Мазама: История вулкана и образование озера Кратер-Лейк

Complex volcano in the Cascade Range

Mount Mazama (Tum sum ne in the Native American language Klamath) is a complex volcano in the western U. S. state of Oregon, 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 mile (97 km) 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 (Giiwas in the Native American language Klamath). Mount Mazama originally had an elevation of 12000 feet (3658 m), but following its climactic eruption this was reduced to 8157 feet (2486 m). Crater Lake is 1943 feet (592 m) 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 12000 feet (3658 m) height by about 1 mile (2 km). 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.

Mount Mazama is in Klamath County, within the U. S. state of Oregon, 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 1 mile (2 km) above the lake;

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.

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 (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 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 (section) 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 8934 feet (2723 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 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 12000 feet (3658 m) 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 Mazama edifice had an estimated volume of , though it may have exceeded taking glacial erosion into account. After the climactic eruption, Mazama's peak was completely destroyed, replaced by a depression with a depth of 4000 feet (1219 m) surrounded by cliffs. The volume of magma erupted from Mazama during this eruption was 14 cubic miles (61 km3). The lava produced was zoned vertically according to arrangement within the source magma chamber, and was calc alkaline in composition. It consisted of roughly 90 percent uniform rhyodacitic pumice, which contained about 10 percent phenocrysts, the rest made up of crystalline andesite scoria and mafic crystals. The total eruptive volume adds up to 42 cubic miles (176 km3) which would make it over twice the size of the Mazama ash. Mazama's climactic eruption was one of the largest eruptions during the Holocene epoch. Considering Mazama's eruptive output within the past 420,000 years, it may have produced more than of eruptive volume, making it either the third or fourth most productive Quaternary volcanic center in the Cascade Range. The eruption had a Volcanic Explosivity Index of 7, as determined from eruption cloud height, eruptive volume, and qualitative observations.

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 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 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 1200 feet (366 m) above the floor of Crater Lake; just two percent of Wizard Island sits above the water surface. 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 , 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 magma than are known to be available within the Mazama vicinity. Landslides could flood adjacent shoreline regions, but they are not likely to induce failure of the caldera's walls, as they rise more than 500 feet (152 m) above the lake's surface. Earthquakes from the nearby West Klamath Lake fault zone could reach magnitudes up to 7.0 on the Richter scale, but these only occur every 3,000 to 10,000 years; they could generate tall waves by creating landslides. Though local earthquakes from volcanic activity would create motion in the lake, they would likely only reach maximum magnitudes of 5.0 on the Richter scale. Crater Lake is poorly monitored, and not highly active seismically among the Cascade volcanoes. The largest earthquake threat originates from the Cascadia subduction zone, which could produce earthquakes with a magnitude of 8 or 9 that could lead to huge waves in Crater Lake. Though the population within of Mount Mazama is only about 50 people, more than 270,000 live within of the volcano. traveling at speeds from Landslides could threaten visitors to the national park or researchers by creating tsunami sized waves, also potentially damaging infrastructure surrounding the lake.

Studies of heat flow and the water chemistry in Crater Lake and the alteration of rocks older than 120,000 years ago suggest that hydrothermal areas exist in the Mazama vicinity. Most springs show similar chemistry, from the weathering of volcanic glass and clinopyroxene. These features probably formed due to processes related to residual heat from the magma chamber that produced the climactic Mazama eruption 7,700 years ago. The lake shows convective mixing that cycles every three years as thermal fluid moves into the lake through its floor, creating thermal springs that formed silica spires with heights up to As a result, the California Energy Company drilled two geothermal exploration wells: the MZI 11A with a depth of to the east of the national park barrier at the Scott Creek Drainage, and the MZII 1 with a depth of to the south of the same boundary and to the east of Annie Creek. The maximum temperature they have observed at the southern well is 40 °C (104 °F), while the maximum temperature was 130 °C (266 °F) at the eastern well. The convective heat discharge in Crater Lake marks the third largest in the Cascades, after the Austin Hot Springs and at Lassen Volcanic National Park. Scientists from the United States Geological Survey think that sources for geothermal energy use exist at Mazama and Crater Lake.

Crater Lake National Park and the area surrounding Mount Mazama range in elevation from , providing diverse habitats. Ecological disturbances tend to cause decreasing damage with increasing distance from the source, but volcanic eruptions can lead to more uniform patterns of disruption for their surrounding landscapes. The immediate surroundings of Mazama continue to recover from the eruption. There are more than 50 mammal species in Crater Lake National Park. Opossum species such as the Virginia opossum can be found infrequently, while shrew and mole species in the park area include marsh shrews, Pacific shrews, American water shrews, fog shrews, Trowbridge's shrews, vagrant shrews, American shrew moles, and broad footed moles. Bats frequently sighted within the park area include the little brown bat, hoary bat, and big brown bat, while the California myotis, silver haired bat, Yuma myotis, long eared myotis, long legged myotis, and pallid bat are more rare. Climate change threatens the American pika populations in the Crater Lake area, as they cannot tolerate warm weather because their fur does not release heat efficiently. Climate change might be diminishing their food supply via disturbances of vegetation growth patterns. At least three pika populations in Oregon have disappeared within the past few decades. Likewise, as a result of climate change, mountain pine beetle infestations have become more frequent among Whitebark pines on the rim of Crater Lake and present on nearby peaks. The National Park Service estimates that roughly half of the whitebark pines in Crater Lake National Park have died or are dying. After the mountain destroyed itself the Klamaths recounted the events as a great battle between Llao and his rival Skell, their sky god, or "Chief of the Above World." and the Klamath people believed that just looking at Mazama would cause death. Some Native Americans still refuse to look at the water. The word comes from a Native American word meaning "mountain goat",NoteTag|The word "mazama" also means mountain goat in Spanish. No lodges, gas stations, or camping areas remain open from October through late May. Popular activities within Crater Lake National Park include biking, fishing, cross country skiing, and snowshoeing.