EVENTS ASSOCIATED WITH THE 1993-95 SURGE AND OUTBURST FLOODS, BERING GLACIER, ALASKA

Although specific causes remain elusive, surge events and associated outburst floods at Bering Glacier provide analog conditions for investigations that span topics of broad interest and significance. Post's hypothesis of a 25 - 30 year surge cycle came to fruition during the spring and summer of 1993. Newly formed, anomalous crevasse patterns and a prominent, transverse surface bulge, first noted in the lower Bering trunk and upper piedmont lobe, signaled the early summer movement of energy through the glacier. Within months the chaotically crevassed, much thickened ice front began advancing 3 - 7 m/day onto the eastern foreland, and magnitudes faster into deep lakes. During the two years that followed, ice-marginal environments were elevated to a new level of activity punctuated by two massive outburst floods (jokulhlaups) with calculated discharges that ranged from 8,000 - 32,000 cms. These significantly altered ice-contact and proglacial terrain through the formation of ice-block strewn sandar and brought an end to the surge. Debris bands effaced by densely spaced crevassing reappeared within 2.5 to 3.0 years, thus implying a rate downwasting. Retreat since late 1995 has uncovered conspicuous evidence of subglacial hydraulic scour and deposition far in excess of the fluting effects of overriding ice, which in some areas did little more than deposit a decimeter till mantle. A summary of events associated with the 1993-95 surge and outburst floods, and the resulting modification of eastern foreland terrain will be presented.