AN OUTBURST ESKER, EASTERN SECTOR, BERING GLACIER, ALASKA

Bering Glacier retreat from its 1995 surge limit on Weeping Peat Island progressively exposed (2000-2004) a broad-crested, elongate mound (200 m long, 75 to 100 m wide, and 26 m in relief) of sand and gravel. The mound is oriented perpendicular to the ice front and aligned between a glacier surface collapse moulin (100-200 m diameter) and the ice front discharge site of a mid-surge 1,100 cms outburst flood. At the base of its upglacier bluff is a 6 m thick unit consisting of sub-horizontal, crudely developed rhythmic beds of moderately sorted pebble gravel that alternates with coarse, pebbly sand in couplets 15 to 20 cm thick. The lower contact grades into 4 m of sand containing minor peat seams and is partially obscured by colluvium. The upper contact is a massive, undulating cut-and-fill channel lined with clusters of well rounded, meter-size, lag boulders (similar channels and boulder zones are found elsewhere in foreland outwash). This is capped by 3-4 m of exceptionally well sorted, clast-supported, cobble and boulder gravel dipping six degrees in the upglacier direction. The graded boulder beds fine upward into cobble gravel that rises to intersect the eastern end of the mound where it coincides with previously ice core subsidence. Although limited in length and lacking the classic sinuous form of an esker, this feature is interpreted to be an esker formed during outburst conditions based on 1) alignment between an outburst site and an upglacier collapse moulin, 2) distinctive internal architecture, and 3) dimensions consistent with an englacial and/or subglacial outburst conduit.