- from Volcanoes
The roots of volcanoes lie 40 to 120 miles inside the Earth in a layer called the mantle.
Temperatures there are as hot as 4,000°F—so hot that rock can melt like a chocolate bar on a summer day. The hot, melted rock becomes a thick, flowing substance called magma. Magma is lighter than the solid rock surrounding it, and it pushes up through cracks in the Earth. Wherever magma comes out, volcanoes form and grow. Once it is out of the ground, magma is called lava. As lava cools, it hardens into different kinds of rock.