Deep inside the Earth, it is very, very hot. Because of this heat, rocks melt and turn into a thick, hot liquid called magma.
Magma also has gases trapped inside it, just like bubbles in a fizzy drink.
Over time, the magma and gas start to build up pressure under the ground. There isn’t much space, so the pressure keeps getting stronger and stronger.
Finally, the pressure becomes too strong to stay inside.
Boom! The volcano erupts!
The magma pushes its way up through a hole in the Earth and comes out as lava, along with gas, ash, and smoke.