FLOW DYNAMICS OF A POLYTHERMAL GLACIER, STAGNATION GLACIER, BYLOT ISLAND, NUNAVUT, CANADA
WILLIAMS, JEFFREY L.M.. University of Calgary.
Walter, Frederic S.A.. University of Calgary.
Moorman, Brian J.. University of Calgary.
From July 12 - July 21, 2001, a detailed survey was conducted on a section of the ablation area on Glacier B28, informally named Stagnation Glacier on Bylot Island, Nunavut, Canada. The objective of the study was to quantify surface movement of an Arctic polythermal glacier. Observations included measurements of surface movement in both vertical and horizontal directions. The study was based on the assumption that meltwater, trapped within the glacier, would cause surface uplift, as had been previously observed on the glacier.
Polythermal glaciers are dominated by a strong vertical temperature gradient in the ablation zone, while near the centre line, a thick covering of cold ice surrounds temperate ice that extends to the glacier bed. Glacier movement in polythermal glaciers tends to increase during the summer over the entire ablation area, and may persist after the end of the melt season. Researchers suggest that high water pressures and sliding above the lowest points of surface-water input may initiate the trapping of meltwater by the marginal zone of thin ice that is frozen to the bed, thus forcing meltwater up-glacier.
Researchers observed turbid englacial water exiting the eastern and western margins of White Glacier, but not from the glacier snout, suggesting that a barrier of cold ice was preventing the drainage of meltwater to the snout (Skidmore 1995). If, however, the basal hydraulic gradient is down glacier, meltwater will flow towards the snout and unable to penetrate the cold ice barrier, begins to pool. If the meltwater input is significantly larger than the meltwater output, then water storage will occur until a critical point is reached and bed separation occurs.
Glacier motion, on a daily to weekly temporal scale is characterized by; (a) correlation between surface water inputs and glacier motion, (b) time lag between surface water inputs and glacier motion, and (c) varying medium-term velocity increases with distance up glacier (Willis 1995). Studies suggest that daily - weekly variations in glacier surface velocity are positively correlated with meltwater inputs derived from surface melt or rainfall (Willis 1995). Daily - weekly increases in glacier surface uplift have currently only been reported for the Unteraargletscher Glacier in Switzerland. Peak daily - weekly horizontal velocities were associated by three uplift events which resulted in the surface rising 0.51 m, 0.49 m and 0.53 m above the normal flow curve (Iken et al. 1983).
Previous radar studies have suggested that Stagnation Glacier is dominated by a transition of cold ice around the margins of the glacier and a core at the pressure melting point (Moorman and Michel 2000). Based on this assertion it is suggested that Stagnation Glacier is a polythermal glacier, thus resulting in the glacier being dominated by marginal streams and not by glacial streams exiting the terminus.
A detailed array of markers were surveyed using theodolite total station measurements of surface movement to observe horizontal and vertical displacement of a section of Stagnation Glacier. Weather data was collected from a weather station located within the adjacent valley and discharge, conductivity and pH of the proglacial stream were monitored for the extent of the field season. While preliminary results fail to reveal vertical uplift of the glacier surface, a surface lowering of ca. 1.70 mm/h, potentially caused by ablation, was observed. Horizontal measurements revealed surface velocities of ca. 4-5 mm/h with peak velocities not corresponding to peaks in discharge. Dye-tracing tests revealed that the drainage system evacuating Stagnation Glacier was dominated by rapid through flow which does not permit water storage to occur. Future research will determine overall flow patterns of the glacier ice on the surface and internally and conclude whether ablation is the principal factor affecting surface lowering.
Iken, A., Rothlisberger, H., Flotron, A. and Haeberli, W., 1983, The uplift of Unteraargletscher at the beginning of the melt season - A consequence of water storage at the bed?: Journal of Glaciology, vol. 29, p. 28-47.
Moorman, B.J. and Michel, F.A., 2000, Glacial hydrological system characterization using ground-penetrating radar: Hydrological Processes, v.14, p. 2645-2667.
Skidmore, M. L., 1995, The hydrology and hydrochemistry of a high Arctic glacier: Unpublished Master of Science Thesis, Unviersity of Alberta.
Willis, I. C., 1995, Intra-annual variations in glacier motion: a review: Progress in Physical Geography, v. 19, p. 61-106.
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