Mount Mazama

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Mount Mazama
Crater Lake 2.jpg
Mount Mazama collapsed into a caldera, which was filled with water to form Crater Lake.
Highest point
Elevation 8,159 ft (2,487 m) [1]
Prominence 382 ft (116 m)
Parent peak Mount Scott
Listing Oregon Highest Peaks 76th
Coordinates 42°54′59″N 122°05′04″W / 42.9165186°N 122.0844711°W / 42.9165186; -122.0844711Coordinates: 42°54′59″N 122°05′04″W / 42.9165186°N 122.0844711°W / 42.9165186; -122.0844711[2]
Geography
Parent range Cascade Range[1]
Topo map USGS Crater Lake East
Geology
Mountain type Caldera[1]
Volcanic arc Cascade Volcanic Arc
Last eruption 2850 BCE[1]
Climbing
Easiest route Drive

Mount Mazama is a complex volcano in the Oregon segment of the Cascade Volcanic Arc and the Cascade Range located in the United States. The volcano's collapsed caldera holds Crater Lake, and the entire mountain is located within Crater Lake National Park. Its caldera was created by an eruption 42 times greater than the 1980 eruption of Mount St. Helens.

Mazama's summit was destroyed by a volcanic eruption that occurred around 5677 BC, ± 150 years.[1][3] The eruption reduced Mazama's approximate 12,000-foot (3,700 m) height by about 1 mile (1,600 m). Much of the volcano fell into the volcano's partially emptied neck and magma chamber. At 8,159 feet (2,487 m), Hillman Peak is now the highest point on the rim.

Geography

Mount Mazama lies in Klamath County, within the U.S. state of Oregon,[2] 60 miles (97 km) north of the border between Oregon and California state, in the southern portion of the Cascade Range. Inside the volcano's caldera lies Crater Lake, which has a depth of 1,943 feet (592 m) and thus represents the deepest body of freshwater in the United States.[4][5] Before its caldera-forming eruption, Mazama stood at an elevation between 10,800 to 12,100 feet (3,300 to 3,700 m),[6] placing it about 1 mile (1.6 km) above the lake[4] and making it Oregon's highest peak.[7] The Global Volcanism Program currently lists its elevation at 8,159 feet (2,487 m),[1] while the Geographic Names Information System provides an elevation of 6,174 feet (1,882 m).[2]

Crater Lake National Park

Crater Lake National Park covers an area of 250 square miles (650 km2), 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.[8]

Physical geography

Glaciers formed on the mountain over and over 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 observed at three large glacial canyons on its southern slopes: Kerr Notch, Munson Balley, and Sun Notch.[4] 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 17 miles (27 km) from the rim of Mazama's caldera and there are glacial striations visible at several sites in the area.[9] The most recent period of glacial advance ceased about 27,000 years ago, so by the time Mazama collapsed in its climactic eruption, ice was likely only present at higher elevations.[4]

As a result of global climate change, average snowfall in the Crater Lake area has been decreasing since the 1930s. Crater Lake's mean surface water temperatures have increased about 5 °F (−15 °C) 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.[10]

Ecology

Crater Lake National Park and the area surrounding Mount Mazama range in elevation from 4,000 to 8,929 feet (1,219 to 2,722 m), providing diverse habitats.[11] In the Cascades, the topography and elevation have influenced local climate patterns, also shaping global climate through release of volcanic gas and dust into the atmosphere.[12] The southern region of the park supports ponderosa pine forests, and for elevations from 5,000 to 7,000 feet (1,500 to 2,100 m), mixed coniferous, fir, and hemlock forests are common. Subalpine zones occur above 7,000 feet (2,100 m), often featuring whitebark pine.[11]

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.[13] The immediate surroundings of Mazama continue to recover from the eruption.[12]

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.[14] 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.[14] There are populations of American pikas, snowshoe hares, and white-tailed jackrabbits in the region, in addition to many rodent species. Chipmunks like yellow-pine chipmunks, least chipmunks, Siskiyou chipmunks, and Townsend's chipmunks can be seen, in addition to various beaver species including mountain beavers and North American beavers. The mammals of the National Park area also include various species of squirrel, mice, vole, and gophers, as well as yellow-bellied marmots and North American porcupines. Carnivorous mammals consist of coyotes, red foxes, gray foxes, American black bears, raccoons, martens, fishers, ermines, long-tailed weasels, minks, wolverines, American badgers, western spotted skunks, striped skunks, North American river otters, cougars, and lynxes such as bobcats. Elk, mule deer, and pronghorns can also be found, though more frequently during the summer season.[14]

