Volcanoes

FAQs

What is a volcano?

A volcano is an opening in the Earth’s crust through which molten rock (magma), gas and ash erupt, often with powerful force.

The word ‘volcano’ can be used to describe the opening itself or the cone-shaped mountain that is built up around it.

What happens when a volcano erupts?

Volcanic eruptions are caused by the growing pressure of gas that has built up in the magma. When the pressure becomes too great the magma is forced onto the Earth’s surface, where it is known as lava.

Some magma cools and solidifies on its way upwards and may be blasted out as enormous chunks of hot rock, or as volcanic ash and dust.

Currents of very hot gas and rock particles, called pyroclastic flows, may sweep over the landscape at high speed destroying everything in their path. Dust can remain in the atmosphere for years and cause vivid sunsets all over the world.

Are all volcanoes the same?

No, there are different types of volcanoes. The nature of a volcano depends on how viscous, or sticky, the magma is. This depends on its temperature and the amount of silica (a mineral) it contains.

If the silica content is low, the lava flows out gently, forming a shallow shield-shaped cone. Lava with a very high silica content erupts slowly to form a dome, usually within an existing crater.

Composite volcanoes cause the most dangerous, highly explosive, eruptions. These are volcanoes with alternate layers of rock and lava. The magma is moderately viscous and it is mixed with other materials.

Where do volcanoes occur?

The Earth’s surface is divided into several plates, known as tectonic plates, which are moving all the time. Most of the Earth’s active volcanoes are located along the edges of tectonic plates.

Are all volcanoes dangerous?

Potentially, yes. Volcanoes can be divided up into 3 categories depending when they last erupted: active, dormant and extinct.

An active volcano has erupted in the last 10,000 years. Between eruptions it may be dormant and if it hasn’t erupted in 10,000 years it is considered extinct. However, it is impossible to tell whether a dormant volcano will ever erupt again so it is hard to be sure which volcanoes are truly extinct.

Eruptions from volcanoes that have been inactive for a long time tend to be particularly violent.

Can we predict when a volcano is going to erupt?

Scientists who study volcanoes, vulcanologists, look at several factors to help them predict eruptions.

They measure the frequency of earthquakes under the volcano and changes in the angle of the volcano’s slope. They also study the gases that are sometimes given off by volcanoes in small quantities between eruptions.

This helps them to predict an eruption so that people can be evacuated from the local area if necessary. However, it is still not possible to predict the size of an eruption accurately.

Do volcanic eruptions happen in Britain?

They used to. The British landscape is full of evidence of volcanic activity, particularly the mountains of Scotland and North Wales.

However, Britain is now far from the margins of the plates that form the earth’s crust, where volcanic activity is most frequent, so the probability of a volcanic eruption in the UK is now very low.

Are there volcanoes on other planets?

Yes, plenty, but most volcanoes in our solar system seem to be inactive. There are exceptions though. The innermost of Jupiter's moons, Io, has active volcanoes. In fact, it is the most volcanically active body in the solar system, so far as we know.

The volcanoes on Venus and Mars are far larger than on Earth. On Mars, the 16 mile high Olympus Mons is the largest known volcano in our solar system.

Supervolcanoes

Museum scientist Camilla Wilkinson (based at The Open University, Buckinghamshire) researches supervolcanic eruptions. A supervolcano is a volcano that ejects material greater than 1,000 cubic km, which is significantly bigger than any volcanic event in recent history.

Supervolcanic eruptions are not common, but they can have devastating effects, because they usually cover huge areas with lava and ash. 

Effects of an eruption

This can cause long-lasting climate change which can even bring species to extinction. One of these climate changes is known as a ‘volcanic winter’ or mini ice age, which is caused by the ash blocking the sunlight from reaching the Earth’s surface. 

Also, the large quantities of gas that are released, for instance sulphur, cause reactions in the atmosphere that create acid rain.

Dating eruptions

When an explosive volcanic eruption occurs, the air is filled with ash. This ash then becomes consolidated along with lava to form thin or thick layers of a rock called ‘Tuff’. Camilla is researching a technique (Ar-Ar geochronology) to define the age of these rocks in order to precisely date when the eruptions took place.

Camilla’s recent research involves investigating ways of making this dating technique more precise and she will be studying and dating rocks from Yellowstone National Park, USA. 

The eruption cycle in Yellowstone National Park

Three super eruptions have occurred at Yellowstone in the past 2.1 million years and according to scientists its eruption cycle is approximately every 600,000. The last eruption occurred around 640,000 years ago, so being able to predict when the next eruption could happen is very important.

Although her research is not about making predictions, it will advance our understanding of volcanic systems and allow us to look at the possible outcome if a super volcanic eruption occurred today.

Environmental impact

Volcanoes can be very destructive and can have a devastating effect on the environment. Their ground shaking explosions, suffocating toxic gases and lava flows can have a serious impact on both a local and global scale, but the type of devastation depends on the type of volcanic activity.

Immediate impacts

Different type of eruptions will have different effects on the environment. For example, slow lava flows range from 700°C to 1300°C, so they burn everything they touch. They can also generate enough heat to burn people standing near the flowing lava.

A pyroclastic flow (which is a fast explosion of gases, rocks and ash) can travel as fast as 700km/h and is much deadlier than the other types of eruptions. The gases are poisonous and produce heat over 1000°C that can kill the vegetation. Also, the rocks from the explosion can flatten trees and buildings, and everything gets covered in ash.

Impacts on the atmosphere

Volcanic gas is an important agent of global climate change. It is usually a mix of water, carbon and sulphur dioxide, but can also contain carbon monoxide and other poisonous chemicals.

An eruption emits tonnes of ‘aerosol gases’ into the air, which with wind currents can cause an impact all over the world. Sulphur dioxides can cause acid rain and even cool the Earth’s temperature by 1°C, which can make a huge difference on annual crop growth. All these gases also increase ozone layer destruction.

Impacts on the vegetation

Heat and poisonous chemical components from the gases cause surrounding plants and trees to wilt and ultimately be destroyed. This happens either because of immediate strong contact with gases or long term exposure. The lava can burn the vegetation and might leave the land barren.

There is so much pressure building up beneath the Earth’s surface, that when an explosive eruption takes place the material released can be strong enough to flatten trees.

Impacts on the soil

Volcanic soil is fertile. In the Canary Islands, for example, grape vines are grown on volcano slopes.

Although vegetation dies during a volcanic explosion, the plants and trees can recover quite quickly afterwards, if the poisonous gases are not too strong.

On a larger scale, volcanic eruptions also change the morphology of the surrounding landscape. This can have an impact on water tables, and river courses, leading to flooding.

A case study: the Mount Pinatubo volcanic eruption (Philippines)

The Mount Pinatubo volcano erupted in 1991, after over 500 years of dormancy, producing the second largest eruption of the 20th century. Much of the area surrounding the volcano, including thousands of houses, was destroyed by volcanic deposits (ash and mudflows). The ash cloud (containing 5 billion cubic metres of ash) covered an area of over 125,000 km², bringing total darkness to cities nearby.

Thankfully, the Philippine Institute of Volcanology and Seismology issued a warning and many people were evacuated, limiting the number of deaths to 847. The main cause of death was roofs collapsing under the weight of accumulated wet ash. All the growing crops were covered in ash, and much of the livestock was also killed.