Volcanoes are evidence of the powerful forces at work inside the Earth.
Below the Earth's core there's a red-hot liquid rock called magma.
A volcano is a rupture on the Earth's crust, which allows lava, ash, and gases to escape, when magma rises to the surface.
The UK doesn't have any active volcanoes.
There are three common types of volcano: composite volcanoes, often the most deadly; shield volcanoes, which are large but usually less violent; and cinder cones.
Volcanoes can change the weather. They can cause rain, thunder and lightning.
They can also have long-term effects on the climate.
Fast-moving lava can kill people and falling ash can make it hard for them to breathe. Lava can also kill plants and animals too.
Scientists who specialise in volcanoes are called volcanologists. They are growing more and more confident at predicting when volcanoes will erupt in the short-term.
If a volcano was going to erupt in one hour they'd have a good idea it was going to happen. If it was going to blow in a week they'd be less sure, and in six months even less so.
The further a volcano is from erupting, the harder it is to predict. Working out if a volcano will erupt in future years is still impossible.
Volcanologists combine several techniques to predict what will happen.
They use monitors to detect movement in the rocks that make up the volcano and in the Earth's crust. They also measure the gases that come out of the volcanic mountains, and even the angle of the slopes.
If an eruption is likely to happen very soon the behaviour of animals in the area can be a clue.
Animals often seem to be able to 'detect' when an eruption is coming, and they become agitated and worried.
And volcanologists are always trying to find new ways to detect eruptions. Some are now using satellites to try to understand how and when they may blow.
Volcanic ash is very good for soil, which helps plants to grow 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.
- 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.
- Indonesia has the largest volcano chain in the world. Chile has the second largest chain, with about 500 that are potentially active.