Glacial Ice-Contact Rings and Ridges

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Abstract
Ice-contact rings and ridges are minor landforms associated with end moraines, hummocky and transitional ground moraines, hummocky and pitted outwash plains, moraine-lake plateaus, moraine plateaus, former ice-walled and ice-floored valleys, and other glacial landforms. They were investigated in south-central Saskatchewan and are known to occur in the Canadian provinces of Saskatchewan, Alberta, and Manitoba and in the United States in northern Montana, North Dakota, Minnesota, Wisconsin, Illinois, and Indiana. They are conspicuous landforms on aerial photographs. They resemble rings that are several hundred feet to several miles in diameter and a few tens of feet in relief. The circular features appear as oval, crenulated, or irregular-shaped landforms that form rims on the margins of moraine-lake plateaus and moraine plateaus and irregular regions of hummocky ground moraine. Ice-contact ridges may appear as straight ridges a few hundred feet to several miles long or as irregular, sinuous, or anastomosing ridges and elongate, straight or sinuous ridges that resemble links in a chain. Several ridges may be parallel in certain parts and merge or branch into others. Most are sharp-crested and about 100 to 250 feet across at their base. Ice-contact rings and ridges are interpreted as the end product of wasting stagnant- or dead-ice masses of various sizes and may be used to determine the manner and history of ice retreat and the most probable origin of associated landforms and deposits. The rings and ridges may form in either glaciolacustrine, glaciofluvial, ablational, or superglacial environments, some by sloughing off of ablational and englacial debris from stagnant-ice blocks and others possibly in part or entirely by a subglacial ice-press mechanism, or a combination of the two. The nature, proposed mechanism, and environment of formation of diverse ice-contact rings and ridges are illustrated. These include ice-contact rings marginal to moraine-lake plateaus and moraine plateaus; ice-contact ridges marginal to partly buried subglacial melt-water channels where ice, till, and/or bedrock served as valley walls; ridges marginal to partly buried melt-water channels where stagnant-ice blocks persisted in melt-water channels after adjacent uplands were deglaciated; ridges marginal to open melt-water channels and outwash plains; ice-contact rings and ridges associated with valleys eroded in ice and largely floored by ice; and ice-contact ridges marginal to hummocky and transitional ground moraine and some lake basins. They have been mapped with washboard moraines, ridged end moraines, and contorted bedrock ridges. Their occurrences with these landforms do not require unique explanations, however.

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