How do volcanoes erupt?

Wonderful Earth and Space

Click on the links below to go to film clips and images to help you answer the questions.

Here are some of the questions you might have to think about -

  • What are the properties of the Earth?

  • What are the layers of the Earth called?

  • What causes a volcano to erupt?

  • Which are the most famous volcanoes in the world?

  • How do volcanoes impact of peoples lives?

  • Why do people choose to live near volcanoes?

  • How can we re-create an erupting volcano?

  • What causes earthquakes?

  • How do scientist measure earthquakes?

  • What are tectonic plates?

And lot's more ............

Are you ready to find some of the answers?

The layers of the Earth

First let us look at the layers of the Earth to find out more about the planet we live on.


Let's get ready to dig

The first layer is called the crust. This is the thinnest layer. The land is made of continental crust and made mostly from a rock called granite. The layer beneath the ocean bed is made of oceanic crust and is made mainly from a rock called basalt.

The next layer is called the mantle. There are two parts to the mantle. The upper parts of the mantle the rock is hard, but lower down the rock is soft and beginning to melt. This semi-molten rock is called magma. It is the widest section of the Earth. Very hot - hot enough to melt rock.

The next layer is the outer core. This is a liquid layer that is made up of iron and nickel. It is extremely hot.

The layer in the middle is the inner core. It is the hottest part of the Earth. It is solid and it is also made up of iron and nickel, 

Digging down into the Earth

Volcano Facts

What do we know about volcanoes?
Well, there all over the world; though there are no active ones in Britain – not now anyway.
Volcanoes occur in places where the plates of landform weak points. These are known as fault lines.

Types of volcano - There are many different types of volcanoes. They range from small cracks in the Earth's surface to very large mountains which have been built up by layers of lava and ash.

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

The magma travels up through a volcano's vent and as it does so bubbles of gas appear. When the magma is thin, the gas bubbles rise and pop easily on the surface. When the magma is thicker, the gas bubbles get trapped and the pressure builds up. When the pressure builds up it causes an explosion that shoots up high into the air.

If the magma cools down as it rushes up the vent, it will come out as rock or ash.

Earthquakes - These can happen when a volcano erupts, causing very large waves called tsunamis. If gases and ash get into the atmosphere, it can even change the weather by causing thunderstorms and cool temperatures.

Dormant Volcanoes - A dormant volcano is one that hasnt erupted for many years. When this happens people begin to live near the volcanoes because the land is so fertile dure to the volcanic ash. But when and if the volcano erupts again it can cause a huge loss of life. 

In the biggest explosion in recorded history, the eruption of Tambora in Indonesia in 1815, an estimated 60,000 people lost their lives and the ash cloud affected farming, causing the worst famine of the century.

The lines are around the edges of the tectonic plates. 
The Himalayas are a range of mountains that are a splendid example of two tectonic plates that crashed together pushing up the largest mountain range in the world.
When tectonic plates grind against one another, two things can result earthquakes and volcanoes. 
Volcanoes begin to form when the rocks of the lower plate get pushed deep into the Earth. There they are heated, until they melt, forming magma, a kind of liquid rock. As the magma is less dense than the rock surrounding it, it is forced upwards until it finds a weak spot in the earth’s surface and erupts out forming a volcano. 

Vesuvius is a classic example of a volcano because it is near a place where one section of the Earth's surface is being pushed down below another section. Therefore, the Earth’s surface is weak and the magma and hot ash has been forced upwards until it erupts.

Many volcanoes have not erupted for so long they are no longer considered ‘active’ (dangerous).  However, there are 1511 active volcanoes – this means they may erupt at any time.  It is guessed that 1 in 10 people in the world live within range of a dangerous volcano!

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Tectonic Plates

Cut out volcano models