Cyclic steps on a glacifluvial delta, Howe Sound, British Columbia

Abstract

Howe Sound is a deep, steep-walled fjord on Canada's west coast. The primary sediment source is the glacially fed Squamish River. In the inner fjord, turbidity currents flow from the sandy Squamish River Delta at the fjord head reaching as far as the Porteau Creek Sill 15 km to the south. Recent observations from the Squamish Delta have shown that turbidity currents of various volumes are generated daily throughout almost a month of the summer meltwater period and flow through very active submarine channels characterized by active upstream-migrating cyclic step bedforms (Hughes Clarke et al. 2012 a ). Cyclic step bedforms are observed in other turbidity-current environments including the Fraser Delta (Hill 2012; Lintern et al. 2016) and Monterey Canyon (Fildani et al. 2006). The upper foreset slope of the Squamish Delta, is characterized by five incised submarine channels (Fig. 1a). The three northernmost of these channels are active while the two southernmost channels appear to have been abandoned after the artificial diversion of the Mamquam River in 1971. The younger channels and the …