How do volcanoes erupt for kids

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Why do volcanoes erupt? - Nicholas, age 3 years and 11 months, Northmead, NSW.

The rock inside the planet we live on can melt to form molten rock called magma. This magma is lighter than the rocks around it and so it rises upwards. Where the magma eventually reaches the surface we get an eruption and volcanoes form.

The top part of the Earth is made up of a number of hard pieces called tectonic plates. Magma and volcanoes often form where the plates are pulled apart or pushed together but we also find some volcanoes in the middle of tectonic plates.

Read more: Curious Kids: why doesn't lava melt the side of the volcano?

Volcanoes have many different shapes and sizes, some look like steep mountains (stratovolcanoes), others look like bumps (shield volcanoes) and some are flat with a hole (a crater or caldera) in the centre that is often filled with water.

The shape of the volcano and how explosively it erupts depend largely on how “sticky” and how “fizzy” (how much gas) the magma is that is erupted.

For example, if you try to blow bubbles in cooking oil though a straw, the bubbles can escape quite easily because the cooking oil is runny.

If you try to blow bubbles in jam or peanut butter you would find it very difficult because the jam and peanut butter are very sticky, they wouldn’t move much at all if you tried to pour them out of the jar.

It is the same with volcanoes. When magma rises towards the surface gas bubbles start to form. Whether or not they can escape as the magma is rising affects how explosive the eruption will be.

Where the magma is runny like cooking oil and doesn’t have much bubbly gas mixed in it, such as places like Hawaii, then we see lots of slow-moving lava flows and shield volcanoes. Lava is what we call magma when it reaches the surface.

Here are some pictures of a recent Hawaiian eruption:

However, where the magma is very sticky, like jam or peanut butter, and if it contains a lot of bubbly gas then the gas can get stuck and eruptions can be very powerful and explosive, like the recent eruptions at Fuego volcano in Guatemala.

Damage caused by eruptions

In explosive eruptions the frothy, bubbly magma can be ripped apart into tiny bits called volcanic ash. This is not ash like you get after a barbecue or fire, it does not crumble away in your fingers. It is very sharp and is dangerous to breathe in.

Some explosive volcanoes can send ash high up into the sky and it can travel around the world over different countries. If aeroplanes travel through an ash cloud from a volcano it can cause a lot of damage to the engine.

Other explosive eruptions create fast-moving, hot clouds of volcanic ash, gas and rocks that travel down the sides of the volcanoes and destroy pretty much everything in their path.

The benefits of volcanoes

Despite the great damage they can cause, volcanoes also help us to live. Volcanic ash provides food for the soil around volcanoes which helps us grow plants to eat. The heat from some volcanoes is used to make energy to power lights, fridges, televisions and computers in people’s houses.

You can find some more information about different types of volcanoes here and here.

Read more: Curious Kids: Do most volcanologists die from getting too close to volcanoes?

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The word volcano comes from the name of Vulcan, the ancient Roman god of fire and metalworking. The Romans believed that volcanic eruptions resulted when Vulcan made thunderbolts and weapons for the gods. Other cultures explained volcanoes as outbursts of anger from a god or goddess. Pele was the name of the volcano goddess of the native Hawaiians.

Volcanoes have a long history of destruction. In ad 79 the eruption of Mount Vesuvius destroyed the Roman cities of Pompeii and Herculaneum.

Two of the deadliest volcanic eruptions happened in 1815 and 1883 on islands in what is now Indonesia. In 1815 Mount Tambora released so much ash into the air that it blocked out large amounts of sunlight. Temperatures around the world dropped for months afterward, making 1816 a “year without a summer.” In 1883 the volcano Krakatoa exploded and collapsed, triggering a colossal sea wave known as a tsunami. Tens of thousands of people were killed by these events.

On May 8, 1902, Mount Pelée erupted on the Caribbean island of Martinique. Although very little lava flowed, an unstoppable black cloud of hot gases and ash engulfed the city of Saint-Pierre, killing almost all of its 30,000 people. The birth of a volcano was witnessed between 1943 and 1952, when a smoking hole in a Mexican farmer’s cornfield erupted into a new mountain called Paricutín that eventually stood 1,400 feet (425 meters) above the level ground around it.

Another notable event took place in 1963, when a new volcanic island called Surtsey rose up from the Atlantic Ocean near Iceland. Within a few years it built up to an area of 1 square mile (2.5 square kilometers), with a peak more than 560 feet (170 meters) above sea level.

The 1980 eruption of Mount Saint Helens, in the U.S. state of Washington, was one of the biggest in North America. The 1991 eruption of Mount Pinatubo, in the Philippines, was the largest of the 1900s. These eruptions killed fewer people than earlier volcanoes, but they still destroyed much property.

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