HR: 14:25h
AN: C22A-04    [PDF]
TI: Glacier-Scale Variability of the Subglacial Drainage System: Year-Long Records from Boreholes at Sites Along the Length of a Glacier
AU: * Harper, J T
EM: joelh@uwyo.edu
AF: Department of Geology and Geophysics, University of Wyoming, Box 3006, Laramie, WY 82071 United States
AU: Humphrey, N F
EM: neil@uwyo.edu
AF: Department of Geology and Geophysics, University of Wyoming, Box 3006, Laramie, WY 82071 United States
AU: Pfeffer, W T
EM: pfeffer@tintin.colorado.edu
AF: Institute of Arctic and Alpine Research and Dept. of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, CO 80309 United States
AB: Borehole measurements are used to examine the long time/space evolution of the subglacial drainage system. Over the course of two field seasons more than 50 boreholes were drilled to the bed of Bench Glacier, a temperate valley glacier in Alaska. The holes are located at 15 sites that span the 8 km from the headwall to the terminus of the glacier. Each site has at least two boreholes and one site has a grid of 16 boreholes spaced 20 x 20 m. The ice depth at the sites ranges from 70 to 190 m. Each borehole was fitted with instrumentation for measuring borehole water level and water flow velocity, and some boreholes were also fitted with conductivity and turbidity probes. Data have been collected at 15 minute intervals for a period in excess of one year. The boreholes were also imaged by video camera and used for slug/pump experiments, and high time/space resolution measurements of surface velocity were collected in the vicinity of the borehole grid. Observations reveal important details about the evolution of the subglacial drainage system over the length of the glacier, and over the course of the year: 1) the onset of summer diurnal variations in water pressure does not undergo an up-glacier spatial progression as is commonly assumed; 2) the termination of summer diurnal variations in water pressure is simultaneous along the length of the glacier; 3) the accumulation and ablation areas of the glacier have actively changing, but differing pressure fields; 4) short-lived subglacial events impact all sites along the length of the glacier, including those in the accumulation and ablation areas and those above and below an ice fall. These findings have diverse implications for the processes dictating the time/space evolution of the subglacial drainage system and the link between hydrology and glacier sliding.
UR: http://research.gg.uwyo.edu/joelh/benchglacier
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
DE: 1894 Instruments and techniques
SC: Cryosphere [C]
MN: 2003 Fall Meeting