This is an image of Crater Lake in Oregon, USA.
Click on image for full size
Image from: U.S. Geological Survey
Mt. Mazama was once among a group of volcanoes stretching along the coast of Washington and Oregon. This group of volcanoes includes Mt. Hood
, Mt. Rainier
, and Mt. St. Helens
6850 years ago, Mt. Mazama erupted for a final time. The eruption occured over a number of months, and produced major outbursts of ash, lava, and hot vapors.
Following this series of eruptions, the cone of the volcano collapsed into the ground, and Mt Mazama became dormant except for activity which formed a small cinder cone in the center (shown in this picture). The collapsed volcano filled with water and became what we now know as Crater Lake.
The Indians who lived near Mt. Mazama when it fell have a different story of what caused the mountain to collapse.
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