcano like Mount Kilimanjaro in Tanzania is a volcano that has not erupted for 10,000 years but could become active again. Mount Nyiragongo is a stratovolcano in the Democratic Republic of Congo – it is very active. Mt. Nyiragongo is one of very few volcanoes that has a permanent lava lake within its crater. This makes the volcano particularly dangerous, and the lava is unusually low in silica and viscosity for a stratovolcano. In 1977, a lava lake drained through fissures (cracks) in the crater in less than one hour and lava flowed down the steep slopes at speeds of 60mph. This killed 70 people, although some reports suggest the number was closer to 2,000.


In 2002, Mount Nyiragongo erupted again in the same way as it did in 1977, and again people received little warning. The eruption lasted less than 12 hours. Some residents reported to BBC news that they did not know what an eruption was, and some people moved closer to the volcano to investigate. Just like earthquakes, volcanic eruptions have primary and secondary effects and immediate and long-term responses.


The primary effects included:

  • 14 nearby villages were destroyed by lava flows.
  • Lava flows covered 15% of the city of Goma including one of the runways at Goma’s airport.
  • 12,500 homes were destroyed by ash and lava.
  • An estimated 170 people died from poisonous gases, collapsed buildings and some become trapped by lava when they returned to their homes to collect belongings.

Secondary effects included:

  • Several earthquakes followed the eruption, some with a magnitude above.
  • An outbreak of cholera in overcrowded refugee camps. Many people left the UN refugee camps and returned to the Democratic Republic of Congo.
  • Many businesses were destroyed which resulted in high unemployment.
  • Poisonous gases caused acid rain which affected farmland and cattle.
  • The acid rain contaminated water used for drinking.
  • About 350,000 people were dependent on aid.


Immediate responses included:

  • 400,000 people were evacuated, and many headed to nearby Rwanda. The UN set up camps for them.
  • The UK sent 33 tonnes of water purification kits to provide clean water for 50,000 people.

Long-term responses included:

  • In 2002, only one scientist monitored the volcano. More scientists were employed to monitor the volcano after. It is now monitored 24 hours a day, 365 days a year.
  • Volcanology is now taught in schools. The population is more aware of the risks than before.


In May 2021, the volcano erupted again, and 32 people died.

Volcanic eruption at Eyjafjallajökull, Iceland, 2010


Iceland is a volcanic island in the North Atlantic Ocean directly above an ocean ridge (underwater mountain chains) where the North American and Eurasian tectonic plates are being pulled apart, creating a constructive plate margin. The geological history of Iceland began in the Tertiary Period some 20 million years ago making it one of Earth’s youngest landmasses. Beneath Iceland, a column of super-heated rock called a mantle plume causes hot rock to rise, this is known as a hotspot and is the reason why Iceland grew taller than other parts of the ridge. As the plates are pulled apart by about 2-3cm a year, the pressure is reduced and the hot rock melts and erupts as lava. Repeated eruptions are how Iceland is believed to have been created. Today, Iceland continues to grow and is the second largest island in Europe, after the UK. There are over 30 active volcanoes in Iceland.


In March 2010, one of these volcanoes, Eyjafjallajökull (hay-yah-feeah-tlah-eeaah-kuh-tl) erupted. The name comes from three Icelandic words ‘eyja’ which means island, ‘fjall’ which means mountain, and ‘jökull’ which means glacier. At first, the eruption consisted of basaltic lava flows and many tourists, people who visit a place away from their home for more than 24hours went to see it. Typically, basaltic lava flows do not produce towering ash clouds. However, the volcano’s crater lies beneath a glacier, a slow-moving river of ice. During eruptions, the ice melts and glacial meltwater floods into the volcano’s vent where it meets the magma. The sudden cooling causes the magma to produce ash. Consequently, Eyjafjallajökull is built up of layers of lava and ash making it one of few composite, or stratovolcanoes in Iceland. Most of Iceland’s volcanoes are shield volcanoes.


The primary effects included:

  • Agricultural land was destroyed by ash.
  • The ash cloud of over 10km brought European airspace to a halt – planes were grounded. Airlines lost around £130 million per day.


The secondary effects included:

  • Glacier meltwater triggered floods that closed roads.
  • Travel companies such as TUI started losing between £5 million and £6 million per day.
  • Other transport companies such as cruise ships and the Eurostar benefitted as travellers looked for alternative ways of travelling.
  • Sporting events were cancelled.
  • Fresh food and flower imports stopped.


