Why do volcanoes erupt?

Volcanoes can erupt when pressure deep underground forces hot, liquid rock (called magma) from inside the Earth up to the surface. An eruption blasts out clouds of ash and molten (melted) rock into the air around it.

Stages

1. Magma rises up a main pipe from deep within the Earth’s crust and is forced toward the surface.
2. Pools of magma build up deep underground. This hot, liquid rock comes from the Earth’s interior.
3. Thick clouds of burning hot ash are blasted up to several miles into the Earth’s atmosphere.
4. At the Earth’s surface, magma is called lava, which flows down the sides of the volcano. The lava cools in layers, often with ash in between, that gives the volcano its cone shape.