Erosion of Paleozoic bedrock in the terminal zone of Yoho Glacier, British Columbia

Kodybka, Richard Joseph (1981) Erosion of Paleozoic bedrock in the terminal zone of Yoho Glacier, British Columbia. Masters thesis, Memorial University of Newfoundland.

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Abstract

Recent research has revealed differing points of view as to whether the physical characteristics of glacial debris are determined by the lithology of eroded bedrock or are a function of the environment of transport and deposition. A gap exists in the literature concerning short distances of transportation where relatively soft sedimentary rocks predominate and the resultant eroded bedform morphologies. -- In the proglacial zone of Yoho Glacier, British Columbia, there are seven main sedimentary lithologies which have been exposed by recent, post-Neoglacial recession. The beds lie across the former direction of ice movement. Both erosional and depositional surfaces are exposed and virtually unmodified by other geomorphic and subaerial processes. It is therefore possible to compare the bedrock erosion and comminution processes for varying adjacent sedimentary bedrock types under the same general ice conditions. -- In order to gain an understanding of sub-glacial erosional processes from the examination of bedrock lithology, contents of related tills, and surface roughness, certain field and laboratory procedures were adopted and designed. In an attempt to combine glaciological and glacial-geological practices, certain procedures can be viewed as standard. Others have been adopted from the engineering and computer sciences disciplines to help demonstrate some physical and chemical characteristics of lithology, tills and surfaces (bedrock) that have in the past been given only passing examination. -- Laboratory analyses conducted on till samples did not produce results that enable definite conclusions to be drawn about the relationship between bedrock type and their volumetric abundance in till. Although bimodality is observed in the grain size distribution curves with apparent terminal grade modes, it is doubtful that these characteristics are solely the result of either bedrock type, distance of transport, or mode of transport, but rather a combination of these. The excavation of large boulders and their subsequent deposition down-valley from their source (1.5 km) clearly indicates that not all materials are greatly reduced in bulk. However, because bimodality is observed in all samples, the bedrock units were probably comminuted to some degree due to a combination of abrasion and plucking, in transport for up to 1.5 km from their source. -- To indicate the roughness of a given bedrock unit, the extent of each physical and chemical characteristic of the bedrock unit must be specified. It is hypothesized that 'ideal plane' or 'ideal sliding surface' configurations (surface roughness) of bedrock units need not necessarily be horizontally level to enhance glacier flow. Based on physical and chemical characteristics of bedrock types, and of glacier ice conditions at the ice-rock interface, each bedrock unit tends toward its own configuration which enhances flow and retards erosion. The roughness of a bedrock unit can be viewed as its morphological variation from its ideal plane or ideal sliding surface configuration which may not necessarily be a smooth surface (horizontally level). -- The results of bedrock unit strength tests (susceptibility to erosion by physical and chemical processes), and of the ranking of bedrock units with reference to slope frequency distribution, ideal plane configuration and degree of horizontal levelness clearly indicates that over a given time period, relatively weaker bedrock units will erode to a smoother surface than stronger bedrock units.

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