Bird species in the Crater Lake National Park area include various biological families. Common bird species include hairy woodpeckers, great horned owls, blue grouses, common ravens, dark-eyed juncos, mountain chickadees, red-breasted nuthatches, brown creepers, Clark's nutcrackers, and grey jays, which are visible throughout the year; American kestrels, northern flickers, golden-crowned kinglets, Cordilleran flycatchers, Steller's jays, western tanagers, Swainson's thrushes, hermit thrushes, American robins, and rufous hummingbirds that frequent the area in the summer season; and mountain and western bluebirds in the fall and summer. olive-sided flycatchers and chipping sparrows are common during the spring and summer seasons, while yellow-rumped warblers, pine siskins, and Cassin's finches can frequently be seen during spring, summer, and fall.[11]

In the early 20th century, Bull trout were present in many streams and river throughout the National Park area, particularly the Sun Creek and lower Annie Creek areas. Locals began stocking streams with non-native trout populations, forcing Brook trout to compete for resources and leading to their local extinction in Annie Creek, along with a significant decline in Sun Creek by the end of the 1980s. By 1992, Crater Lake National Park initiated a bull trout conservation project, removing invasive fish populations with electrofishing, snorkeling, and introduction of antimycin A. They also created small barriers to keep new trout from reaching Sun Creek. In 1999, Bull trout were considered a "threatened" species by the Endangered Species Act, though locally, there are now about 2,000 Bull trout in the stream, almost ten times as many as the low point for Bull trout abundance at just 200 fish. The project now works with the state government to expand Bull trout distributions from Sun Creek into neighboring forests with fish barriers and removal of invasive fish species.[15]

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.[10]

Human history

The Klamath Native Americans of the area believed that the mountain was inhabited by Llao, their god of the underworld, also known as the "Chief of the Below World."[16] After the mountain destroyed itself the Klamaths recounted the events as a great battle between Llao and his rival Skell, their sky god,[17] or "Chief of the Above World."[16] Though the narrative has several slightly different iterations, commonly the legend goes that Llao saw a beautiful Klamath woman, the daughter of a chief, and became angry when she refused his offer of immortality if she would be his consort. Furious, Llao emerged from Mazama and threw fire upon the people beneath the mountain, and Skell stood on Mount Shasta, trying to defend the people against Llao's fury. As the earth shook and volcanic rock fell from the sky, two holy men sacrificed themselves to Mount Mazama's crater, and Skell was able to force Llao back into the volcano, which then collapsed on top of him;[16] other accounts tell that Skell smashed the peak on top of Llao.[18] Torrential rain followed, filling in the hole left by Mazama's collapse to form Crater Lake.[16]

Native American people have lived in the area near Mazama for at least 10,000 years.[19] At least part of the surrounding vicinity was occupied by indigenous populations when Mazama resumed activity about 8,000 years ago, following about 20,000 years of dormancy.[4] Most evidence suggests that Mazama served as a camp site, but not a permanent place of habitation.[16] Sagebrush sandals have been discovered to the east of the mountain. These populations faced an increasingly dry climate and the hazards associated with volcanic activity. In civilizations south of Mazama, stories about the volcano's eruption have been transmitted for many generations.[4] Native populations did not tell settlers about the area because it held sacred importance among tribes throughout Oregon and northern California.[16]"Crater Lake: History" (PDF). National Park Service. September 2001. Retrieved February 23, 2018. </ref> Shamans did not allow local Native Americans to look towards Crater Lake,[20] and the Klamath people believed that just looking at Mazama would cause death. Though there are no tribal legends surrounding Crater Lake, some Native Americans still refuse to look at the water.[16]

