LAURENTIDE GLACIAL LANDSCAPES - THE ROLE OF ICE STREAMS

Glacial landforms of the North American prairie can be divided into tw o Suites that result from different styles of ice flow: (1) a lowland suite of level-to-streamlined till consistent with formation beneath i ce streams, and (2) an upland and lobe-margin suite of thick, hummocky till and glacial thrust blocks consistent with formation at ice-strea m and ice-lobe margins. Southern Laurentide ice lobes hypothetically f unctioned as outlets of ice streams. Broad branching lowlands bounded by escarpments mark the stable positions of the ice streams that fed t he lobes, If the lobes and ice streams were similar to modern ice stre ams, their fast flow was facilitated by high subglacial water pressure . Favorable geology and topography in the midcontinent encouraged nonu niform ice flow and controlled the location of ice streams and outlet lobes.