Northern North America was covered during the…

Northern North America was covered during the last Ice Age by a glacier that alternately advanced and deteriorated with variations in the climate.

Lake Agassiz came to cover much of Manitoba, western Ontario, northern Minnesota, eastern North Dakota, and Saskatchewan around 13,000 years BP, when the continental ice sheet formed during the period now known as the Wisconsin glaciation, and covering much of central North America between thirty thousand and ten thousand years ago, created at its disintegrating front an immense proglacial lake, formed from its meltwaters.

At its greatest extent, it may have covered as much as four hundred and forty thousand 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 13,000 BP 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.

Lake Agassiz' major drainage reorganization events were of such magnitudes that they had significant impact on climate, sea level and possibly early human civilization.

Major freshwater release into the Arctic Ocean is considered to disrupt oceanic circulation and cause temporary cooling.

The draining at 13,000 BP may be the cause of the Younger Dryas stadial.

The draining at 8400 may be the cause of the 8.2-kiloyear event.

A recent study by Turney and Brown links the 8400 drainage to the expansion of agriculture from east to west across Europe; he suggests that this may also account for various flood myths of prehistoric cultures, including the Biblical flood.

Lake Winnipeg, Lake Winnipegosis, Lake Manitoba, and Lake of the Woods, among others, are relics of the ancient lake.

The outlines and volumes of these modern lakes are still slowly changing due to differential isostatic rebound.