THE PARADOX OF OVERRIDING ICE: LANDFORM CONTINUITY COUPLED WITH DYNAMIC CHANGE, BERING GLACIER, ALASKA

The Bering Glacier piedmont lobe has a peripheral drainage system and a decadinal history of surge events when it overrides and retreats from an outwash foreland. The most profound resulting terrain modification is from subglacial water processes, whereas the direct effects of overriding ice are comparatively minimal. The terrain appears only slightly altered by the effects of repeated advances that produced fluted drumlinoid ridges, small-scale basal fracture fills, and a veneer of deformation till. Unanticipated are recurrent low-relief, pond-forming depressions between drumlinoid ridges in exactly the same location following successive surge events. In contrast, pressurized subglacial meltwater movement toward ice front outburst sites eroded tunnel channels containing isolated, sub kilometer-size basins, some with ice-cored lag gravel. At a larger, kilometer scale, tunnel erosion has produced an ice-contact basin fitting the size, shape, orientation, and setting of a tunnel valley. The most profound geomorphic changes of the last several decades are due to ice-marginal, fluvial and lacustrine processes that transformed a peripheral limnic environment into to a series of braided sand plains.