Nova | Volcano's Deadly Warning | Anatomy of a Volcano: Caldera

Caldera
A caldera is a large, usually circular depression at the summit of a volcano formed when magma is withdrawn or erupted from a shallow underground magma reservoir.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. Calderas are different from craters, which are smaller, circular depressions created primarily by explosive excavation of rock during eruptions.

Left: Mount Aso vents a large cloud of steam at Japan's Aso National Park. The mountain's caldera is one of the world's largest.