Caldera
A caldera is a large volcanic depression formed when a volcano’s summit collapses inward following a major eruption or the withdrawal of magma from the chamber beneath the volcano. Unlike the relatively small crater found at a volcano’s peak, a caldera can span many kilometers across and extend hundreds of meters or more in depth. Calderas represent some of the most dramatic topographic features created by volcanic activity.
Formation
Calderas form through subsidence when the structural support provided by magma in the chamber is removed. During large eruptions, magma is expelled rapidly from the reservoir beneath the volcano, leaving a void. The rock above this void cannot support itself and collapses inward, creating a depression. Calderas can also form when magma drains away gradually through underground channels without a major surface eruption. The size and depth of a caldera depend on the volume of magma involved and the strength of the surrounding rock.
Examples and Characteristics
Some of Earth’s largest calderas formed during catastrophic eruptions thousands of years ago. Crater Lake in Oregon, for example, occupies a caldera created by the collapse of Mount Mazama roughly 7,700 years ago. Calderas often contain lakes, smaller volcanic cones, or geothermal features such as hot springs and geysers. Multiple collapses can occur in the same location over geological time, with successive calderas partially overlapping to create complex nested structures.