A few decades after its discovery, Mazama began attracting geological interest.[21] After conducting research at Mazama during the 1880s, in 1902, Joseph S. Diller published a major report with the United States Geological Survey concerning Crater Lake National Park.[22] In the study, he and co-author Horace B. Patton[23] made the claim that Mazama had collapsed instead of being blown apart, the first American geologists to do so.[22] Their work was followed by research led by Howel Williams of the University of California, Berkeley, which was published in 1942. In the paper, Williams mapped the volcano's dacite and andesite lava flow deposits.[24] During the 1980s, Charles Bacon and other USGS geologists expanded on Williams's work, determining more specific details about its caldera formation.[22]

The first known European contact with Mazama occurred in the spring of 1853. Eleven miners from Yreka, California stopped at a mercantile store in Jacksonville, Oregon owned by Isaac Skeeters, boasting that they knew where to find a gold mine called "Lost Cabin." Financed by a successful gold miner named John Wesley Hillman, Skeeters led a team with ten other Oregonians to find the mine. On June 12, they reached Crater Lake, which Skeeters noted had the bluest water he had ever seen, suggesting they name it "Deep Blue Lake." Though their trip failed to procure gold before running low on provisions, they returned with the discovery of the lake, though it was forgotten amidst the absence of gold in that region.[16]

By 1862, a separate group of Oregon prospectors led by Chauncy Nye reached the Crater Lake area. Nye authored an article for the Jacksonville Oregon Sentinel in which he wrote that he had named the depression Blue Lake for its color, the first published description of the lake. During the 1850s, Native Americans and settlers had started to feel hostility towards each other, so Fort Klamath was established in 1863, 7 miles (11 km) to the southeast of the current boundaries of the National Park area. A wagon road was built to the Fort from the Rogue River Valley as a result. On August 1, 1865, the lake was encountered by hunters on the road, and a party of soldiers and civilians went to see the lake after hearing of their observations. Sergeant Orsen Stearns climbed down into the caldera, followed shortly after by Captain F. B. Sprague, who thought they should name the lake "Lake Majesty." The newspaper editor Jim Sutton and a group of people visited Crater Lake in August 1869, using a boat to reach Wizard Island and publishing an article about their experience in the Jacksonville newspaper. Sutton suggested the new name of "Crater Lake".[16]

Mount Mazama received its name from William G. Steel in 1896, the founder of the climbing club The Mazamas, which formed at Mount Hood in 1894.[4] The word comes from an obsolete Native American word meaning "mountain goat",[25][a] derived from an Aztec term to refer to "small deer."[4] Steel gave United States Geological Survey geologist Joseph S. Diller the idea for Mazama's name to help promote national park status for the vicinity by using his organization as the inspiration for the mountain's name. Crater Lake also holds the Klamath name "giiwas".[4] Steel had helped map Crater Lake in 1886 with Clarence Dutton of the United States Geological Survey. The conservation movement in the United States was gaining traction, so Steel's efforts to preserve the Mazama area were achieved on two scales, first with the creation of the local Cascade Range Forest Reserve in 1893, and then on May 22, 1902 with the recognition of Crater Lake National Park.[16]

Geology

At the time of its collapse, Mount Mazama encompassed an area of 150 square miles (400 km2) 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.[6]

Mazama started to grow around 400,000 years ago in the Pleistocene, mainly from lava flows interbedded with some pyroclastic material. These early flows averaged 20 to 30 feet (6 to 9 m) thick and appear to have been emplaced over a few years to a few centuries. Several shield volcanoes were created by these flows, and numerous cinder cones grew in the immediate area (these may or may not be parasitic vents). More explosive eruptions started around 75,000 years ago and built a westward-trending line of composite cones.

Cone building eruptions lasted until around 50,000 years ago when andesite lava flowed down Mazama's north and southwest slopes. Relatively few of the cone-building eruptions issued from the same vent, resulting in a highly complex, approximately 11,000-foot (3,400 m) structure made of overlapping composite cones and shield volcanoes. Consequently, Mazama's base was broader and its sides not as steep as today's Mount Shasta.

After its cone building phase, Mazama lavas became increasingly silica-rich and viscous - two conditions that tend to trap explosive gases. The first major eruption in this new cycle of Mazama's life occurred about 10,000 years later, when dacite flows high on the volcano's southwest face formed a series of domes. These structures were subsequently destroyed by either collapse or steam explosions (see phreatic eruption). Either way, their destruction created large landslides that left deposits at the head of Munson Valley and as far away as Devils Backbone.

