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depression at the summit of a volcano formed when magma is withdrawn or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. Craters are smaller, circular depressions created primarily by explosive excavation of rock during eruptions.
Hope I helped : )
