HIGH-FREQUENCY TURBIDITY CURRENTS IN BRITISH-COLUMBIA FJORDS

The frequency of turbidity currents in Bute Inlet and Knight Inlet (British Columbia, Canada) was monitored. A prototype instrument (turbidity event detector) was deployed adjacent to prominent incised sea-floor channels. Approximately 25-30 turbidity currents occur annually. They appear closely correlated to periods of higher river discharge into the heads of the fjords. Two peaks in both discharge and turbidity current frequency occur, one in response to snow melt in late June-early July, the other to glacier melt in August. Virtually no turbidity currents were observed in winter. River mouth bars, channel deposits, and other deltaic sediments build up during lower discharge periods and are swept onto the steep delta front and into subaqueous channels, along with bedload, during floods.