Mazama's next major eruptive period occurred between 25,000 and 30,000 years ago and extruded rhyodacite lava (which has a higher silica content than dacite). These thick, slow-moving, pasty flows erupted from a vent on Mazama's northeast flank and solidified to form 600-foot (180 m) high Redcloud Cliff (later cut in two by caldera subsidence) and a dome above what today is Steel Bay.

The volcano then went dormant for roughly the next 20,000 years, while successive ice age glaciers (probably as thick as 1,000 feet (300 m) in troughs) cut large valleys into the mountain's sides. One of the largest glaciers flowed down Munson Valley near the present location of park headquarters, down Annie Creek Valley, and perhaps as far as Fort Klamath. When the last ice age ended 12,000 years ago, those glaciers retreated upslope past the elevation of the current caldera's rim. While Mazama slept, its magma chamber was going through some differentiation, with lighter, more gas- and silica-rich rocks collecting closer to the surface.

Mazama collapse phase 1

Around 5677 BC Mazama awoke from its slumber with explosive rhyodacite eruptions on the northern part of the main summit where Llao Rock now resides. Great quantities of pumice and ash were ejected as a large crater was excavated by the explosions. The tephra was carried by prevailing winds to the east and southeast. Associated with this was a pyroclastic flow that was 1.25 mi (2.0 km) wide, 1,200 feet (370 m) thick at its deepest point, and contained 0.25 cu mi (1.0 km3) of material (later, caldera-forming subsidence cut the partially filled crater in two, exposing it in cross section—today this is called Llao Rock).

One to two hundred years later (based on radiocarbon dating) the last major eruption before the caldera was formed, the Cleetwood flow occurred. This rhyodacite lava flow erupted from a vent near what is now the north caldera rim. The Cleetwood flow was still fluid when the caldera was formed, so it must have erupted just weeks to months beforehand. When Mazama later collapsed into itself, some of the Cleetwood lava backflowed into the caldera.

Mazama's final act started with a large eruption that sent a mile (1.6 km) wide column of hot tephra 5 to 10 miles (8.0 to 16.1 km) into the sky at almost twice the speed of sound. The column collapsed in a series of pyroclastic flows that covered much of the area between and downslope of Llao Rock and Redcloud Cliff. This flow, the first of many, was so hot that it solidified as a welded tuff called the Wineglass Welded Tuff. Flow after flow followed in rapid succession, stressing the ability of Mazama's magma chamber to recharge. The mountain started to sag under its own weight. Concentric ring fractures formed around the volcano, creating convenient conduits for additional volcanic vents.

The eruption entered its final and most destructive cycle with very large and erosive pyroclastic flows erupting from ring fractures all around the volcano. These flows moved out in all directions from Mazama, following river valleys and in some cases not coming to rest for 40 miles (64 km). As the eruptions were occurring, Mazama was imploding.

Mazama collapse phase 2

The collapse and the erosive ring eruptions fed each other—the sinking volcano pushed magma upward, and the erupting material both lubricated the downward subsidence and eroded the sides, making it easier for much of Mazama to sink into the earth. Also, the sudden and dramatic reduction in pressure on the remaining gas charged molten rock in the magma chamber caused it to react by immediately exploding into a super-heated mix of liberated gases and various grades of pulverized and often frothy lava known as a pyroclastic flow. The force of the explosion pulverized previously solidified rock that happened to be nearby or that recently fell into the caldera from the collapse.

Half of 70,000-year-old Hillman Peak was blown away, exposing the cone in cross section. Many glacier-cut canyons were beheaded and now stand as notches in the caldera rim. Notable among these are Kerr Notch, Munson Valley, and Sun Notch.

The last pyroclastic flow of this stage was andesitic scoria, indicating that Mazama was drawing on material from deep within its magma chamber. This layer of material now forms a dark band in ash layers associated with this eruption cycle (it also created the Pumice Desert). A last few dying gasps in the form of a series of relatively weak explosions then deposited a well-bedded layer of pumice lapilli and crystal-rich ash up to 50 feet (15 m) thick on the newly formed caldera rim.

