Aerial View of Crater Lake

May 31, 2007

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Provided and copyright by: Tim Stone
Summary authors & editors: Tim Stone

When Mount Mazama last erupted 7,000 years ago, even the oldest structures in the Fertile Crescent had not been built. Yet Native Americans, who were close enough to observe the eruption yet far enough away to survive it, preserved the eruption story in their legends. The ensuing crater collapse, which formed the caldera that's now Crater Lake in Oregon, occurred when an area between 5 and 6 miles (8 and 9.6 km) in diameter plunged into the magma chamber beneath, after tectonic forces had lowered the chamber's pressure to the point where it could no longer support the mountain. This collapse reduced the altitude of the mountain by 2,500 feet (762 m), and resulted in a 4,000 foot (1,219 m) deep caldera. Over time, the caldera filled with rainwater and snowmelt, while landslides and mild volcanic outflows also partially filled it -- the lake is now some 1,949 ft (594 m) deep.

On the above photo, snow cover provides heightened contrast to the lava flow layers on the flanks of the caldera. Wizard Island is visible on the near side of the lake, a relic of more recent volcanic activity. Photo taken from an altitude of approximately 40,000 ft (12,192 m) on January 17, 2007. See also the Earth Science Picture of the Day for February 15, 2005.

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