HYDROLOGY, EROSION AND SEDIMENT PRODUCTION IN A SURGING GLACIER - VARIEGATED GLACIER, ALASKA, 1982-83

Outlet streams of Variegated Glacier, Alaska, U.S.A., were observed before, during and after the surge of 1982-83. Measurements of discharge, suspended sediment and dissolved load in the outlet streams are presented for the years 1982-84, and comparisons are made with data from previous years. The data are interpreted to yield characteristics of the basal hydraulic system. The surging region of the glacier was underlain by a basal hydraulic zone of low water velocity and high water storage, inferred to be a distributed-now system. The ice down-glacier of the propagating surge front was underlain by a high-velocity, low-storage zone, inferred to be a conduit system. The volume of water stored above the surge front was the major hydraulic control on the surge. Basal bedrock erosion during the surge was extreme in comparison to non-surging glaciers. The sediment output was directly proportional to the basal sliding, with a dimensionless erosion rate (meters eroded from the bed divided by meters of sliding) of order 1.0 x 10(-4). Total erosion during the 20 year surge cycle was on the order of 0.3 m of bedrock, with approximately two-thirds occurring during the 2 years of the surge peak, and the bulk of this during the peak 2 months.