Glaciological and geological implications of basal-ice accretion in overdeepenings

Glaciers commonly erode rock basins, also called overdeepenings. Hooke suggested that erosion steepens the adverse slopes on the downglacier sides of overdeepenings until supercooling of subglacial water flow causes ice growth that plugs water channels and reduces the sediment transport needed for further steepening. Erosion then would be localized on the upglacier, headwall sides of overdeepenings, causing overdeepenings to migrate upglacier over time. We hypothesize that an increasing icesurface slope would reduce or eliminate supercooling of water flowing from an overdeepening, allowing erosional steepening of the adverse slope. Subsequent decrease in ice-air surface slope would favor supercooling and accretion of debris-rich basal ice accompanied by sediment deposition in the overdeepening from disruption of subglacial streams. We further hypothesize that glacial erosion rates and sediment yield depend sensitively on the interactions of subglacial water with bedrock-floored and sediment-floored overdeepenings.