A magma chamber is the chamber beneath a volcano where the magma is held before an eruption. It is the build up of pressure in this chamber that causes the eruption.

Often, a volcano may have a deep magma chamber many kilometres down, which supplies a shallower chamber near the summit. The location of magma chambers can be mapped using seismology: waves from earth tremors move more slowly through liquid rock than solid, allowing measurements to pinpoint the regions of slow movement which identify magma chambers.