DELTA SLOPE PROCESSES AND TURBIDITY CURRENTS IN PRODELTAIC SUBMARINE CHANNELS, QUEEN INLET, GLACIER BAY, ALASKA

Large submarine channels lead away from the coarse-grained fjord-head delta in Queen Inlet, Glacier Bay, Alaska. Coarse sediment loads from Carroll Glacier are transported down the delta foreslope and through the submarine channels, and finer material is dispersed throughout the fjord from overflow plumes. Slides and slumps occur intermittently on the delta foreslope. A recording current meter positioned in a submarine channel 1 m above the bottom and 2.7 km seaward from the delta brink indicated during July 1989 predominantly quasi-continuous downfjord currents, although several small surges were also observed. Flows occurred throughout the daily tidal cycle in both neap and spring periods for intervals of up to several hours, often beginning and ending rapidly. Current velocities ranged from 0 to 120 cm.s-1, averaging 12 cm.s-1 over one 56 h period, and 16 cm.s-1 over a 13 h period. Suspended sediment concentrations 1 m above bottom commonly exceeded 2 g.L-1 and attained 8.2 g.L-1. The density added to the bottom flow by high turbidity compensated for density lowered by a slight decrease of salinity attained through mixing with fresh meltwater. The contrast between sporadic surges on the delta foreslope and predominantly quasi-continuous turbidity currents downstream in the submarine channels is interpreted as due to attenuation and overlapping of sediment gravity flows of various sizes and velocities originating at the delta front. The relatively low-density, low-velocity, quasi-continuous currents transport large volumes of sediment through the channels, and probably play an important role in maintaining channel form.