Bishara and Son Dear Bishara and Son, The Earth has volcanoes because it is hot inside. In some places it is hot enough to turn solid rock into liquid rock. Geologists call the liquid rock magma. If the magma reaches the surface it is called lava and lava accumulates to make a volcano.
Volcanoes grow by intrusion and extrusion.
This way the volcano grows on the inside. An extrusion is an eruption. It can add layers of lava or ash. This way the vo lcano grows on the outside. Volcanoes erupt because of density and pressure.