Why do volcanoes erupt?

How a volcano erupts

Volcanoes erupt because hot molten rock, called magma, builds up deep inside the Earth. The Earth’s interior is very hot, and this heat melts rocks under the surface.

As magma heats up, it becomes lighter and starts to rise. At the same time, gas pressure inside the magma increases.

The pressure pushes the magma upward through cracks in the Earth’s crust.

When the pressure becomes too strong, the magma breaks through the surface. This causes a volcanic eruption. Lava, ash, and gases are released into the air.

After the eruption, the pressure decreases, and the volcano becomes quiet again — sometimes for many years.