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Glacial Lake Missoula

Glacial Lake Missoula

Overview
Glacial Lake Missoula was a prehistoric proglacial lake
Proglacial lake
In geology, a proglacial lake is a lake formed either by the damming action of a moraine or ice dam during the retreat of a melting glacier, or by meltwater trapped against an ice sheet due to isostatic depression of the crust around the ice...

 in western Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

 that existed periodically at the end of the last ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

 between 15,000 and 13,000 years ago. The lake measured about 7770 square kilometres (3,000 sq mi) and contained about 2100 cubic kilometres (503.8 cu mi) of water, half the volume of Lake Michigan
Lake Michigan
Lake Michigan is one of the five Great Lakes of North America and the only one located entirely within the United States. It is the second largest of the Great Lakes by volume and the third largest by surface area, after Lake Superior and Lake Huron...

.

The Glacial Lake Missoula National Natural Landmark is located about 68 miles northwest of Missoula, Montana
Missoula, Montana
Missoula is a city located in western Montana and is the county seat of Missoula County. The 2010 Census put the population of Missoula at 66,788 and the population of Missoula County at 109,299. Missoula is the principal city of the Missoula Metropolitan Area...

 at the north end of the Camas Prairie Valley, just east of Montana Highway 382 and Macfarlane Ranch.
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Encyclopedia
Glacial Lake Missoula was a prehistoric proglacial lake
Proglacial lake
In geology, a proglacial lake is a lake formed either by the damming action of a moraine or ice dam during the retreat of a melting glacier, or by meltwater trapped against an ice sheet due to isostatic depression of the crust around the ice...

 in western Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

 that existed periodically at the end of the last ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

 between 15,000 and 13,000 years ago. The lake measured about 7770 square kilometres (3,000 sq mi) and contained about 2100 cubic kilometres (503.8 cu mi) of water, half the volume of Lake Michigan
Lake Michigan
Lake Michigan is one of the five Great Lakes of North America and the only one located entirely within the United States. It is the second largest of the Great Lakes by volume and the third largest by surface area, after Lake Superior and Lake Huron...

.

The Glacial Lake Missoula National Natural Landmark is located about 68 miles northwest of Missoula, Montana
Missoula, Montana
Missoula is a city located in western Montana and is the county seat of Missoula County. The 2010 Census put the population of Missoula at 66,788 and the population of Missoula County at 109,299. Missoula is the principal city of the Missoula Metropolitan Area...

 at the north end of the Camas Prairie Valley, just east of Montana Highway 382 and Macfarlane Ranch. It was designated as a National Natural Landmark
National Natural Landmark
The National Natural Landmark program recognizes and encourages the conservation of outstanding examples of the natural history of the United States. It is the only natural areas program of national scope that identifies and recognizes the best examples of biological and geological features in...

 in 1966 because it contains the great ripples, (often measuring 25 to 50 feet high and 300 feet long), that served as a strong supporting element for J Harlen Bretz
J Harlen Bretz
J Harlen Bretz was an American geologist, best known for his research that led to the acceptance of the Missoula Floods, and also for his work on caves. He was born to Oliver Joseph Bretz and Rhoda Maria Howlett, farmers in Saranac, Michigan, as the oldest of five children...

's contention that Washington State's Channeled Scablands
Channeled scablands
The Channeled Scablands are a unique geological erosion feature in the U.S. state of Washington. They were created by the cataclysmic Missoula Floods that swept periodically across eastern Washington and down the Columbia River Plateau during the Pleistocene epoch. Geologist J Harlen Bretz coined...

 were formed by repeated cataclysmic floods over only about 2000 years, rather than through the millions of years of erosion that had been previously assumed.

The lake was the result of an ice dam
Ice dam
An ice dam occurs when water builds up behind a blockage of ice. Ice dams can occur in various ways.-Caused by a glacier:Sometimes a glacier flows down a valley to a confluence where the other branch carries an unfrozen river...

 on the Clark Fork
Clark Fork (river)
The Clark Fork is a river in the U.S. states of Montana and Idaho, approximately long. The largest river by volume in Montana, it drains an extensive region of the Rocky Mountains in western Montana and northern Idaho in the watershed of the Columbia River, flowing northwest through a long...

 caused by the southern encroachment of a finger of the Cordilleran Ice Sheet
Cordilleran Ice Sheet
The Cordilleran ice sheet was a major ice sheet that covered, during glacial periods of the Quaternary, a large area of North America. This included the following areas:*Western Montana*The Idaho Panhandle...

 into the Idaho Panhandle
Idaho Panhandle
The Idaho Panhandle is the northern region of the U.S. State of Idaho that encompasses the ten northernmost counties of Benewah, Bonner, Boundary, Clearwater, Idaho, Kootenai, Latah, Lewis, Nez Perce, Shoshone. Residents of the panhandle refer to the region as North Idaho...

