The proglacial lakes of Minnesota were lakes created in what is now the

U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its so ...

Minnesota Minnesota ( ) is a U.S. state, state in the Upper Midwestern region of the United States. It is bordered by the Canadian provinces of Manitoba and Ontario to the north and east and by the U.S. states of Wisconsin to the east, Iowa to the so ...

in central

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

in the waning years of the last glacial period. As the Laurentide Ice Sheet decayed at the end of the Wisconsin glaciation, lakes were created in depressions or behind

moraine A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...

s left by the glaciers. Evidence for these lakes is provided by low relief topography and

glaciolacustrine Sediments deposited into lakes that have come from glaciers are called glaciolacustrine deposits. In some European geological traditions, the term limnoglacial is used. These lakes include ice margin lakes or other types formed from glacial erosio ...

sedimentary deposits. Not all contemporaneous, these glacial lakes drained after the retreat of the lobes of the ice sheets that blocked their outlets, or whose meltwaters fed them. There were a number of large lakes, one of which,

Glacial Lake Agassiz Lake Agassiz ( ) was a large proglacial lake that existed in central North America during the late Pleistocene, fed by meltwater from the retreating Laurentide Ice Sheet at the end of the last glacial period. At its peak, the lake's area was ...

, was the largest body of freshwater known to have existed on the North American continent; there were also dozens of smaller and more transitory lakes filled from glacial meltwater, which shrank or dried as the ice sheet retreated north.

Glacial Lake Agassiz

Glacial Lake Agassiz was an enormous lake, larger in area than all the

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, H ...

combined, and the largest body of fresh water ever to have existed in North America.Waters, ''Streams and Rivers of Minnesota'', p. 106. It extended from its outlet near

Browns Valley, Minnesota Browns Valley is a city in Traverse County, Minnesota, United States, adjacent to the South Dakota border. The population was 558 at the 2020 census. Browns Valley lies along the Little Minnesota River between the northern end of Big Stone ...

west into

South Dakota South Dakota (; Sioux language, Sioux: , ) is a U.S. state, state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Dakota people, Dakota Sioux ...

and

North Dakota North Dakota ( ) is a U.S. state in the Upper Midwest, named after the indigenous Dakota people, Dakota and Sioux peoples. It is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minneso ...

and north into

Saskatchewan Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...

Manitoba Manitoba is a Provinces and territories of Canada, province of Canada at the Centre of Canada, longitudinal centre of the country. It is Canada's Population of Canada by province and territory, fifth-most populous province, with a population ...

, and

Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...

. In Minnesota the lake occupied the

Red River Valley The Red River Valley is a region in central North America that is drained by the Red River of the North; it is part of both Canada and the United States. Forming the border between Minnesota and North Dakota when these territories were admitted ...

in northwestern Minnesota and the western part of the

watershed Watershed may refer to: Hydrology * Drainage divide, the line that separates neighbouring drainage basins * Drainage basin, an area of land where surface water converges (North American usage) Music * Watershed Music Festival, an annual country ...

of the Rainy River in the northern part of the state. Its southern outlet was through the

Traverse Gap The Traverse Gap is an ancient river channel occupied by Lake Traverse, Big Stone Lake, and the valley connecting them at Browns Valley, Minnesota. It is on the border of the U.S. states of Minnesota and South Dakota. Traverse Gap has an unusual ...

, a spillway channel cut through the Big Stone Moraine by

Glacial River Warren Glacial River Warren, also known as River Warren, was a prehistoric river that drained Lake Agassiz in central North America between about 13,500 and 10,650 BP calibrated (11,700 and 9,400 14C uncalibrated) years ago. A part of the uppermost porti ...

, an enormous stream which carved the valley of the

Minnesota River The Minnesota River () is a tributary of the Mississippi River, approximately 332 miles (534 km) long, in the U.S. state of Minnesota. It drains a watershed of in Minnesota and about in South Dakota and Iowa. It rises in southwestern ...

as well as that of the

Upper Mississippi River The Upper Mississippi River is the portion of the Mississippi River upstream of St. Louis, Missouri, United States, a city at the confluence of its main tributary, the Missouri River. Historically, it may refer to the area above the Arkansa ...

below the confluence of those successor streams. Lake Agassiz' present-day remnants include

Lake of the Woods Lake of the Woods (; ) is a lake occupying parts of the Canadian provinces of Ontario and Manitoba and the U.S. state of Minnesota. Lake of the Woods is over long and wide, containing more than 14,552 islands and of shoreline. It is fed by t ...

and Upper and Lower Red Lake.

Glacial Lake Upham

Glacial Lake Upham was formed in the wake of the retreat of the St. Louis Sublobe of the Des Moines Lobe.Ojakangas and Matsch, ''Minnesota's Geology'', p. 109. It drained through a series of successively lower outlets to Glacial Lake Duluth. Its former lake bed is now a broad boggy area comprising much of the watershed of the latter stream.

