Ice-Disintegration Features in Western Canada

The wasting Wisconsin glacier left predominantly till deposits in western Canada and only subordinate amounts of stratified drift. In the final phases of wasting, the ice separated in places into a large number of small, dead, ice blocks: it disintegrated. This disintegration caused the preservation of many different land forms, some of which were initiated during the time of ice flow, others originated after flow ceased. Those features that show the influence of the previous live ice are said to be "controlled." Such control may be exerted by crevasses and thrust planes which are the response to stresses operative in a living glacier. Uncontrolled deposits do not reveal the influence of former flow. All gradations between controlled and uncontrolled disintegration can be observed. The depositional disintegration features include hummocks, moraine plateaus, round and irregularly shaped closed ridges, linear ridges, and washboard moraines. Ice-walled channels are an erosional form. The hummocky terrain and the closed ridges are regarded as the dominant product of uncontrolled disintegration. The linear and washboard ridges developed along inherited lines of weakness in the disintegrating ice and are regarded as controlled disintegration features. Both uncontrolled and contolled deposits resulted from the sloughing of ablation material into cracks and cavities in the ice and from the squeezing of till upward into openings at the base of the ice.