 (at the present day location of Clark Fork, Idaho
Clark Fork, Idaho
Clark Fork is a city in Bonner County, Idaho, United States. The population was 536 at the 2010 census.-Geography:Clark Fork is located at ....

 at the east end of Lake Pend Oreille
Lake Pend Oreille
Lake Pend Oreille is a lake in the northern Idaho Panhandle, with a surface area of . It is 65 miles long, and 1,150 feet deep in some regions, making it the fifth deepest in the United States. It is fed by the Clark Fork River and the Pack River, and drains via the Pend Oreille River...

). The height of the ice dam typically approached 610 metres (2,001.3 ft), flooding the valleys of western Montana approximately 320 kilometres (198.8 mi) eastward. It was the largest ice-dammed lake known to have occurred.

The periodic rupturing of the ice dam resulted in the Missoula Floods
Missoula Floods
The Missoula Floods refer to the cataclysmic floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. The glacial flood events have been researched since the 1920s...

 – cataclysmic flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...

s that swept across Eastern Washington
Eastern Washington
Eastern Washington is the portion of the U.S. state of Washington east of the Cascade Range. The region contains the city of Spokane , the Tri-Cities, the Columbia River and the Grand Coulee Dam, the Hanford Nuclear Reservation and the fertile farmlands of the Yakima Valley and the...

 and down the Columbia River Gorge
Columbia River Gorge
The Columbia River Gorge is a canyon of the Columbia River in the Pacific Northwest of the United States. Up to deep, the canyon stretches for over as the river winds westward through the Cascade Range forming the boundary between the State of Washington to the north and Oregon to the south...

 approximately 40 times during a 2,000 year period. The cumulative effect of the floods was to excavate 210 cubic kilometres (50.4 cu mi) of loess
Loess
Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometre size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate...

, sediment and basalt from the channeled scablands
Channeled scablands
The Channeled Scablands are a unique geological erosion feature in the U.S. state of Washington. They were created by the cataclysmic Missoula Floods that swept periodically across eastern Washington and down the Columbia River Plateau during the Pleistocene epoch. Geologist J Harlen Bretz coined...

 of eastern Washington and to transport it downstream. These floods are noteworthy for producing canyon
Canyon
A canyon or gorge is a deep ravine between cliffs often carved from the landscape by a river. Rivers have a natural tendency to reach a baseline elevation, which is the same elevation as the body of water it will eventually drain into. This forms a canyon. Most canyons were formed by a process of...

s and other large geologic features through cataclysms
Catastrophism
Catastrophism is the theory that the Earth has been affected in the past by sudden, short-lived, violent events, possibly worldwide in scope. The dominant paradigm of modern geology is uniformitarianism , in which slow incremental changes, such as erosion, create the Earth's appearance...

 rather than through more typical gradual processes
Uniformitarianism
In the philosophy of naturalism, the uniformitarianism assumption is that the same natural laws and processes that operate in the universe now, have always operated in the universe in the past and apply everywhere in the universe. It has included the gradualistic concept that "the present is the...

.

See also


  • Missoula Floods
    Missoula Floods
    The Missoula Floods refer to the cataclysmic floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. The glacial flood events have been researched since the 1920s...

  • Glacial lake outburst flood
    Glacial lake outburst flood
    A glacial lake outburst flood is a type of outburst flood that occurs when the dam containing a glacial lake fails. The dam can consist of glacier ice or a terminal moraine...

  • Ice Age Floods National Geologic Trail
    Ice Age Floods National Geologic Trail
    The Ice Age Floods National Geologic Trail or Ice Age Floods Trail is designated as the first National Geologic Trail in the United States...

  • List of prehistoric lakes
  • Glacial Lake Agassiz
    Lake Agassiz
    Lake Agassiz was an immense glacial lake located in the center of North America. Fed by glacial runoff at the end of the last glacial period, its area was larger than all of the modern Great Lakes combined, and it held more water than contained by all lakes in the world today.-Conception:First...

  • Glacial Lake Ojibway
    Glacial Lake Ojibway
    Glacial Lake Ojibway was a prehistoric lake in what is now Northern Ontario and Quebec in Canada. Ojibway was the last of the great proglacial lakes of the last ice age. Comparable in size to Lake Agassiz , and north of the Great Lakes, it was at its greatest extent c. 8,500 years BP.Lake Ojibway...

  • Deluge (prehistoric)
    Deluge (prehistoric)
    In geomorphology, an outburst flood, which is a type of megaflood, is a high magnitude, low frequency catastrophic flood involving the sudden release of water. During the last deglaciation, numerous glacial lake outburst floods were caused by the collapse of either ice sheets or glaciers that...


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