Vanished Volcano Mount Mazama - Fort Klamath, OR - Places of Geologic Significance on Waymarking.com

Most of the mountain collapsed following a major eruption approximately 7,700 years ago.

Its collapse, due to the eruption of magma emptying the underlying magma chamber, formed a caldera that holds Crater Lake. The mountain is in Crater Lake National Park. Mount Mazama originally had an elevation of 12,000 feet (3,700 m), but following its climactic eruption this was reduced to 8,157 feet (2,486 m).

Mount Mazama formed as a group of overlapping volcanic edifices such as shield volcanoes and small composite cones, becoming active intermittently until its climactic eruption 7,700 years ago. This eruption, the largest known within the Cascade Volcanic Arc in a million years, destroyed Mazama's summit, reducing its approximate 12,000-foot (3,700 m) height by about 1 mile (1,600 m). Much of the edifice fell into the volcano's partially emptied neck and magma chamber, creating a caldera. The region's volcanic activity results from the subduction of the offshore oceanic plate, and is influenced by local extensional faulting. Mazama is dormant, but the US Geological Survey says eruptions on a smaller scale are likely, which would pose a threat to its surroundings.

Mazama is underlain by the Quaternary High Cascade basalt and mafic (rich in magnesium and iron) andesite to the west and southwest, with high-volume rhyodacite lava flows from 600,000 to 700,000 years old underlying Mazama deposits to the south, southeast, east, and northeast.[24] It is a major Cascade volcano, and is at the intersection of the Cascade Range and Klamath graben, the north–northwest trending basin also surrounded by fault zones. The Basin and Range Province lies to the east.

After Newberry Volcano, Mazama is the second largest Quaternary volcanic edifice in Oregon, and the most voluminous.

Mazama is the newest of the Quaternary calderas in the Cascade Volcanic Arc, which also include the Newberry calderas and the caldera at the Medicine Lake Volcano.

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