Sliding of Kennicott Glacier, Alaska, in response to evolution of water storage on annual, diurnal and outburst flood timescales during the 2006 melt season

Basal sliding occurs when water storage within Kennicott Glacier, Alaska, is increasing. During the 2006 melt season, we deployed GPS receivers to the ice surface along the glacier centerline, lake level sensors to ice-marginal lakes, a stage sensor to the glacier outlet river, and temperature sensors to 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, sliding is promoted on diurnal and seasonal timescales. At a third timescale, that of the outburst of a large ice-dammed lake, ice surface motion below the lake increased to 3.0 m/d, up to 6 times faster than non-flood times, while discharge from the lake was increasing and before flooding began on the outlet river. Again, when water storage is increasing, basal sliding speeds are high. Dilute solute concentrations in the discharge from the terminus during periods of increasing storage suggest that water from the linked cavity system is prevented from leaving the subglacial hydrologic network by an over-pressurized conduit system. We hypothesize that during these episodes, water flows from a central conduit into the dispersed linked cavity system and backs water up into englacial fractures and moulins, increasing subglacial water pressures and enhancing sliding. A simple numerical model, driven by the water balance time series we calculate for Kennicott Glacier, predicts water partitioning between the subglacial and englacial reservoirs and ice motion at speeds that closely resemble the observed speeds.