THE GLACILACUSTRINE SEDIMENTARY ENVIRONMENT OF BOWSER LAKE IN THE NORTHERN COAST MOUNTAINS OF BRITISH-COLUMBIA, CANADA

Bowser Lake, a fiord lake in the northern Coast Mountains of British C olumbia, contains a thick Holocene fill consisting mainly of silt and clay varves. These sediments were carried into the lake by proglacial Bowser River which drains a high-energy, heavily glacierized basin. Se dimentation in the lake is controlled by seasonal snow and ice melt, b y autumn rainstorms, and by rare, but very large jokulhlaups from glac ier-dammed lakes in the upper Bowser River basin which complicate envi ronmental inferences from the sedimentary record. Sediment is disperse d through the deep western part of the lake by energetic turbidity cur rents. The turbidity currents apparently do not overtop a sill that se parates the western basin from much shallower areas to the east. Large amounts of silt and clay are deposited from suspension in the eastern part of the lake, but sediment accumulation rates there are much lowe r than to the west. Several strong acoustic reflectors punctuate the v arved fill in the western basin; these may be thick or relatively coar se beds deposited during jokulhlaups or exceptionally large storms. Th e contemporary sediment yield to Bowser Lake, estimated from sediments in the lake, is about 360 t km(-2) a(-1). This is a relatively high v alue, but it is less than yields in some other, similar montane basins with extensive snow and ice cover. The most likely explanation for th e difference is that large amounts of sediment have been, and continue to be, stored on the Bowser delta and in small proglacial lakes.