Caldera

A large, usually circular depression at the summit of a volcano, formed when magma is erupted from a shallow underground magma reservoir. The removal of large volumes of magma may result in loss of structural support for the overlying rock, thereby leading to collapse of the ground and formation of a large depression (called a collapsed caldera). Calderas are different from craters, which are smaller circular depressions created primarily by explosive excavation of rock during eruptions.