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.
First postulated in 1823 by William Keating, it was named by Warren Upham in 1879 after Louis Agassiz, after he (Upham) recognized it was formed by glacial action.
Geologists have come to a consensus on the likely geological history of Lake Agassiz.
During the last Ice Age, northern North America was covered by a glacier, which alternately advanced and deteriorated with variations in the climate. This continental ice sheet formed during the period now known as the Wisconsin glaciation, and covered much of central North America between 30,000 and 10,000 years ago. As the ice sheet disintegrated, it created at its front an immense proglacial lake, formed from its meltwaters.
Around 13,000 years BP the lake came to cover much of Manitoba, western Ontario, northern Minnesota, eastern North Dakota, and Saskatchewan. At its greatest extent, it may have covered as much as 440,000 square kilometers, larger than any currently existing lake in the world (including the Caspian Sea).
The lake drained at various times south through the Traverse Gap into Glacial River Warren (parent to the Minnesota River, a tributary of the Mississippi River), east through Lake Kelvin (modern Lake Nipigon) to what is now Lake Superior, or west via the Mackenzie River through the Northwest Territories. Geologists believe that a major outbreak of Lake Agassiz about 13,000BP drained north through the Mackenzie River into the Arctic Ocean. A return of the ice for some time offered a reprieve, but after retreating north of the Canadian border about 9,900 years ago, Lake Agassiz refilled. The last major shift in drainage occurred about 8,400 years BP. The melting of remaining Hudson Bay ice caused lake Agassiz to drain nearly completely. This final drainage of Lake Agassiz contributed an estimated 1 to 3 meters to total post-glacial global sea level rise. Much of the final drainage may have occurred in a very short time, in two or one events, perhaps taking as little as a year.
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