Cascading of water down the sloping sides of a deep lake in winter

During winter, the temperature of the water overlying the shallow, typicall y 2-5 m deep,'shelf' region around the edge of the 310 m deep Lake Geneva f alls more rapidly than that over deeper areas. This causes the spilling or 'cascading' of relatively dense water from the shallows down the sloping si des of the lake in the form of gravity currents, 2 - 15 m thick and typical ly 0.1 degreesC cooler than the ambient. The flow is intermittent with 'slu gs' of cold water lasting, on average, for 8 hrs with mean downslope speeds of 5.2 cms(-1) The temperature and thickness of the slugs is however varia ble, with pulses of colder water lasting for 1-3 hrs, each preceded by a 'f ront' in which thickness increases and temperature falls by about 0.01 degr eesC per min. The net volume flux carried by the 'slugs' is 18.5 times the mean winter flow into the lake from rivers.