landform-geography

Calderas

The word caldera is derived from the Spanish word for cauldron . A caldera is a geological feature , the remnants of a volcano that has collapsed , typically by hundreds or even thousands of meters , into itself . Many calderas are d with water , whereupon they are typically regarded as lakes

A caldera typically forms as a result of one eruption or a series of eruptions . When a volcano erupts because of pressure in its magma chamber , the structure of the volcano may become unstable the release of pressure from the volcano 's

magma chamber causes the structure to lose the structural support from the pressure of the magma , and thus it may not be able to support its own weight . When this happens a ring of fractures will form on the perimeter of the volcano cone , and this fractures may in turn become additional vents , thereby further hastening the collapse of the volcano cone

Crater Lake caldera , Oregon . The caldera that contains the lake is 1 .2 kilometers deep , formed about 6900 years ago when the volcano Mount Mazama collapsed . All eruptions have since then occurred only in the caldera (USGS image

Some calderas are formed by explosive events . These calderas are very active volcanically . Underneath these explosive calderas may be magma that is silica-rich , making the magma is very viscous . Viscous magma is more likely to contain trapped gases , which expand very quickly upon nearing the earth 's surface because of the decreased pressure

This sudden formation of bubbles is what causes volcanic explosions that empty a volcano 's magma chambers and that can result in a caldera Highly pressurized magma contains dissolved gases that , once near the surface , will come out of the solution to form bubbles . When the gases come out of the solution and expand faster that they can escape the magma , an explosion occurs . The rapidly expanding gases causes explosions that release magma and volcanic ash , affecting large areas around the caldera

These silica-rich calderas usually expel very large amounts of magma from hundreds or thousands of cubic kilometers in one instance . Because of their very violent nature , caldera-forming eruptions may result in great surface damage and a significant drop of worldwide atmospheric temperature

A notable example is the Yellowstone Caldera . Its eruption estimated to have occurred 640 ,000 years ago released about 1000 cubic kilometers of magma , and covered half of North America in up to two meters of material

Diagram of the Yellowstone Caldera (USGS image

However , some calderas are formed differently from explosive calderas Non explosive calderas are created when magma rises slowly , so that gases can escape more gently and no explosive eruptions occur . These non-explosive calderas (also known as subsidence calderas ) are fed by significantly less viscous magma compared to explosive calderas because of the magma 's low silica content . These calderas are formed because of drainage from the volcanoes magma chamber through lava flow instead of explosions

Calderas are the world 's largest volcanic structure , so large that many have...