page_title: Mount Mazama
section_title: Recent activity and potential hazards
hierarchical_section_title: Mount Mazama / Eruptive history / Recent activity and potential hazards
caption_attribution_description: Wizard Island - Crater Lake Oregon
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: Since the climactic eruption 7,700 years ago, all eruptive activity at Mazama has occurred within the caldera. After the caldera formed, the original crater was widened by avalanches from the walls. These gave a scalloped profile to the caldera, such as the coves at Llao Bay, Steel Bay, and Grotto Cove. The Chaski slide, for example, the most prominent landslide detectable on the caldera wall, occurred long after the formation of the crater. Located on the southern side, it contains lava blocks between 850 to 1,400 feet (260 to 430 m) in length, many of which now reside underwater on the floor of Crater Lake. As the crater filled with landslides, lava, and water, the caldera's appearance changed over time. New cones and lava fields have formed inside the caldera, all of which have been submerged except for Wizard Island. Mapping the caldera floor with high-resolution multibeam echo sounders, vehicle-motion sounders and navigators, and a dual-differential global positioning system (DGPS), scientists from the US government and universities detected volcanoes and landslide deposits under the water. Between 7,700 and 7,200 years ago, the central lava platform, the Merriam Cone, and Wizard Island were produced, as well as lava flows. These eruptions produced 1 cubic mile (4.2 km³) of andesitic lava, half of that in the Wizard Island cone. Wizard Island lava interacted with water to form breccia piles, and as the water levels rose, only the top of the Wizard Island edifice stayed above the water. The edifice has a lavaberg shape, as it sits above a larger, ovular pedestal rising 1,200 feet (370 m) above the floor of Crater Lake; just two percent of Wizard Island sits above the water surface. At the summit of the above-water cone, a small lava flow from a lava fountain appears, located on the southwestern flank. There is also a volcanic plug poking out of the crater floor as a body of dark lava. Lava blocks with diameters of 6 to 7 feet (1.8 to 2.1 m) can be seen along the rim of the crater, possibly produced from later stages of cone-building eruptions that created Wizard Island. The central platform was created by a similar vent eastward of Wizard Island, made up of effusive lava that created lava fields northward and eastward of its vent. Merriam cone does not have a summit crater, but rises to 1,300 feet (400 m) above the northern lake floor. Merriam cone was produced underwater, and was probably formed at the same or similar time as Wizard Island and the central platform.
  Mazama was last active about 4,800 years ago, when an eruption took place near Wizard Island's eastern base. This eruption took place underwater, and it produced viscous lava that created a rhyodacite lava dome, about 2,400 years after the first period of postcaldera activity. Given that Mazama has had periods of sporadic eruptions for 420,000 years, the United States Geological Survey thinks that it is "virtually certain" that Mazama will erupt again in the future. Mazama is considered dormant, but it remains monitored by the United States Geological Survey Cascades Volcano Observatory. Future eruptions would likely take place near the western side of the complex and within the caldera rim; they could occur underwater. The ejection of lava rich in gas from shallow water could produce huge ash columns, but submarine eruptions at deeper depths may decrease the explosiveness of the event. Nonetheless, the rapid mixing of water and lava could produce dangerous pyroclastic surges, which are more gaseous and less solid than pyroclastic flows. Such flows could pass over topographic barriers, move rock fragments at 800 feet per second (240 m/s), and travel several miles from their vent. Mazama is unlikely to produce mudflows far from the caldera, though a nearby vent outside the caldera could erupt and mix with snow. Eruptions are unlikely to produce waves that extend beyond Crater Lake, but powerful explosions could produce tall waves in the caldera. An eruption as explosive as the one 7,700 years ago is unlikely given that it would require larger volumes of ma
caption: Postcaldera activity has included the production of the Wizard Island cinder cone volcano in Crater Lake
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