FLUX OF DEBRIS TRANSPORTED BY ICE AT 3 ALASKAN TIDEWATER GLACIERS

The stability of a tidewater terminus is controlled by glacial dynamic s, calving processes and sedimentary processes at the grounding line. An investigation of grounding-line sediment dynamics and morainal-bank sediment budgets in Glacier Bay. Alaska, U.S.A., has yielded data tha t enable us to determine the debris fluxes of Grand Pacific, Margerie and Muir Glaciers. Debris flux ranges from 10(5) to 10(6) m(3) a(-1) o ne to two orders of magnitude lower than the glacifluvial sediment flu xes (10(6)-10(7) m(3) a(-1)). Combined, these fluxes represent the hig hest yields known for glacierized basins. Large debris fluxes reflect the combined effects of rapid glacier flow: driven by the maritime cli mate of southeast Alaska; and highly erodible bedrock. Englacial-debri s distribution is affected by valley width and relief both of which co ntrol the availability of sediment. The number of tributaries controls the distribution and volume of debris in englacial and supraglacial m oraines. At the terminus, iceberg-rafting removes up to two orders of magnitude more sediment from the ice-proximal environment than is depo sited by melt-out or is dumped during calving events. Rough estimates of the sediment flux by deforming beds suggests that soft-bed deformat ion may deliver up to an order of magnitude more sediment to the termi nus than is released from within the glacier ice.