OUTBURST FLOODS AT BERING GLACIER, ALASKA

The eastern sector of Bering piedmont lobe has been the site of multiple, historic outburst floods dating back to September 1966. U. S. Geological Survey aerial photographs captured a major outburst event midway through the 1966-67 surge. The main feeder conduit actively supplied diminished discharge to multiple ice front vents during the subsequent 27 years of retreat from an outburst sandur that is preserved on the foreland. Flood deposits contain large-scale scour and fill channels produced during the outburst.

Retreat from the 1967 surge limit eventually uncovered a lower threshold over which ice-contact, peripheral drainage flooded in 1989, thus leading to a rapid 14 m drop in lake surfaces and the emergence of an altered eastern sector terrain. Retreat ceased with the onset of the 1993-95 surge, which was abruptly interrupted in late July 1994 by the sudden flood discharge reactivation of the 1966 subglacial conduit system. The combined erosional and depositional effect was to develop three proglacial sandar, two subglacial scour basins within tunnel channels, and the accumulation of esker materials within englacial voids.

Stratigraphic evidence of Neoglacial outburst(s) is well expressed in several meter-thick boulder zones bound above and below by conventional outwash. These contain, striated sub-meter boulders held within an unsorted sandy/pebbly matrix. Fabric data, scour and fill lower contacts, and crude graded bedding favor deposition by high discharge, tractive flow attributed to flood conditions.

Continues ice front retreat from the 1995 surge maximum is progressing toward the 1989 threshold, with an anticipated outburst during the 2006 ablation season.