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Glacial Deposition

Glacial deposition occurs during glaciation. It refers to the various means by which materials carried by a glacier can be released from the ice and deposited on underlying surfaces or in surrounding areas. Glacial deposition can occur directly from the glacier itself or from several associated processes involving glacial meltwater. Saskatchewan has evidence of glacial deposition throughout the province, although deposits south of the Precambrian Shield tend to be thicker and more continuous. Glaciers can erode, transport and deposit materials that range in size from the finest clay particles to blocks of rock hundreds of metres in size. Thus there is a wide range of glacial depositional landforms in the province, the most prominent of which include eskers, former lake beds, deltas, and various types of moraines from ridged to flat to hummocky plains.

Material deposited directly from glacial ice is called glacial till. Till typically has undergone little or no sorting by meltwater, so the resulting deposit is poorly sorted and contains a wide range of particle sizes, from grains of clay to boulders, jumbled together. Till forms the basis of many Saskatchewan landforms and can develop with ice advance and retreat, and in periods of stagnation. Till plains develop from materials deposited directly from the ice with the steady retreat of the glacier, while rolling landscapes called hummocky moraines are thought to form during ice stagnation. Recessional moraines, which appear as ridges of thicker deposits, developed along the ice margin during periods of glacial standstill. Erratics appear as isolated boulders or chunks of bedrock deposited directly from glacial ice often hundreds of kilometres away from their origin. Saskatchewan has several spectacular examples of erratics, such as that near Young, which is composed of rocks from the northern area.

Sediments can be deposited through the medium of glacial meltwater. In Saskatchewan these processes primarily relate to glacial meltwater stream and glacial lake deposits, referred to in the literature as glaciofluvial and glaciolacustrine deposits respectively (see Proglacial Lakes). In this case, deposits from the glacier can be built up hundreds of kilometres from the actual glacier margin. Deposits from meltwater streams or in proglacial lakes tend to be sorted into layers with respect to the grain size of the particle: thus discrete layers of sands, silts and clays may be observed. These sorted deposits are often highly valued in the aggregate industry. Other glacial deposits include eskers, which were former channel beds of meltwater streams that formed inside or at the base of a glacier. When the glacial ice melted, the stream channel was deposited on the underlying surface, appearing as a ridge on the landscape. Deltas formed at the end of these streams when they entered proglacial lakes.

Janis Dale

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Further Reading

Christiansen, E.A. 1979. “The Wisconsinan Deglaciation of Southern Saskatchewan and Adjacent Areas,” Canadian Journal of Earth Sciences 116: 913-38; Sugden, D.E. and B.S. John. 1976. Glaciers and Landscape. London: Edward Arnold.
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