DYNAMICS OF SEDIMENT-LADEN UNDERFLOWS PASSING OVER A SUBAQUEOUS SILL - GLACIER-FED PEYTO LAKE, ALBERTA, CANADA

The dynamic behaviour of sediment-laden underflows was examined in Pey to Lake, Alberta, Canada, which contains a midlake sill 7 m high. Sedi ment-laden underflows are driven by the downslope component of negativ e buoyant gravity multiplied by the current's thickness. Our measureme nts of wind, lake currents and water properties indicate that underflo ws pass over the sill due to the active storage of turbid suspension n ear the bottom in the deepest proximal region. Sill overflows occurred only when a hydrological threshold of the inflowing river was exceede d, causing quasicontinuous underflow and associated sedimentation in t he distal region of the lake basin.