DETERMINATION OF ANNUAL GLACIER EROSION RATES IN THE MENDENHALL WATERSHED, JUNEAU, ALASKA

We indirectly measured the rate that the Mendenhall Glacier, near Juneau, Alaska, delivers sediment into the lower Mendenhall Valley. Despite the relatively large erosional magnitude attributed to glaciers, year-to-year glacial erosion processes are difficult to measure directly. The approach taken here was to calculate a sediment budget for the proglacial lake below the Mendenhall Glacier and determine the glacial contributions to the budget indirectly. Direct measures were made of non-glacial sediment fluxes into and out of the lake and changes in sediment volume on the bottom of the lake. Sediment loads from representative up-valley streams and the Mendenhall River, which drains the proglacial lake, were made daily during several periods throughout summer and fall of 2001 and 2002. Discharge data for the Mendenhall River were collected by the USGS. Temperature and precipitation data from the NWS were used to estimate up-valley flow into the lake. Lake bottom sedimentation was measured for a two-month period, July through August 2002 and changes in sediment volume in Mendenhall Lake were determined from bathymetric data collected in 2000 and 2002. The area of the watershed is 220 km2. Data and results through summer 2002 will be reported at this meeting.