Why do volcanoes erupt?

Answer by  crabbiehoneybunnie (77)

When the rocks inside the earth become hot enough to melt they become less dense than the surrounding solid rock. The low density of the magma will cause it to rise to the surface of the Earth. Only if the magma contains water or dissolved gasses will expand in to steam and gas causing a violent eruption.

Answer by  loos (35)

Volcanoes erupt because the pressure of magma underneath the earths surface increases. And the only way to release pressure is to Go up and out. So The magma pushes through small pipes that go through the earths crust before it finally comes out at a point on the earth, called a volcano.