Glacial Beaches

The recession of the ice-sheets was marked by a series of halts and occasional re-advances of the ice sheet. During periods of stand-still, beach ridges formed along the existing shores of glacial lakes. The beaches are long narrow ridges of sand and gravel, smoothly rounded, rising 10 to 20 feet above the surrounding land. In some places, gravel beaches were not formed, but the till surface of the lake bed was terraced by wave action.

Following the formation of the Herman beaches, the ice-sheet retreated, and erosion of the Lake Traverse outlet continued, but apparently was interrupted by periods of slow erosion. As result, a series of beaches formed around the lake, at successively lower levels. Tilting accompanying the dcrease in ice load, again caused branching of the beaches to the north. The next series of beaches were the NOrcross, the Tintah, and the Campbell, all deposited in the period when Lake Agassiz drained to the south. During this period, the depth of water over what is now the south end of lake winnipeg decreased from 650 to 350 feet.

Once the ice-sheets had retreated as far as the mouth of the Nelson River, and access to the open sea was available, a sudden drainage of the remaining part of Lake Agassiz probably occurred, leaving behind the ancestral forms of the 3 large Manitoba lakes: Winnipeg, Manitoba, and Winnipegosis. The only changes in the area of Lake Winnipeg since glacial times have been brought about by the gradual lowering through natural erosion of the NElson River outlet through a depth of about 20 feet.

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