Lake Great Falls was a prehistoric

proglacial lake In geology, a proglacial lake is a lake formed either by the damming action of a moraine during the retreat of a melting glacier, a glacial ice dam, or by meltwater trapped against an ice sheet due to isostatic depression of the crust around th ...

which existed in what is now central

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

in the United States between 15,000

BCE Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian calendar (and its predecessor, the Julian calendar), the world's most widely used calendar era. Common Era and Before the Common Era are alternatives to the or ...

and 11,000 BCE.Hill, Christopher L. and Valppu, Seppo H. "Geomorphic Relationships and Paleoenvironmental Context of Glaciers, Fluvial Deposits, and Glacial Lake Great Falls, Montana." ''Current Research in the Pleistocene.'' 14 (1997); Hill, Christopher L. "Pleistocene Lakes Along the Southwest Margin of the Laurentide Ice Sheet." ''Current Research in the Pleistocene.'' 17 (2000); Hill, Christopher L. and Feathers, James K. "Glacial Lake Great Falls and the Late-Wisconsin-Episode Laurentide Ice Margin." ''Current Research in the Pleistocene.'' 19 (2002)
Reynolds, Mitchell W. and Brandt, Theodore R. ''Geologic Map of the Canyon Ferry Dam 30' x 60' Quadrangle, West-Central Montana: U.S. Geological Survey Scientific Investigations Map 2860, scale 1:100,000.''
Scientific Investigations Map 2860. Washington, D.C.: U.S. Geologic Survey, 2005.
''XVI International Quaternary Association Congress.'' Stratigraphy and Geochronology Session. International Quaternary Association, Reno, 2003. Centered on the modern city of Great Falls, Montana, Glacial Lake Great Falls extended as far north as

Cut Bank, Montana Cut Bank is a city in and the county seat of Glacier County, Montana, United States, located just east of the "cut bank" (gorge) along Cut Bank Creek. The population was 3,056 at the 2020 census, The town began in 1891 with the arrival of the G ...

, and as far south as

Holter Lake Holter Dam is a hydroelectric straight gravity dam on the Missouri River about northeast of Helena, Montana, in the United States.''Upper Missouri River Reservoir Fisheries Management Plan, 2010-2019,'' Montana Department of Fish, Wildlife and ...

. At present-day Great Falls, the Glacial Lake Great Falls reached a depth of 600 feet (183 metres). Approximately 1.5 million years ago, the Missouri River, the

Yellowstone River The Yellowstone River is a tributary of the Missouri River, approximately long, in the Western United States. Considered the principal tributary of upper Missouri, via its own tributaries it drains an area with headwaters across the mountains a ...

and

Musselshell River The Musselshell River is a tributary of the Missouri River, long from its origins at the confluence of its North and South Forks near Martinsdale, Montana to its mouth on the Missouri River. It is located east of the Continental divide entir ...

all flowed northward into a terminal lake.Clawson, Roger and Shandera, Katherine A. ''Billings: The City and the People.'' Helena, Mont.: Farcountry Press, 1998. During the last glacial period, the

Laurentide The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glacial epochs, from 2.58 million years a ...

and Cordilleran ice sheets pushed these lakes and rivers southward.Montagne J.L. "Quaternary System, Wisconsin Glaciation." ''Geologic Atlas of the Rocky Mountain Region.'' Denver: Rocky Mountain Association of Geologists, 1972. Between 15,000

and 11,000 BCE, the Laurentide Ice Sheet blocked the Missouri River and created Glacial Lake Great Falls. About 13,000 BCE, as the glacier retreated, Glacial Lake Great Falls emptied catastrophically in a

glacial lake outburst flood A glacial lake outburst flood (GLOF) is a type of outburst flood caused by the failure of a dam containing a glacial lake. An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a j� ...

. The meltwater poured through the

Highwood Mountains The Highwood Mountains are an island range (sub-range of the Rockies entirely surrounded by prairie) which cover approximately 4,659 km² (1,799 sq mi) of the Central Montana Alkalic Province in north central Montana in the U.S. They are in ...

and eroded the hundred mile-long,

Shonkin Sag The Shonkin Sag is a prehistoric fluvioglacial landform located along the northern edge of the Highwood Mountains in the state of Montana in the United States. The Sag is a river channel formed by the Missouri River and glacial meltwater pouring ...

—one of the most famous prehistoric meltwater channels in the world.Axline, Jon and Bradshaw, Glenda Clay. ''Montana's Historical Highway Markers.'' Rev. ed. Helena, Mont.: Montana Historical Society, 2008. ; Bowman, Isaiah. "Forest Physiography: Physiography of the United States and Principles of Soils in Relation to Forestry." ''American Environmental Studies.'' Reprint ed. Charles Gregg, ed. New York: Arno Press, 1970. Glacial lakes in Montana

Bibliography

*Alden, W. C., 1958, Physiography And Glacial Geology Of Eastern Montana And Adjacent Areas, U. S. Geological Survey Professional Paper 174. *Colton, R. B., Lemke, R. W., and Lindvall, R. M., 1961, Glacial map of Montana East of the Rocky Mountains, U. S. Geological Survey Miscellaneous Geological Investigations Map I-327. *Lindvall, R. M., 1962, Geology Of The Eagle Buttes Quadrangle, Chouteau County, Montana, U. S. Geological Survey Miscellaneous Geological Investigations Map I-349. *Thornbury, W. D., 1965, Regional Geomorphology Of The United States, John Wiley & Sons, Inc., New York.

References

{{DEFAULTSORT:Great Falls, Lake Former lakes of the United States Geology of Montana Glacial lakes of the United States Natural history of Montana Proglacial lakes Great Falls, Montana

Bibliography

See also

References