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What happens to create a caldera?

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A caldera forms as a volcano's magma chamber empties, resulting in a loss of support for the earth above it. These bowl-shaped depressions can range in size from a few hundred meters to several kilometers wide. They are generally caused by large volcanic eruptions.

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Calderas and craters are not to be confused. Craters are created by an explosion of rock upward from a volcanic blast. Calderas are created by a sinking of the earth into the empty magma chamber left behind after the eruption.

The intense pressure of trapped gases in the magma chamber bulges the earth above and creates vents and cracks in the land. Once this pressure is released, the earth collapses back into the now empty space from which the pressure appeared. Sometimes the land collapses irregularly, leaving behind an uneven depression.

Eruptions large enough to create calderas have not occurred during recorded human history. However, geologic evidence indicates massive eruptions in Earth's past creating calderas such as the one found in Yellowstone National Park. The Yellowstone Caldera lies above a magma chamber 24 to 48 miles wide. The last eruption of this magma chamber occurred approximately 640,000 years ago and was 1,000 times larger than the eruption of Mt. Saint Helens.

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