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The Quaternary Landscape of Manitoba
South of 53°
Eastward-facing bedrock escarpments culminating in cuestas which form the Manitoba Escarpment provide a foundation for the present-day landscape of southern Manitoba. To the east, the landscape is dominated by Precambrian rocks and bedrock structure, such as faulting, is commonly visible.
Above the Manitoba Escarpment, the landscape is dominated by hummocky moraine or dead-ice topography, streamlined topography and glacial spillways. Many areas are covered by thick sequences of glacial till representing numerous glacial episodes dating back more than 100,000 years. The most recent glacial advances were from the northwest. Glacial till tends to be clay rich.
The Interlake is dominated by streamlined landforms and in lower areas, glaciolacustrine depositional basins. Quaternary sediments tend to be relatively thin and the preservation of older sediments is uncommon, limited to bedrock protected areas such as escarpments. Bedrock outcrops are common. Glacial advance was generally from the northwest, parallel to the streamlined landforms. Glacial till is typically silt rich. Glacial retreat occurred in a series of steps marked by moraines: the Darlingford Moraine (~11,000 years old); the Sandilands Moraine, which represents the interlobate position of the Rainy lobe from the northeast and the Red River lobe from the northwest; the Birds Hill–Belair Moraine; the Teulon Moraine; and The Pas Moraine (~9000 years old). George Island Moraine, contemporaneous with and to the east of The Pas Moraine, is another ice margin of the retreating Rainy lobe.
North of 53°
In the Precambrian shield, rock outcrops dominate the landscape. Quaternary sediments are commonly thick, but discontinuous, rarely completely infilling the bedrock lows. Older sediments, including saprolites, are often preserved in the bedrock lows where they are protected from glacial erosion. Glacial advance was generally from the northeast. Glacial till is typically sand rich.
As the glaciers retreated, glacial lakes Souris and Hind formed and drained, and glacial Lake Agassiz expanded northward, progressively covering the entire area below the Manitoba Escarpment. Major Lake Agassiz landforms include the Assiniboine Delta, which formed as glacial meltwater flowed from the Assiniboine spillway, and clay plains composed of tens of metres of clay and silt. The Herman beaches indicate the highest level attained by Lake Agassiz in southern Manitoba. The Upper Campbell beach is the best developed of the Lake Agassiz beaches and is evident along the base of the Manitoba Escarpment.
Holocene modifications to the landscape include eolian activity (sand dunes) primarily in the Assiniboine Delta and the Sandilands Moraine; the Portage la Prairie alluvial fan, from which fluctuating Assiniboine River flow directions over the last 7000 years have been documented; smaller alluvial fans that have developed along the Manitoba Escarpment; large landslide areas (colluvium) that are active along the northern part of the Manitoba Escarpment; and organic accumulations (bogs and fens) with basal radiocarbon dates of approximately 6000 years, that occur in the northeast and extend westward into the northern and eastern Interlake and southward into southeastern Manitoba.
