Water from the melting glacier could have been trapped between ice bodies before draining off the landscape. These ice-walled lakes may have existed for decades and collected sediments from the melting glacier. After the ice walls completely melted, the profile of the former lake bottom appears as an large elevated area or mound with a distinct oval or circular surface shape. Rock debris moved by glaciers was deposited as large ridges or piles near it's terminus as the ice melted. Their numerous locations indicate a complex series of ice advances and retreats during the glaciation period.
Moraines are hummocky , hilly , and can be steep .
They are often seen as prominent ridges along the horizon out from which large boulders have weathered . The large Bemis moraine oriented in a northwest-southeast direction near Sisseton has a vertical relief of 250m in some places relative to the Minnesota River valley to the east. It marks the western position of the Des Moines ice lobe and the prairie coteau. Before vegetation was established on the exposed till after the glacier melted, it was subjected to significant wind erosion. Loess also occurs as a thin mantle over some glacial till and forms very productive soils.