The immediate responses included:

  • The then Prime Minister, Gordon Brown announced a financial support package for airlines.
  • 800 people living nearby were evacuated. Most of those evacuated were local farmers.
  • A construction crew working on a nearby harbour were instructed to dig holes around Highway 1 to divert water that threatened a newly built bridge.

The long-term responses included:

  • Countries like the UK announced financial support packages for airlines that had been affected.


A protective wall prevented Highway 1, a ring road around the island from flooding. Residents had already made-up emergency evacuation bags due to increased earthquake activity before the eruption.

Volcanoes and climate


Like Earth’s continents, the climate is not ‘fixed’, it experiences change. We know that volcanoes can have an impact on climate. During the Archean Eon which lasted between 4 and 2.5 billion years ago, Earth was dominated by submarine volcanoes (underwater volcanoes). These volcanoes erupted large quantities of greenhouse gases such as methane and carbon dioxide into Earth’s early atmosphere – this process is known as volcanic degassing. Water vapour was also emitted alongside methane and carbon dioxide. When Earth began to cool (after accretion stopped), the water vapour condensed forming clouds that rained down to give us the oceans. Our knowledge from zircons (small grains within rocks) tells us that the oceans were probably here by 4 billion years ago – they would have been very acidic.


During the Hadean and Archean Eons, the Sun was not as bright as it is today – Earth should have frozen over, but it did not. The greenhouse gases that erupted from volcanoes trapped the Sun’s heat energy in the early atmosphere which kept Earth warm enough to sustain life. As a result, stromatolites started forming on our ocean floors some 3.8 billion years ago. The stromatolites absorbed carbon dioxide during photosynthesis and produced oxygen as a by-product. This oxygen built up in the atmosphere. So, in this way volcanoes were responsible for global warming and regulating Earth’s climate during the Precambrian Eons and you could argue that their role in producing our atmosphere nudged biological evolution along. Nowadays, volcanoes can affect local weather and mostly have a cooling effect on Earth’s climate.


Locally, volcanoes make their own weather. Water vapour released from the magma into the air is carried high into the atmosphere in eruption columns where it cools and condenses. The water droplets coalesce into clouds that produce heavy rains. This can cause lahars that can have a devastating impact on villages and towns close to volcanoes.


The greatest volcanic eruption since humans have evolved in the past 2.6 million years, was the eruption at Lake Toba in Sumatra, Indonesia, about 74,000 years ago. The eruption sent 670 cubic miles of ash into the atmosphere. Most ash falls out of the atmosphere within rain a few hours or days after the eruption, but winds can pick up smaller particles that remain causing the ash to travel far distances, often worldwide. The amount of ash from Toba would have blocked out the Sun’s rays and caused total darkness across the region for several weeks – this would have created a regional drop in temperatures. As well as ash, volcanoes can erupt large quantities of sulphur dioxide which is much more effective than ash particles on cooling the climate. Toba erupted 100 times more sulphur dioxide than Mount Pinatubo did in 1991 (and that caused a global drop in temperature of 0.5°C). Lake Toba’s eruption caused a global cooling of 3-5°C. The sulphur dioxide is sent high into the stratosphere, above the clouds and so is not washed away by rain. Instead, it reacts with water vapour and creates a volcanic aerosol that reflects the Sun’s energy back into space, preventing it from reaching the Earth’s surface. Consequently, global temperatures drop.

Living near a volcano


Volcanoes are powerful forces that can have a significant impact on people, property, and the economy. We know where volcanoes are located and how they form, and we know the potential hazards associated with volcanoes. From previous events like the eruptions from Mount Nyiragongo and Eyjafjallajökull, it is obvious that living near volcanoes can come at a cost. However, despite previous events and our knowledge of volcanoes, over 29 million people worldwide live within 10km of an active volcano and over 800 million people live within 100km of an active volcano. There are several reasons for this.


Some people have no choice. A person living in Indonesia, the Philippines or Japan is likely to live in a home no more than 100km away from an active or dormant volcano. People living on the western side of the Americas, in most of the Caribbean, in a belt from southern Italy to eastern Turkey, on the North Island of New Zealand, and around the south-west Pacific face similar issues. In these countries, the infrastructural investment in cities is so great that it is simply not economically viable to abandon them on the probability that a volcano ‘might’ erupt.


