What is a volcano?

A volcano is a very deep hole in the Earth’s top layer that can let out hot gasses, ash and lava. Many volcanoes are also mountains.

Volcanoes have long shafts that go all the way down through the Earth’s first layer, the crust, to magma in between the crust and the mantle (the Earth’s second layer). It’s so hot there that rocks melt into liquid! This is called magma, which travels up through volcanoes and flows out as lava.

Top 10 facts

  1. Volcanoes are big holes that let out hot gasses, ash and magma from deep inside the Earth.
  2. Many volcanoes are mountains, made up of layers of lava and ash.
  3. Many volcanoes have several vents – a main one, and secondary ones that branch off the main vent. The volcano’s main vent goes all the way down to the layer of magma in between the Earth’s crust and mantle.
  4. The Earth has three layers – the crust at the very top, then the mantle, then the core at the very middle of the planet.
  5. There are three ways to describe a volcano and explain what it’s doing  – active, erupting, and dormant.
  6. An extinct volcano is one that hasn’t erupted in at least 10,000 years, and that scientists don’t think will erupt again for a very long time.
  7. The largest active volcano in the world is Mauna Loa, on the Hawaiian islands.
  8. When a volcano erupts, magma comes up and out through the vents. Magma is called lava when it’s outside the volcano.
  9. Depending on how thick the magma is, volcanoes can be different shapes such as shield, composite or dome.
  10. Ash from volcanoes is very good for growing things. It adds nutrients to the soil.

Did you know?

  • The Earth has three layers:
    • crust (at the top)
    • mantle (in the middle)
    • core (in the centre)
  • There are 1,500 active volcanoes in the world.
  • About 50 volcanoes erupt every year!
  • The largest active volcano is Mauna Loa.
  • Most volcanoes can be found in countries that have coastlines on the Pacific Ocean – this is called the Ring of Fire.
  • Gas, ash and magma can come out of volcanoes.
  • When magma flows out of a volcano, it’s called lava.
  • Most of the gas that comes out of volcanoes is poisonous.
  • Some volcanoes are underwater!
  • There aren’t any volcanoes in the UK.
  • The largest volcano in Europe is Mount Etna in Sicily.
  • The word ‘volcano’ comes from ‘Vulcan’, the Roman god of fire

Volcano pictures

Have a look through the images in the gallery and see if you can spot the following:

  • Layers of the Earth
  • The parts of a volcano © Anthony Bennett, Internet Geography
  • Mauna Loa erupting
  • Map of the Ring of Fire, and major volcanoes
  • Diagram of a shield volcano
  • Diagram of a composite volcano
  • Diagram of a dome volcano
  • Mount St Helens (dome)
  • Mt Cotopaxi (composite)
  • Mauna Kea (shield)



Magma is liquid rock in between the crust and the mantle, formed when part of the lower crust or upper mantle melts.

When magma travels up through a volcano’s vent, bubbles of gas also appear. All the gas builds up pressure, which causes the magma to explode out of the volcano. When magma is thin, the gas bubbles can rise and pop easily – volcanoes located over thin magma don’t have very large explosions. When magma is thick, the gas bubbles get trapped and the pressure builds up so much that the explosion shoots high up into the air. If magma cools down as it rushes up the vent, it will come out as rock or ash.

Volcanoes can be very dangerous. Lava flowing out of volcanoes can burn and destroy anything in its path, and ash can be so thick in the air that it’s hard to breathe. Earthquakes can happen when a volcano erupts, causing very large waves called tsunamis. If gasses and ash get into the atmosphere, it can even change the weather by causing thunderstorms and cool temperatures.

Volcanologists (scientists who study volcanoes) can sometimes tell if a volcano is going to erupt by keeping track of earthquakes underneath it. The types of gasses coming out of the vent can also change close to an eruption. Animals living near a volcano may start to act differently, as if they can sense something is going to happen.

The Earth’s surface is made up of lots of pieces called tectonic plates. These plates can slide against each other, which lets magma from underneath squeeze up through the cracks. When tectonic plates move, it also causes earthquakes. Most volcanoes are located along the edges of tectonic plates, especially around the Pacific Ocean – this is called the Pacific Ring of Fire.

The ancient Romans wrote about a huge volcanic eruption that happened in 79 AD in Pompeii. The ash and rocks that erupted out of Mount Vesuvius buried nearby towns and killed more than 1,000 people. Mount Vesuvius is dormant today.

Other famous volcanic eruptions in history are:

  • Mount Tambora (Indonesia) in 1815
  • Krakatoa (Indonesia) in 1883
  • Mount Pelée (Martinique) in 1902
  • Mount St Helens (Washington, USA) in 1980
  • Mount Pinatubo (Philippines) in 1991
  • Eyjafjallajokull (Iceland) in 2010

Words to know

  • Active volcano – a volcano that erupts regularly
  • Crater – the bowl-shaped area at the top of a volcano’s vent
  • Dormant volcano – a volcano that has not erupted in a very long time, but could again
  • Extinct volcano – a volcano that has not erupted in thousands of years, and doesn’t look like it will erupt again
  • Magma chamber – the pool of magma located underneath the volcano’s vent
  • Supervolcano – a volcano that has an eruption where the amount of stuff that comes out is more than 1,000 cubic kilometres
  • Vent – the main part of a volcano where magma and gasses come through from deep inside the Earth
  • Volcanologist – a scientist who studies volcanoes

Related Videos

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Children's books about volcanoes


See for yourself

  • Visit the Natural History Museum: their brand-new gallery about volcanoes and earthquakes features an earthquake simulator where you can feel the groud shake underneath your feet, as well as a heat suit worn by volcanologists.
  • Watch an animation of a volcano erupting from the safety of your own home!

Find out more

A Comparison of Volcanic Eruptions

Also see