page_title: Mount Mazama
section_title: Geology
hierarchical_section_title: Mount Mazama / Geology
caption_attribution_description: English: 180-degree panoramic photograph of Crater Lake from the top of nearby Mount Scott, looking west. The panorama was created from 34 separate images. Two snow-covered peaks can be seen in the distance: to the right of the lake is Mt. Thielsen, and in the far left of the photo is Mt. McLoughlin.
context_page_description: Mount Mazama is a complex volcano in the state of Oregon, United States, in a segment of the Cascade Volcanic Arc and Cascade Range. Most of the mountain collapsed following a major eruption approximately 7,700 years ago. The volcano is in Klamath County, in the southern Cascades, 60 miles north of the Oregon-California border. Its collapse 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, but following its climactic eruption this was reduced to 8,157 feet. Crater Lake is 1,943 feet deep, the deepest freshwater body in the US and the second deepest in North America after Great Slave Lake in Canada.
  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 height by about 1 mile. Much of the edifice fell into the volcano's partially emptied neck and magma chamber, creating a caldera.
context_section_description: Produced by the subduction of the Juan de Fuca tectonic plate, which moves slowly in a northeastward direction with the Gorda tectonic plate under the North American tectonic plate, Mazama is part of the Cascade Volcanic Arc that stretches from northern California to southern British Columbia. Mazama sits within a region of crustal extension marked by fault zones, including north–south-trending normal faults such as the Annie Spring fault within the West Klamath Lake fault zone, which might produce damaging earthquakes. Likewise, the Red Cone Spring fault cuts through basaltic andesite deposits at Red Cone from 35,000 years ago; together, the two faults move at an average rate of 0.012 inches (0.3 mm) each year. There do not appear to be faults present in the Crater Lake caldera wall, but the volcano induced a stress field in the upper crust nearby.
  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. It is a major Cascade volcano, and is located 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. Mazama lies within the broad segment of the Cascades arc, where smaller volcanoes are common because of melting patterns of the Earth's mantle within the region. Erupting magma that ranged from high-alumina olivine tholeiite to magnesian basaltic andesite, these volcanoes show increased contents of subduction-produced or melted fluids that mixed with another magma chamber in the mantle. These magmas vary from 47.6 percent to 73.2 percent silicon dioxide.
  Mazama and Crater Lake form part of the Mazama reach of the Oregon Cascades, which stretches for 25 miles (40 km) from Timber Crater to the Big Bunchgrass shield volcano. This includes 175 Quaternary volcanic vents within a belt that ranges from 16 to 19 miles (25 to 30 km) in width, which has a high vent density with many shields and monogenetic volcanic centers. After Newberry Volcano, Mazama is the second largest Quaternary volcanic edifice in Oregon, and the most voluminous, with an overall volume of 29 cubic miles (120 km³). 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. Quaternary monogenetic volcanism throughout Oregon's High Cascades includes cinder cones, lava fields, and small shield volcanoes, which have produced lava ranging from low-potassium, high-alumina olivine tholeiite to medium-potassium calc-alkaline basalt, basaltic andesite to shoshonitic basaltic andesite.
  The Mazama volcanic complex originally formed as a cluster of overlapping edifices. Made up of shield volcanoes and small stratocones, it had an irregular shape. Mount Scott, at a height of 8,934 feet (2,723 m), marks the oldest visible remnant of this original cluster. Scott was the first of the composite volcanoes that created the Mazama complex, formed by a quick and active cone-building phase and becoming inactive long before the most recent eruption at Mazama. With time, eruptive activity moved to the west, creating the Applegate Peak and Garfield Peak cones on the southern flanks of the volcanic center. Hawaiian eruptions from neighboring shield volcanoes also built up Mazama, producing basaltic andesite lava flows that ranged from 15 to 20 feet (4.6 to 6.1 m) on average in thickness. These flows, present on the southern, western, and eastern walls of Mazama's caldera, also contained lava bombs. Viscous eruptions of andesitic lava that reached thicknesses of several hundred feet further built up Mazama's cones, creating a solid, dense interior rich with angular lava blocks.
  Research by Howel Williams superimposed the Crater Lake caldera on other Cascade stratovolcanoes including Mount Shasta in California and Mount Rainier in Washington sta
caption: Crater Lake and the Mazama vicinity, as seen from Mount Scott
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