Mount Mazama created Oregon’s Crater Lake when its summit collapsed after a major eruption about 7,700 years ago.
Before the eruption, Mount Mazama was a much taller composite volcano. The event emptied enough magma from beneath the summit that the overlying rock collapsed, forming a broad caldera. Rain and snow later filled the depression, producing the intensely blue lake known today as Crater Lake.
Crater Lake is the deepest lake in the United States, reaching 594 metres. Wizard Island, a cinder cone rising from the lake, formed after the main caldera collapse during later volcanic activity.
Mount Mazama is often confused with Crater Lake because the modern landscape is usually named for the lake rather than the volcano. The volcano itself is the geological structure that collapsed; Crater Lake is the water-filled caldera left behind.