Glacial Lake Grantsburg

The proglacial lakes of Minnesota were lakes created in what is now the U.S. state of Minnesota in central North America 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 moraines left by the glaciers. Evidence for these lakes is provided by low relief topography and glaciolacustrine 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, 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 was an enormous lake, larger in area than all the Great Lakes combined, and the largest body of fresh water ever to have existed in North America. It extended from its outlet near Browns Valley, Minnesota west into South Dakota and North Dakota and north into Saskatchewan, Manitoba, and Ontario. In Minnesota the lake occupied the Red River Valley in northwestern Minnesota and the western part of the watershed of the Rainy River in the northern part of the state. Its southern outlet was through the Traverse Gap, a spillway channel cut through the Big Stone Moraine by Glacial River Warren, an enormous stream which carved the valley of the Minnesota River as well as that of the Upper Mississippi River below the confluence of those successor streams. Lake Agassiz' present-day remnants include Lake of the Woods and Upper and Lower Red Lake.

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