HR: 0800h
AN: C41B-0480    [Abstracts]
TI: Overcharging the Subglacial Hydrologic Network: Sliding at Kennicott Glacier, Alaska, When Water Inputs Exceed Outputs
AU: * Anderson, R S
EM: robert.s.anderson@colorado.edu
AF: INSTAAR and Department of Geological INSTAAR and Department of Geological Sciences, University of Colorado, Boulder, CO 80309, United States
AU: Bartholomaus, T C
EM: timothy.bartholomaus@colorado.edu
AF: INSTAAR and Department of Geological INSTAAR and Department of Geological Sciences, University of Colorado, Boulder, CO 80309, United States
AU: Anderson, S P
EM: robert.s.anderson@colorado.edu
AF: INSTAAR and Department of Geography, University of Colorado, Boulder, CO 80309, United States
AB: Basal sliding of Kennicott Glacier, Alaska, occurs when water storage within the glacier is increasing. During the 2006 melt season, we deployed five GPS receivers on the ice surface along the glacier centerline, lake level sensors in four ice-marginal lakes, a stage sensor above the glacier outlet river, and temperature sensors on the ice surface. Outlet water chemistry was monitored with a conductivity sensor and near-daily water samples. These instruments allowed us to assess the relationship between ice motion and glacier hydrology at 1 hr or finer resolution and indicate that when water is entering the glacier faster than it drains out, ice surface velocity increases on both diurnal and seasonal timescales. The largest increase in ice surface speed occurred on a third timescale, that of the outburst of ice-dammed Hidden Creek Lake 15 km from the terminus. During the peak in rate of water storage in the glacier during the jokulhlaup, ice surface motion below the lake increased to 3.0 m/d, up to 6 times faster than non-flood times. Low solute concentrations in the river discharge from the terminus during periods of increasing storage support the view that water from the linked cavity system is prevented from leaving the subglacial hydrologic network by an over-pressurized conduit system. When water inputs exceed what conduits can transmit, the system develops backpressure, and the cavity-to-conduit hydraulic gradients expected in steady state are reversed. The pressurized conduits drive water into and increase pressure in the linked cavity system, promoting basal sliding. A simple numerical model, driven by a calculated water balance time series, predicts water partitioning between the subglacial and englacial reservoirs and ice motion at speeds that closely resemble the observed speeds. These observations and models suggest that persistent high melt rates will not sustain high sliding rates, as over time, the efficiency of the subglacial conduit system will increase. However, large discrete inputs of water to the bed can incite hydraulic transients and associated sliding, potentially explaining recent accelerations of the Greenland Ice Sheet, where rapid drainage of large melt ponds delivers water through cold polar ice.
DE: 0720 Glaciers
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 1719 Hydrology
DE: 1815 Erosion
DE: 1827 Glaciology (0736, 0776, 1863)
SC: Cryosphere [C]
MN: 2007 Fall Meeting