In the end, an estimated 11 to 14 cu mi (46 to 58 km3) of magma escaped from Mazama's magma chamber during this eruptive cycle as approximately 25 cu mi (100 km3) of tephra (magma is compact due to high pressure surrounding it), qualifying the eruption as a VEI 7 event. The magma was replaced by about the same volume of material when most of Mazama fell into its caldera. At that time, Mazama was about 1 mile (1,600 m) shorter than its initial height of approximately 12,000 feet (3,700 m).

Mazama collapse phase 3

Hundreds of square kilometers of the surrounding countryside were covered by material ejected from the collapse and associated eruptions. One pyroclastic flow traveled 40 miles (64 km) from Mazama down Rogue River Valley while another moved north in-between Mount Bailey and Mount Thielsen, moving over Diamond Lake (it finally came to rest in North Umpqua River valley). Winds carried tephra (ash and pumice) from Mazama northeast, where it covered over 500,000 sq mi (1,300,000 km2) including nearly all of Oregon, Washington, northern California, Idaho, western Montana, and parts of Utah, Nevada, Wyoming, Alberta, British Columbia, and Saskatchewan.

Geologists know the exact chemical composition of this tephra (which they call Mazama Ash) and both geologists and archeologists use the distinctive layer it formed in a relative dating technique called tephrochronology. As with all tephra layers, Mazama ash is thickest near its source (20 feet (6.1 m)) and becomes thinner with increasing distance from its source. 70 miles (110 km) northwest it is 1 foot (30 cm) thick.

Deposits of pyroclastic flow material near Mazama remained extremely hot for months, and, in some places, they were more than 250 feet (76 m) deep. Hot gases escaping from the cooling deposits tended to follow vertical channels and emerged at the surface as fumaroles. Over time these gases cemented the channels, which are now exposed as very tall vertical columns and spires of tuff (good examples are along the upper walls of Sand Creek Canyon and Annie Canyon).

Mazama collapse phase 4

All volcanic activity on Mazama since its collapse has been within the caldera. The first significant eruptive period of this phase created an andesite lava platform (the 'central platform') that rises 1,200 feet (365 m) above the caldera floor. Later eruptions created cinder cones such as Wizard Island (c. 6,000 years old and 763 feet (233 m) high) and Merriam Cone and also rhyodacite domes (most of these features are under water).

Over time much of the approximate 4,000-foot (1,200 m) depth of the caldera was filled with volcanic material. Part of the remainder was filled with water from snowmelt and rain to eventually form Crater Lake. Crater Lake reaches a maximum depth of 1,958 feet (597 m), making it the second deepest lake in North America (after Canada's Great Slave Lake). The lake's great depth and purity cause it to absorb all colors of visible light except blue, resulting in its characteristic indigo hue.

Subfeatures

Formed of a complex of stratovolcanoes and shield volcanoes,[1] Mazama is surrounded by monogenetic cinder cones, lava fields, and shield volcanoes made up of calc-alkaline basalt and andesite, tholeiite, and shoshonitic andesite. Varying in age from 600,000 to 40,000 years old, these edifices closely resemble other monogenetic volcanoes in the High Cascades. Extending from the eastern half of Mazama and to the southeast lies a volcanic field consisting of rhyodacitic lava domes and lava flows between 700,000 and 600,000 years old, which encompasses an area of more than 140 square miles (350 km2). This large field is underlain by rhyodacite in its southeastern segment, and is cut by north–south trending normal faults.[6]

Moving from west to northwest, Mazama stratovolcanoes and shield volcanoes grow progressively younger. The oldest, at 400,000 years old, occur at Phantom Ship and Mount Scott, while the youngest can be found at the Hillman Peak stratovolcano, dated to 70,000 years old. There are also andesite flows at the northern rim of Mazama dated to between 50,000 and 40,000 years old.[6] Shield volcanoes near Mazama feature lava flows made of agglutinated mafic andesite, which form sheets about 16-foot (5 m) thick, as well as more deposits from more viscous andesite and dacite magma that reach thicknesses up to 98 feet (30 m).[26] Many of these deposits (both dacitic and andesitic) contain undercooled, crystal-poor segments of andesite, including at Mount Scott and Phantom Cone. Lava and ice interactions are suggested by exposures of glassy breccia in Mazama's caldera, and lava flows cover glaciated lava deposits.[27]

