Evidence for temporally varying "sticky spots" at the base of Trapridge Glacier, Yukon Territory, Canada

During the 1992 summer field season we installed arrays of "plough-meters" and water-pressure transducers beneath Trapridge Glacier, Yukon territory, Canada, to study hydromechanical coupling at the ice-bed interface. Diurnal signals recorded with two of these ploughmeters appear to correlate with fluctuations in subglacial water pressure. These diurnal variations can be explained by changes in basal resistance to sliding as mechanical conditions at the bed vary temporally in response to changes in the subglacial hydrological system. We propose that a lubricating water film, associated with high water pressures, promotes glacier sliding, whereas low pressures cause increased basal drag resulting in "sticky" areas. Using a theoretical model,we analyze the sliding motion of glacier ice over a flat surface having variable basal drag and show that a consistent explanation can be developed. Results from our model calculations provide strong support for the existence of time-varying sticky spots which are associated with fluctuations in subglacial water pressure.