What Is A Caldera?
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A caldera is a large, bowl-shaped depression formed when a volcano's magma chamber empties during a major eruption and the overlying rock collapses inward. Calderas range from a few miles to dozens of miles across and represent the most catastrophic type of volcanic eruption. Yellowstone, Crater Lake, and Santorini are famous examples.
Calderas are some of the most spectacular and dangerous volcanic features on Earth. Despite often being mistaken for craters (which are smaller and form differently), calderas are huge collapse features that mark the sites of the most catastrophic eruptions known. They can be tens of miles across and many hundreds of feet deep. Famous calderas include Yellowstone, Crater Lake, Santorini, and the Aira Caldera that contains Sakurajima volcano.
How does a caldera form?
Calderas form when a volcano's magma chamber empties dramatically during a large eruption, removing the support that held up the overlying rock. With the chamber suddenly empty, the rock above collapses downward into the empty space, creating a roughly circular depression at the surface. The collapse can happen during a single catastrophic eruption (sudden caldera formation) or progressively over multiple eruptions. The largest calderas form during super-eruptions, where the magma chamber may have been hundreds of cubic miles in size. The Yellowstone caldera formed this way during a super-eruption 631,000 years ago.
What is the difference between a caldera and a crater?
Craters and calderas are easily confused but very different features. A crater is a relatively small depression at the top of a volcanic vent, typically a few hundred feet to a mile or so across, formed by eruption activity and erosion at the vent. A caldera is a much larger depression, typically miles to tens of miles across, formed by collapse rather than by direct eruption activity. Many large calderas contain smaller craters within them where post-collapse volcanic activity has occurred. Crater Lake, for example, is a caldera that contains the volcano Wizard Island as a post-collapse cone.
What are famous calderas?
Yellowstone Caldera in Wyoming is one of the largest calderas in the world, about 45 by 28 miles, formed by three super-eruptions over 2.1 million years. Crater Lake in Oregon is a 5-mile-wide caldera that formed about 7,700 years ago when Mount Mazama collapsed; the depression filled with water to create the deepest lake in the US. Santorini in Greece is a flooded caldera formed by a Bronze Age eruption around 1600 BCE. Aira Caldera in Japan contains the active Sakurajima volcano. Long Valley in California, Taupo in New Zealand, and Toba in Indonesia are also major caldera systems.
Can calderas still erupt?
Yes, calderas remain volcanically active because they still have magma chambers underneath, even if smaller than the ones that produced the original caldera. Yellowstone has ongoing geothermal activity (hot springs, geysers, hydrothermal explosions) and could potentially produce another super-eruption, though probably not for tens or hundreds of thousands of years. Aira Caldera's Sakurajima erupts multiple times daily. Campi Flegrei near Naples has had recent ground deformation that worries volcanologists. Most calderas have smaller post-collapse eruptions long after the catastrophic event that formed them.
A caldera is a large depression formed when a volcano's magma chamber empties and the rock above collapses inward. Yellowstone, Crater Lake, and Santorini are famous calderas, with Yellowstone being one of the world's most monitored geological features. Larger and very different from craters, calderas mark the sites of Earth's most catastrophic volcanic eruptions.
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