About 70,000 years ago, several silicic, explosive eruptions occurred, including a significant event at Pumice Castle on the eastern wall of Mazama. This formed welded deposits near the vent, also forming non-welded deposits to the south and on the northern part of Mazama.[27] Between 40,000 years ago and Mazama's major eruption, no andesitic or dacitic volcanism took place. However, rhyodacitic magma was erupted at Grouse Hill, Steel Bay, and Redcloud Cliff in the form of pumice and lava flows made of hornblende phyric, or chemically evolved rhyodacite. During this period of the late Pleistocene or early Holocene,[27] lava domes such as those at Sharp Peak, Grouse Hill, and Merriam Point formed,[1] sharing chemical compositions with silica contents at about 70%.[27]

Pyroclastic cones at Mazama include Wizard Island, Bald Crater, Maklaks Crater (also known as Diller Cone) and Forgotten Cone. In addition to its crater, referred to as Williams Crater or the Forgotten Crater, Mazama's various volcanic vents occur at Cleetwood, Llao Rock, and Redcloud, which are located at elevations of 7,005 feet (2,135 m), 8,045 feet (2,452 m), and 7,949 feet (2,423 m), respectively. Nearby cinder cones include Bear Butte, Crater Peak, Desert Cone, Lookout Butte, Pothole Butte, Red Cone, Scout Hill, and Union Peak.[1] There are at least 13 cinder cones within Crater Lake National Park, and at least eleven more in the nearby area. They were fed by a different magma chamber than Mazama, though they likely received magma from basaltic andesite reservoirs in the vicinity. The exception is Williams crater, which erupted basalt and dacite and got silicic lava from the western part of Mazama's magma chamber.[28] Stratovolcanoes in Mazama's vicinity consist of Sentinel Rock, Mount Scott, Phantom Cone, Dutton Cliff, and Danger Bay.[1]

Eruptive history

Mazama formed as a group of overlapping volcanic edifices, which included shield volcanoes and small composite cones.[22] Shield volcanoes fed its expansion with basaltic andesite lava flows that covered large expanses on the slopes of the mountain. Forming lava fountains similar to those observed in Hawaiian eruptions, the shield volcanoes erupted incandescent lava bombs and were deposited on the southern, western, and eastern flanks of the complex. They have average thicknesses of 15 to 20 feet (4.6 to 6.1 m).[22]

Many of the major cone-creating eruptions at Mazama were effusive rather than violently explosive, but explosive eruptions about 70,000 years ago yielded silicic lava that created thick pyroclastic deposits. These deposits include Pumice Castle, an orange edifice at the eastern wall of the caldera, which formed by the fusion of glassy pumice fragments. Similar activity on the northern side of Cloudcap and the eastern segment of Llao Rock that ejected dacitic tephra and pyroclastic rock also formed fused edifices. About 50,000 years ago, a vent at Mazama erupted the Watchman flow, which filled a canyon at the southwestern wall of the complex.[28] From 50,000 to 40,000 years ago, Mazama vents continued to erupt andesite lava flows onto the northern and southwestern slopes and create dacite lava domes on the southern flanks. These domes often collapsed and produced pyroclastic flows that coursed down the southern slope of the volcano, forming deposits up to Devil's Backbone, a craggy volcanic dike that was exhumed when the volcano collapsed.[28]

Throughout its eruptive history, Mazama has produced basaltic andesite, andesite, and dacite lava.[28] About 40,000 years ago, it underwent a dramatic shift to solely rhyodacite lava, which was highly viscous and had a silica content at about 70 percent. Between 30,000 and 25,000 years ago, rhyodacitic eruptions occurred at the complex, yielding pumiceous tephra and lava flows from Grouse Hill, Steel Bay, and Redcloud Cliff. At Redcloud Cliff, a lava flow formed with glassy columns that touched glaciers, creating a large, inverted stone triangle on the eastern rim of Mazama. These same eruptions formed a nearly vertical-walled crater, producing pumice and creating a dome over the Redcloud vent. Grouse Hill's lava flow deposit and lava dome formed at about the same time, about 27,000 years ago. At the end of this eruptive sequence, rhyodacite lava domes formed on the northeastern slopes of the volcano.[29]