Some people do have a choice and choose to live near volcanoes for agricultural purposes. When a volcano erupts, the ash lands on nearby farmland and smoothers crops. In the short term, this can lead to crop failure and issues with food supply. On the other hand, in the long term, the ash clouds formed by volcanoes settles on the land. Over time, the ash undergoes physical and chemical changes, turning it into andisols (volcanic soils) that are rich in minerals such as iron, phosphorous and potassium. The soil is very fertile and perfect for growing crops. In 2002, during the eruption of Mount Nyiragongo, many farmers fled their fields. Those farmers started returning in 2016 to find increased harvests from the rich volcanic soil.


Another reason for living near a volcano is because of potential employment in mining. When a volcano erupts, minerals are brought to the surface. In Indonesia, there are many men working as sulphur miners. Each day, the miners collect yellow lumps of hardened sulphur, known locally as ‘devil’s gold’. The sulphur is used to bleach sugar, make matches and fertiliser, and harden rubber in factories. It is a dangerous job that can result in poisoned lungs and skin covered in scars and burns. Many people have died doing it. In other parts of the world, people mine gold, copper, iron, and diamonds.


Volcanoes attract tourists. Volcanoes are generally beautiful to look at, and they can be found in picturesque parts of the world. An erupting volcano is a spectacular sight and exciting to watch. Locals can earn money providing accommodation and services to tourists who enjoy sightseeing, hiking, or are part of an educational tour. For Iceland, tourism is the country’s main source of income. However, Iceland are struggling to meet the needs of tourists and with the rise of Airbnb, more homes are being used for tourists which has resulted in rising house prices. Italy is another example of a country that benefits from tourism. People come from all over to climb to the summit of Vesuvius, or observe Mount Etna, one of the world’s most active volcanoes. Other tourists may visit the excavated remains of Pompei.


Finally, volcanoes can be used to supply power. The hot molten rock heats water below the surface. This hot water is extracted and cools when it reaches the surface. The sudden cooling of the hot water causes evaporation and produces steam. The steam spins a turbine that turns a generator and produces electricity. The electricity is then exported to the national grid, and the steam condenses to form water again. The water is then injected back into the ground. Geothermal energy in Iceland currently generates 25% of the country’s electricity. The Philippines, Indonesia and New Zealand are big users too. Alternatively, the steam that is produced when the hot water cools upon reaching the surface can be piped and used as a direct source of heat. That is how Reykjavik, the capital of Iceland meets its heating needs. However, the extraction of water can lead to ground subsidence which can increase flood risk, affect food supply, and cause towns and cities to sink.

Reducing the risks from volcanoes


Like earthquakes, volcanic eruptions and their associated hazards are natural events. Volcanic eruptions only become a hazard when they pose a risk to people and property. Again, similar to earthquakes, we can reduce the effects of volcanic eruptions through monitoring, prediction, protection, and planning. Volcanoes usually give advance warning signals before an eruption and it is crucial to look of for them. State-funded observatories use a range of equipment to monitor volcanic activity.


An increase in earthquake activity around volcanoes is not to be ignored. Before a volcano erupts, the movement of magma through the lithosphere exerts (applies) a lot of force on the rocks around it. This can cause those rocks to fracture resulting in low magnitude earthquakes. The earthquakes are recorded using seismometers.


Volcanoes change shape when magma is accumulating, before an eruption or withdrawing, after an eruption – this is known as ground deformation. When a volcano or a feature such as a lava dome swells, it is said to be inflating, and when the surface subsides, it is said to be deflating. Out of the two, inflation is the more obvious sign of a possible eruption. Satellites and tiltmeters are used to monitor ground deformation. However, the most active volcanoes undergo non-eruptive cycles of inflation and deflation, so ground deformation is not the most telling sign of an impending eruption, unless supported by other data.


Volcanoes erupt gases. An increase in sulphur dioxide output from a volcano provides a good indication that gas-rich magma is moving closer to the crater. However, the corrosive nature of sulphur-rich gases makes it hard to install permanent equipment that will operate for a long time. A more advanced way of detecting gases near a volcano is by satellite, but this is expensive technology and not all observatories will have access to them. As a result, volcanologists often have to collect samples themselves.


