GLACIOHYDRAULIC EROSION OF AN UNCONSOLIDATED SUBSTRATE, BERING GLACIER, ALASKA

Peat Island overridden during the 1.5 km advance. Exposed are the cumulative effects of glacial scour and deposition, plus extensive erosion caused by the outburst release of stored subglacial water. Post-surge landforms are compared with pre-surge topography to assess the relative significance of overriding ice and glaciohydraulic erosion. The primary subglacial influence of ice was to mobilize, erode and re deposit foreland substrate (diamicton and gravel) as smooth, streamlined knolls, overprinted by flutes on a veneer of new till. However, outburst events caused extensive subglacial incision. Exposed from beneath the retreating ice are fully formed 10-15 m high bluffs, gullies and gorges incised within pre-surge terrain. These appear comparable to features formed by subaerial meltwater streams. Potentially distinguishing characteristics are 1) bluff-walled basins eroded without regard for surface base level, and 2) bluff truncation of streamlined hills in the absence of surface steams. The scale and rate of landform modification by high-discharge, pressurized subglacial water vastly exceeds the erosional effects of overriding ice. The volume of sediment removed by glaciohydraulic excavation is truly astounding and challenge conventional expectations.