A Study of the Nature and Incidence of Density Currents in a Shallow Glacial Lake

Abstract

Abstract This paper outlines the findings of a study of sedimentation processes in a shallow glacial lake in which an integrated, basinwide instrumentation network, a multidimensional underwater sensor array, and a central rapid scan data-recording system were employed to obtain detailed information on processes both in and around the lake. The results presented here focus upon the nature and occurrence of density currents in the lake over a two-season period. The general character of the system includes a largely isothermal lake environment, water residency times of only 8–12 days, and considerable sediment throughput with over 30 percent of the incoming sediment load moving through the system. The lack of significant thermal stratification and the tendency toward generally isopycnal conditions precludes a conventional over-, inter-, and underflow model of density currents. It appears instead that an over- and underflow model with homopycnal mixing is more appropriate. The overflows, largely wind driven, are frequent events, and on occasion wind-driven translake overflows occur. Underflows, occurring with density differences as low as 0.19 kg m-3, are also frequent and may reach velocities capable of eroding the finer materials. Core data support many of the findings from the instrumentation network. Finally, the results point to the need for careful measurement of both input and output variables and the significance of even small variations in the entrance conditions on sedimentation processes in the lake.