Mount Mazama
Mount Mazama is a complex volcano in the western U.S. state of Oregon, in a segment of the Cascade Volcanic Arc and Cascade Range. The volcano is in Klamath County, in the southern Cascades, north of the Oregon–California border. Its collapse, due to the eruption of magma emptying the underlying magma chamber, formed a caldera that holds Crater Lake. Mount Mazama originally had an elevation of approximately, but following its climactic eruption this was reduced to. Crater Lake is deep, the deepest freshwater body in the U.S. 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 height by about. 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 U.S. Geological Survey says eruptions on a smaller scale are likely, which would pose a threat to its surroundings.
Native Americans have inhabited the area around Mazama and Crater Lake for at least 10,000 years and the volcano plays an important role in local folklore. European-American settlers first reached the region in the mid-19th century. Since the late 19th century, the area has been extensively studied by scientists for its geological phenomena and more recently for its potential sources of geothermal energy. Crater Lake and Mazama's remnants sustain diverse ecosystems, which are closely monitored by the National Park Service because of their remoteness and ecological importance. Recreational activities including hiking, biking, snowshoeing, fishing, as well as cross-country skiing are available; during the summer, campgrounds and lodges at Crater Lake are open to visitors.
Geography
Mount Mazama is in Klamath County, within the U.S. state of Oregon, north of the border with California. It lies in the southern portion of the Cascade Range. Crater Lake sits partly inside the volcano's caldera, with a depth of ; it is the deepest body of freshwater in the United States and the second deepest in North America after Great Slave Lake in Canada. Before its caldera-forming eruption, Mazama stood at an elevation between, placing it about above the lake; this would have made it Oregon's highest peak. The Global Volcanism Program currently lists its elevation at.Crater Lake National Park
Crater Lake National Park covers an area of, including forest areas, alpine terrain, the Crater Lake, and the vast majority of Mount Mazama. A wilderness area, it was dedicated in 1902 and is overseen by the National Park Service. It receives about 500,000 visitors each year, and these tourists can go hiking, take bike, ranger-guided, and trolley tours, swim, fish, camp, and participate in other recreational activities. While the park area remains open throughout the year, certain roads and facilities close in the winter season.Physical geography
There was frequent glacier formation on the mountain as Mazama developed. They carved trenches in the flanks of the volcano in addition to U-shaped valleys under the base of the volcanic cone. These can be seen at three large glacial canyons on its southern slopes: Kerr Notch, Munson Valley, and Sun Notch. Whenever eruptions took place in the presence of ice, lava was chilled by glaciers, creating glassy talus deposits. Sometimes, the lava coursed into areas previously carved by glaciers like at Sentinel Rock, filling canyons with volcanic rock. Moraines occur up to from the rim of Mazama's caldera, and there are glacial striations visible at several sites in the area. When the climactic eruption occurred, the climate was warm and dry, and the most recent period of glacial advance ceased about 27,000 years ago, so by the time Mazama collapsed, ice was likely only present at higher elevations. Using argon geochronology and paleoclimatic records, scientists have identified that the Sand Creek, Sun Creek, and Annie Creek canyons were carved by the advance of ice over lava flows, pushing debris towards Klamath Marsh and Klamath Graben or nearby rivers. A glacial cirque can be seen on Mount Scott's northwestern flank, and glacial till occurs on Mazama's slopes, especially on the western slopes and at lower elevations. Till and fluvial sediments occur in the caldera walls, forming particularly thick deposits under Roundtop and Wineglass. Many lava flows that were glaciated have since been covered by more recent lava flows.Crater Lake formed from a network of lakes and ponds, eventually reaching a depth of. Lake levels rose while the Wizard Island landform inside the crater was forming. Water interacted with lava flows to form pillow lava. Because of climate change patterns over time, Crater Lake's surface level has changed, dropping as much as for example at the beginning of the 20th century. The water from precipitation nearly equals water lost to evaporation and drainage, most leakage taking place at the Wineglass deposit at the northern side of the crater, without which the lake would likely have overflowed at the northern side.
Average snowfall in the Crater Lake area has been decreasing since the 1930s. Crater Lake's mean surface water temperatures have increased about since the 1960s. Though this may eventually cause algae to grow and obscure the water, Crater Lake remains one of the cleanest bodies of water in the world.
Geology
Produced by the subduction of the Juan de Fuca Plate at the Cascadia subduction zone, 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. It 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 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 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 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 from Timber Crater to the Big Bunchgrass shield volcano. This includes 175 Quaternary volcanic vents within a belt that ranges from 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. 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, 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 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 state, and concluded that Mazama stood at pre-collapse, which has been accepted as the standard estimate by geologists. By the Holocene, the Mazama volcano was made up of several, clustered peaks with Mount Scott on the eastern end and Hillman Peak on the far west side. The volcanoes likely rose in elevation from east to west, and they also featured volcanic cones and lava domes on their southern flanks. Glacial horns like the Watchman lava flow were also present, and the mountain may or may not have sustained glaciers close to the summit. At the time of its collapse, Mount Mazama encompassed an area of and represented one of the major volcanoes in the High Cascades branch of the greater Cascade Range. It was the largest volcanic edifice between Mount Shasta in California and the Three Sisters complex in Oregon. Before the eruption, it had been significantly altered by glacial erosion, which carved U-shaped valleys on its southern and southeastern slopes. The northern and western sides of the caldera do not show prominent evidence of glacial erosion, since they feature lava flows that only underwent alteration by late Pleistocene epoch glacial motion. Outside of the caldera, most hills show evidence of glacial alteration except those from the Holocene epoch and low elevation landforms including Pleistocene lava domes and cinder cones. Mount Scott has also been heavily eroded by ice, and the Union Peak volcano now consists only of a pyramidal horn.
Though it now has dimensions of and a width of, scientists think the original collapse diameter was. It now includes several small lava domes and cinder cones, including Wizard Island and the underwater volcano Merriam Cone. The highest elevation in the Mazama Complex is now Mount Scott, at an elevation of, with a relief of above Crater Lake's surface waters. Except for the tallest slopes of the complex, all cones have been covered with deposits from the climactic eruption at Mazama 7,700 years ago. Scientists now use the exposed contents of the caldera rim wall to investigate eruptions and mapping the eruptive history of the region. Throughout its known eruptions, Mazama has produced 43 percent rhyodacite, 42 percent andesite, 15 percent dacite, and less than 1 percent basaltic andesite. All of the rhyodacite has been produced within the past 30,000 years of activity, suggesting that regional and local distribution of compositions were not uniform over time. Andesite and dacite lava flows from the volcano usually have plagioclase as their major phenocryst, though augite and hypersthene are also present, the latter more abundant. Olivine form minor phenocrysts, which are found throughout lava flows from Mazama, and hornblende can be found in some andesite lava flows. Basalt and mafic andesite lava flows from Mazama and nearby eruptive vents have relatively higher amounts of olivine and lack hypersthene, and the mafic andesite deposits display textures that indicate they underwent greater mixing than andesite and dacite deposits.