Sketch of a magma reservoir and conduit beneath a volcano

Sketch by B. Myers


Magma is molten or partially molten rock beneath the Earth's surface. When magma erupts onto the surface, it is called lava. Magma typically consists of (1) a liquid portion (often referred to as the melt); (2) a solid portion made of minerals that crystallized directly from the melt; (3) solid rocks incorporated into the magma from along the conduit or reservoir, called xenoliths or inclusions; and (4) dissolved gases.

This sketch shows a classic cartoon view of a magma reservoir beneath a volcano and a conduit leading up to a lava dome at the surface. The arrow indicates direction of magma movement from a deeper source.