<P> A magma chamber is a large pool of liquid rock beneath the surface of the Earth . The molten rock, or magma, in such a chamber is under great pressure, and, given enough time, that pressure can gradually fracture the rock around it, creating a way for the magma to move upward . If it finds its way to the surface, then the result will be a volcanic eruption; consequently, many volcanoes are situated over magma chambers . These chambers are hard to detect deep within the Earth, and therefore most of those known are close to the surface, commonly between 1 km and 10 km down . </P> <P> Magma rises through cracks from beneath and across the crust because it is less dense than the surrounding rock . When the magma cannot find a path upwards it pools into a magma chamber . These chambers are commonly built up over time, by successive horizontal or vertical magma injections . Influx of new magma causes reaction of pre-existing crystals and the pressure in the chamber to increase . </P>

Where is the lava stored in a volcano