Potential hazards

Though the population within 6.2 miles (10 km) of Mount Mazama is only about 50 people, more than 270,000 live within 62 miles (100 km) of the volcano.[1]

See also

Footnotes

  • [a] ^ The word "mazama" also means mountain goat in Spanish.[2]

Notes

  1. ^ a b c d e f g h i j k "Crater Lake". Global Volcanism Program. Smithsonian Institution. Retrieved 2008-12-20. 
  2. ^ a b c d "Mount Mazama". Geographic Names Information System. United States Geological Survey. Retrieved 2006-12-20. 
  3. ^ Zdanowicz, C. M.; Zielinski, G. A.; Germani, M. S. (1999). "Mount Mazama eruption; calendrical age verified and atmospheric impact assessed". Geology. 27 (7): 621–624. Bibcode:1999Geo....27..621Z. doi:10.1130/0091-7613(1999)027<0621:MMECAV>2.3.CO;2. 
  4. ^ a b c d e f g h i Mark, S. R. (September 8, 2017). "Mount Mazama". The Oregon Encyclopedia. Oregon Historical Society. Retrieved February 19, 2018. 
  5. ^ "Deep Water in a Sleeping Volcano". National Park Service. March 22, 2018. Retrieved April 23, 2018. 
  6. ^ a b c d Wood & Kienle 1990, p. 193.
  7. ^ Harris 2005, p. 133.
  8. ^ "Crater Lake National Park". California Volcano Observatory. United States Geological Survey. November 20, 2013. Retrieved February 18, 2018. 
  9. ^ Harris 2005, p. 138.
  10. ^ a b "Climate Change at Crater Lake" (PDF). National Park Service. 2013. Retrieved April 23, 2018. 
  11. ^ a b c "Crater Lake: Checklist of Birds" (PDF). National Park Service. December 2001. Retrieved February 23, 2018. 
  12. ^ a b Green 1998, p. 13.
  13. ^ Green 1998, p. 11.
  14. ^ a b c "Crater Lake: Checklist of Mammals" (PDF). National Park Service. December 2001. Retrieved April 24, 2018. 
  15. ^ "Bull Trout Conservation and Recovery". National Park Service. February 28, 2015. Retrieved April 23, 2018. 
  16. ^ a b c d e f g h i j "Crater Lake: History" (PDF). National Park Service. September 2001. Retrieved February 23, 2018. 
  17. ^ "Volcanoes in Historical and Popular Culture: Legends and Mythology". Cascades Volcano Observatory. USGS. Archived from the original on 2014-02-02. Retrieved 2008-12-19. 
  18. ^ Thomas 2007, p. 49.
  19. ^ Harris 2005, p. 134.
  20. ^ Topinka, L. (May 21, 2018). "Volcanoes in Historical and Popular Culture Legends and Mythology". United States Geological Survey. Retrieved April 23, 2018. 
  21. ^ Harris 2005, pp. 135–136.
  22. ^ a b c d e Harris 2005, p. 136.
  23. ^ Diller & Patton 1902, p. 1.
  24. ^ Keroher 1966, p. 2633.
  25. ^ Lewis, C. (c. 1901). "The Disappearance of Mount Mazama". Pearson's Magazine (archived by A Place Called Oregon). Retrieved 2008-12-20. 
  26. ^ Wood & Kienle 1990, pp. 193–194.
  27. ^ a b c d Wood & Kienle 1990, p. 194.
  28. ^ a b c d Harris 2005, p. 139.
  29. ^ Harris 2005, p. 140.

References

  • Green, R. A. (1998). Mount Mazama and Crater Lake : a study of the botanical and human responses to a geologic event (Thesis). Oregon State University. Retrieved April 23, 2018. 
  • Harris, Ann G.; Tuttle, Esther; Tuttle, Sherwood D. (1997). Geology of National Parks (5th ed.). Iowa: Kendall/Hunt Publishing. ISBN 0-7872-5353-7. 
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