With 24/7 monitoring in place, it is possible to predict a volcanic eruption. Although, it is difficult to predict the exact day and time. The sheer power of volcanic eruptions makes it difficult to protect people and property. Buildings cannot be constructed to withstand lava flows, lahars, or the weight of ash (especially when wet) falling on roofs. Moreover, it is not possible to divert landslides, volcanic bombs, or gases away from towns. There have been attempts divert or stop lava flows. People have tried digging channels for the lava to flow into, but the lava tends to fill the channel and then continuing flowing over it. Barriers can be built to stop the lava reaching residential or tourist areas, but it is likely that the lava will overrun those barriers. Another method is to spray sea water on to the lava, but this requires lots of water canons and can take a very long time before it has an impact.


The best way to protect people and property from volcanic hazards is to plan for them. Several strategies can be used to plan for a volcanic eruption:

  • Establishing and sign-posting safe evacuation routes.
  • Designating public buildings such as schools, churches, and community centres as emergency shelter.
  • Teaching people about volcanoes so that they know what to do during an eruption.
  • Creating hazard maps that prevent building in high-risk areas where lava might flow.
  • Setting exclusion zones so that no one is allowed to go where they would be considered at risk.



Previously, we have looked at shield volcanoes; composite, or stratovolcanoes; and hotspots. Some volcanoes are more powerful than others and are capable or releasing large amounts of material such as lava and ash over huge distances. The amount of material released by a volcano determines how explosive the eruption was and is measured using the Volcanic Explosivity Index (VEI).


The VEI of Mount Pinatubo in 1991 was 6 – it released enough material to have an impact on the global climate. The VEI of Mount Nyiragongo in 2002 was 1 – it did not release much material, but the lava, ash, and gases that it did release had devastating impacts. The VEI of Eyjafjallajökull in 2010 was 4 – it released enough ash to disrupt European air travel. In 2018, the Vulcan de Feugo eruption had a VEI of 3. A volcano that spews out more than 240 cubic miles of material has a VEI of 8. That amount of ash would bury Greater London to a depth of half a mile. These eruptions are known as super eruptions and they can have global impacts. The eruption from Lake Toba 74,000 years ago is one example.


Supervolcanoes, like Toba are capable of releasing more than 240 cubic miles of lava and ash across huge distances. Toba released 670 cubic miles of material that took six years to settle. The ash and sulphur also caused global cooling, with temperatures dropping by 3-5°C. Supervolcanoes do not form typical volcanic cones. Supervolcanoes occur at hot spots or subduction zones above a mantle plume, an area in the mantle layer where hot rock rises faster than the surrounding rock. The rock melts and turns into magma. Yellowstone National Park in the USA is an example of a supervolcano that has formed at a hot spot, and Toba is an example of a supervolcano that has formed at a subduction zone.


Over time, magma accumulates in a magma chamber beneath the Earth’s crust. Heat and gases build up and apply pressure to the crust causing it to swell upwards. Just like lava domes, supervolcanoes can inflate and deflate, so the swelling of the ground does not necessarily result in an eruption. However, it is the building of pressure that eventually causes the magma to burst through the Earth’s crust resulting in a super eruption. Once the magma chamber is empty, it may collapse to form a wide depression, or crater known as a caldera. Depression comes from the Latin word ‘deprimere’, which means press down, and caldera comes from the Latin word ‘caldaria’, which means boiling pot. A new magma chamber may form beneath the caldera, leading to another enormous eruption.


Yellowstone is one of the world’s most active supervolcanoes and has experienced VEI 8 eruptions 2.1 million, 1.2 million, and 640,000 years ago. Highly volcanic regions, like Yellostone have geothermal systems of hot springs and geysers. These occur when groundwater seeps downwards through the rock. The further the groundwater goes, the closer it gets to heat from hot rock below. The heat raises the temperature of the water and the water rises to the surface and forms a hot spring. Hot springs can be used for swimming, bathing, or to produce heating. In some places, the hot water is held under pressure until it explodes out of the ground as a tall column of water and steam known as a geyser. Geyser comes from the Icelandic word ‘Geysir’, which mean to gush. Every year, thousands of tourists visit Yellowstone to experience the hot springs and see the geysers.


If another super eruption were to occur at Yellowstone, its effects would be global. There would be a blast radius of over 620 miles. About 90% of people living in the blast radius would be killed from pyroclastic events. Ash would cover the United States and spread to Europe within three days of the eruption. The sulphur dioxide released could cause a 10°C drop in global temperature for 6 to 10 years. However, a super eruption from Yellowstone is highly unlikely in our lifetime.