ABSTRACT: Dynamic sedimentation processes in a glacier-fed lake, Peyto Lake, Alberta, Canada

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Abstract

Physical sedimentation in glacier-fed Peyto Lake, Alberta was examined for the ice melting period of 1987, by measuring lake currents, suspended sediment concentration and water temperature. During the observation period of June-August, the heavy sediment discharge of an inflow river, Peyto Creek, continuously induced sediment plumes in a surface layer of the lake and turbidity currents in the bottom layer. Their offshore conservative behaviors are basically due to the slow settling of input fine sediment (silt and clay > 70 wt %). The bottom water, which has a both a high velocity and sediment concentration, was longitudinally observed as the bottom currents flowed from near the inflow river mouth to the outflow river mouth. Noting a difference in the driving force of bottom sedimentary flows, the results may be explained by: (1) 'turbidity currents,' driven by the downslope gravity force, flowed down to the deepest region of the southern sub-basin, bounded by a subaqueous sill in the central part of the lake; (2) 'bottom suspension flows,' probably induced by strong wind driven currents, subsequently flowed on the upslope of the sill, while suspending the sediment transported by the turbidity currents, and consequently passing over the sill; and (3) turbidity currents weakened by sediment deposition flowed on the downslope toward the deepest region of the distal northern sub-basin. The possibility that wind driven currents act as a driving force for suspension flow is supported by the specific spatial distribution of the sedimentation rate for sediments trapped near the bottom. The shear force of turbidity currents and suspension flows is numerically determined by applying the drag law at boundaries. The depositional and erosional conditions of suspended and bottom sediments, transported by the two sedimentary flows, can then be examined by using the 'extended Shields diagram' in which an experimental result of sediment deposition is considered.

Bibliography of Canadian Geomorphology