What causes volcanoes?
Inside the earth's core there is a red-hot liquid rock, called magma.

Volcanoes happen when magma rises to the surface of 
the earth, which causes bubbles of gas to appear in it.

This gas can cause pressure to build up in the mountain, 
and it eventually explodes. 
When the magma bursts out of the earth, it is called lava.

Are there different types of volcanoes?
The type of magma in the earth can create different volcanoes.

If the magma is quite thin, the gas can escape 
easily and there will not be an explosion. 
The magma just comes out of the mountain 
and flows down the sides, like Volcanoes 
in Hawaii and Mount Etna.

But, if the magma is thick and sticky, the gas cannot 
escape, so it builds up and up until it explodes.
This can cause landslides and sends out huge 
clouds of burning rock and gas, which devastate 
everything around them, like the famous eruptions 
at Mount St Helens and Montserrat.

What effects do volcanoes have?
----Volcanoes can change the weather
They can cause rain, thunder and lightning. 
Volcanoes can also have long-term effects 
on the climate, making the world cooler.

----Fast-moving lava can kill people and falling 
ash can make it hard for them to breathe. 
They can also die from famine, fires and 
earthquakes which can be related to volcanoes. 
People can lose their possessions as volcanoes 
can destroy houses, roads and fields.

-----Lava can kill plants and animals too. 
The Mount St Helens volcano in 1980 killed an estimated 
24,000 animals including 11,000 hares, 6,000 deer, 
300 bobcats, 200 black bears and 15 mountain lions.

Can we predict when a volcano is going to erupt?
Scientists who specialise in volcanoes are called volcanologists.

They are getting better at predicting volcanoes. 
The most reliable method is listening to 
the 'rumbles' inside a grumbling mountain.

They also look at the changes in the gases 
which come out of volcanic mountains, the angle of the 
slopes, and bizarrely, the behaviour of animals in the area.

Animals often seem to be able to 'detect' when an eruption 
is coming, and they become agitated and worried.

Which volcano has killed the most people?
The volcano eruption in Tambora, Indonesia, 
in 1815, killed around 92,000 people.

The eruption sent fiery ash into the stratosphere, 
which cooled the world climate for more than a year.

In some parts of the world, that year is called 'the year 
without a summer' because it was so cool. 

Tambora also destroyed crops, and led 
to disease and water contamination.

Do volcanoes do anything good?
Volcanic ash is very good for soil, so plants 
grow quickly and strong after a volcano.

Volcanic slopes left after an eruption are very 
steep, so rare and delicate plants and animals 
can set up home there and be protected.

Volcano facts
----One in 10 people in the world live within 'danger range' of an active volcano.

----There are around 1510 'active' volcanoes in the world. 
Volcanologists disagree on what comes under the term 'active', 
but 1510 volcanoes have erupted in the last 10,000 years, 
which means they are active in the world of volcanoes. 
There are thought to be many more volcanoes on the sea bed.

----The biggest volcano in the world is Mauna Loa in Hawaii. 
Its whole volume is about 80,000 cubic kilometres.

----Sometimes lightning is seen in volcanic clouds. 
It's not clear why this happens but it could be 
to do with lots of hot particles bashing into 
each other, causing static charges.

previous         main page