Earth, between the molten iron core and the thin crust at the surface,
there is a solid body of rock called the mantle.
When rock from the mantle melts, moves to the surface through the crust,
and releases pent-up gases, volcanoes erupt.
Extremely high temperature
and pressure cause the rock to melt and become liquid rock or magma.
When a large body of magma has formed, it rises thorugh the denser rock
layers toward Earth's surface. Magma that has reached the surface
is called lava.