"Subglacial Drainage is now recognised as one of the most important branches of Glaciology". Evaluate This Statement.

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Rob Anders        Tutorial Assignment 4 – Glacial Environments        December 2003

"Subglacial Drainage is now recognised as one of the most important branches of Glaciology". Evaluate This Statement.

“The hydrological component of glacial systems is of great significance to the description and flow regime of glaciers” (Iken, 1981) in turn relating to many human interests. Water supplies in Central Asia and the Canadian highlands depend upon glacial drainage for much of the year for irrigation purposes. In Alpine glaciated regions such as the Swiss and French Alps and Norway, relying on such concentrated water systems is essential for hydroelectric power. Knowledge of glacial drainage also seems essential to calculate sudden drainage events or outburst floods from ice dams, which have threatened areas of Peru, Iceland and Alaska for centuries.

Sub glacial drainage also influences basal flow, which feeds back to manipulate glacier motion and therefore provides feasible explanations for flow dynamics and surge events. It is this subglacial component of glacial water that provides the hub for this paper; specifically the importance of sub glacial drainage with respect to glacier motion. Subglacial drainage will also be looked at from its two fundamental distinctions; ‘discrete’ and ‘distributed’. In the former, water is confined to a few channels or conduits, whereas distributed systems transport water over the whole of, or a large proportion of the bed.

Subglacial water was first considered to form a film or sheet at the sole of the glacier (Weertman, 1972). Water was thought to cover around 80% of the bed, originating from basal melt rather than surface percolation. Weertman described a thin film which formed on bedrock irregularities through the process of regelation. This formed the basis of his theory of glacial sliding. Nevertheless, this was soon considered an over-simplified synopsis of subglacial processes, and was followed by theories of channelised flow.

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Discrete drainage systems are “efficient transporters of meltwater, allowing rapid flow through well connected channel systems” (Benn and Evans 1998). In contrast, distributed systems are “inefficient, and meltwater follows more tortuous routes through poorly connected networks” (Benn and Evans 1998). Therefore the type of drainage has important implications for glacier motion, by controlling water pressure condition at the bed.

A study of discrete subglacial channels was conducted by Seaburg et al. (1988) using dye tracing at Storglaciaren, Sweden.  Dye was poured into a ‘Moulin’ in the lower part of the ablation area in the glacier, and the time for the ...

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