Caldera
A caldera is a large depression or basin-shaped volcanic landform created when a volcano’s summit collapses inward. This collapse typically occurs following a major eruption that evacuates the magma chamber beneath the volcano, or when magma is withdrawn from the chamber by other means. The resulting depression can be many kilometers across and hundreds of meters deep, substantially larger than the crater found at a typical volcano’s summit.
Formation
Calderas form through subsidence when the structural support beneath a volcano is suddenly removed. During large explosive eruptions, vast quantities of magma are expelled from the underground chamber. As the magma chamber empties, the overlying rock loses support and collapses downward into the void. This process can occur rapidly during an eruption or more gradually as magma cools and contracts over time. The scale of caldera formation is directly related to the size of the magma chamber and the volume of material erupted or withdrawn.
Examples and Characteristics
Notable calderas include Crater Lake in Oregon, formed after the collapse of Mount Mazama approximately 7,700 years ago, and Yellowstone Caldera in Wyoming, which represents one of the world’s largest active volcanic systems. Calderas may contain lakes, be partially refilled by subsequent volcanic activity, or remain as open basins. Some calderas are surrounded by steep walls composed of rock layers exposed by the collapse, providing visible cross-sections of subsurface geology. Calderas differ fundamentally from simple volcanic craters, which are smaller depressions formed by explosive ejection of material rather than collapse.