Glacial Lake Aitkin

Glacial Lake Aitkin was also a product of the recession of the St. Louis Sublobe, and for significant portions of its history was contiguous with Glacial Lake Upham. It occupied a broad lowland along the valley of the present-day Mississippi River between

Grand Rapids Grand Rapids is the largest city and county seat of Kent County, Michigan, United States. With a population of 198,917 at the 2020 United States census, 2020 census and estimated at 200,117 in 2024, Grand Rapids is the List of municipalities ...

and Aitkin in north central Minnesota. The lake bed is now a sandy and clayey plain. It is also a source for reed-sedge

peat Peat is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. ''Sphagnum'' moss, also called peat moss, is one of the most ...

, which is harvested, processed, and packaged for agricultural applications; it enables plants to fix nitrogen and thereby reduces the need for fertilizer. The company harvesting the peat and the University of Minnesota-Duluth are developing processes to use the peat to extract mercury and other heavy metals, and also to remove sulfates from water by a method which enables the peat to be reused.

Glacial Lake Duluth

Glacial Lake Duluth is the name given to the largest of a series of named lakes or lake stages occupying parts of the western

Lake Superior Lake Superior is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. Lake Michigan–Huron has a larger combined surface area than Superior, but is normally considered tw ...

basin. The name derives after a prominent terrace in the city of Duluth, along which Skyline Parkway was built, that was created by

coastal erosion Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of Wind wave, waves, Ocean current, currents, tides, wind-driven water, waterborne ice, or other impacts ...

in Glacial Lake Duluth. As lower elevation outlets to the east was blocked by the Superior Lobe of the ice sheet, Lake Duluth drained through two outlets which crossed the present

Laurentian Divide The Laurentian Divide also called the Northern Divide and locally the '' height of land'', is a continental divide in central North America that separates the Hudson Bay watershed to the north from the Gulf of Mexico watershed to the south and ...

to the valleys of the Saint Croix River and the

Mississippi Mississippi ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South regions of the United States. It borders Tennessee to the north, Alabama to the east, the Gulf of Mexico to the south, Louisiana to the s ...

. One outlet was a route from the western part of the lake through the

Nemadji River The Nemadji River is a river rising in Pine County, Minnesota, United States, which flows through Carlton County, Minnesota, and Douglas County, Wisconsin, to Lake Superior. The river is long measured from its source in Maheu Lake in Pine Coun ...

basin and down the present

Moose The moose (: 'moose'; used in North America) or elk (: 'elk' or 'elks'; used in Eurasia) (''Alces alces'') is the world's tallest, largest and heaviest extant species of deer and the only species in the genus ''Alces''. It is also the tal ...

and Kettle Rivers; the other was via the modern Bois Brule River to the Saint Croix. Glacial Lake Duluth's highest level was around 1060' in the city of Duluth, but rises as high as 1350' near the border with Ontario. When the glacier retreated the lake was able to drain to the east to the Lake Michigan basin via outlets across the upper Peninsula of Michigan.

Glacial Lake Grantsburg

Glacial Lake Grantsburg formed when the Grantsburg Sublobe of the Des Moines Lobe blocked southward drainage of the ice-free land to its north. It extended from St. Cloud east-northeast to

Grantsburg, Wisconsin Grantsburg is a village in Burnett County, Wisconsin, Burnett County, Wisconsin, United States. The population was 1,341 at the 2010 United States Census, 2010 census. The village is located within the Grantsburg, Burnett County, Wisconsin, Tow ...

, whence its outflow ran south along the east

front Front may refer to: Arts, entertainment, and media Films * ''The Front'' (1943 film), a 1943 Soviet drama film * '' The Front'', 1976 film Music * The Front (band), an American rock band signed to Columbia Records and active in the 1980s and ...

of the ice sheet down the valley of the Saint Croix River.

Glacial Lake Minnesota

Glacial Lake Minnesota was a complex of lakes formed by or on the Des Moines Lobe generally south of

Mankato, Minnesota Mankato ( ) is a city in Blue Earth County, Minnesota, Blue Earth, Nicollet County, Minnesota, Nicollet, and Le Sueur County, Minnesota, Le Sueur counties in the U.S. state of Minnesota. It is the county seat of Blue Earth County, Minnesota. The ...

. Evidence for it is found in

lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

sediments in that region. The lakes may have consisted of bodies of water trapped on the surface of the decaying ice sheet, lakes created as the lobe retreated, or depressions filled from the overflow of Glacial River Warren.Hudak and Hajic
''Landscape Suitability Models for Geologically Buried Precontact Cultural Resources''
, section 12.3.4.1 (''Landscapes: Paleo-Valley Landscape'').

References

Notes

Sources

* * * * * * * * {{Pleistocene Lakes and Seas Geology of Minnesota Paleogeography Proglacial lakes