Subglacial hydraulic scouring and deposition during surge-related outburst floods, Bering Glacier, Alaska

Fed by a persistent conduit system, three outburst floods released pressurized water from subglacial conduits midway through the 1993-95 surge of Bering Glacier, Alaska. The foreland substrate was mobilized and streamlined by overriding ice, but the effects of hydraulic erosion and deposition were far more effective in altering overridden terrain. Two sub-kilometer basins were scoured decameters into foreland terrain immediately up-glacier from outburst flood sites. These emerged fully formed from beneath the retreating glacier. Flood deposits in scoured subglacial channels consist of meter-size lag boulders beneath meters of well-sorted, graded gravel couplets. Eskers consisting of flood deposits formed within subglacial conduits during outburst flood events were exposed during retreat. Knowledge of pre-surge topography combined with foreland stratigraphy provides a basis for the recognition of subglacial, paleo-flood landforms and deposits.