A volcano is made up of many, many layers of rock. The top layers of solid rock lay on the Earth's crust. As you go down toward the center of the Earth, the rock gets hot and then melts. The melted rock is called magma. Volcanoes are formed by holes that get poked in the Earth's crust. Magma makes its way up to the holes and then the volcano erupts. When magma reaches the surface of the Earth it turns to lava. When lava cools it hardens to form igneous rock.