CGRG Bibliography of Canadian Geomorphology
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Author : Brennand, T.; Sjogren, D.; and Burke, M.J.
Date : 2011.
Title : What controlled the distribution of Laurentide eskers?
Publication : American Geophysical Union (AGU) Fall Meeting 2011. December 5-9, 2011. San Francisco, California. USA.
Issue : C11E-0718.
Page(s) :
Abstract
Eskers are the casts of ice-walled tunnels and are a common landform within the footprint of the last Laurentide Ice Sheet (LIS). Over crystalline bedrock eskers are relatively long and ubiquitous; they are shorter and less common over sedimentary bedrock. Assuming that glaciers overriding sedimentary bedrock necessarily produce deforming beds, this distribution has been attributed to the preferential development of canals over soft beds, and R-channels over rigid substrates. However, over the western Canadian sedimentary basin eskers are present over Mesozoic clastics and rare over Paleozoic carbonates. Thus, bed permeability rather than deformability has been implicated as the control on ice tunnel location there. More locally, in southern Alberta, the role of substrate permeability in determining R-channel location is ambiguous: eskers preferentially occur over thick till yet not over bedrock aquitards. Substrate controls on plumbing style aside, eskers also require an adequate water and sediment supply to form. Eskers are rare or small in driftless areas of the Canadian Shield and in clast-poor drift areas of southern Alberta. These observations highlight the importance of sediment supply on esker distribution. Inspection of current LIS reconstructions reveals that the majority of Laurentide eskers formed ~11.5-7 cal. ka BP, a time of rapid temperature increase and melting. Under such conditions the LIS would have developed numerous melt ponds on its surface, much like the Greenland Ice Sheet (GrIS) today. Drainage of many of these melt ponds to the bed, and sediment entrainment and transport in ice tunnels at the bed favoured the post-Younger Dryas production of a dense esker network. Consequently, we suggest that the dominant controls on LIS esker distribution are sediment supply and climate (water supply), and that eskers may be forming today under the GrIS in association with melt pond drainage.
Bibliography of Canadian Geomorphology