The record of density-induced underflows in a glacial lake



As part of an overall study of sedimentation processes in a proglacial lake an effort was made to compare field results with some of the general equations for density flows. The results suggest that in relatively small glacial lakes the occurrence of underflows with lower sediment loads involves a complex interplay between thermal and sediment effects which is extremely sensitive to varying hydrologic and climatic conditions. In terms of actual transport mechanics the results: (i) indicate that a higher α value of 0·6 or 0·7 gives a closer agreement between the measured velocity values and the established equations on moderately shallow slopes; (ii) provide field support for the experimentally derived relationship of Britter & Linden (1980) for the velocity of underflows and suggest the equation may be applicable in situations below 5° slopes; and (iii) support the relationship between velocity of the front and body of a continuous underflow for moderate slope situations suggested by Middleton (1966b). Finally the velocity values measured by electromagnetic current meters stationed in the lake, the grain-size data obtained from mapping core data, and the application of other criteria support the concept that in this environment the underflows are capable of erosion.