SURGING HISTORY AND POTENTIAL FOR RENEWED RETREAT - BERING GLACIER, ALASKA USA

Late Wisconsinan glacial recession uncovered a fiord where now Bering Glacier descends to the Gulf of Alaska coast. At maximum extent in the early Holocene, the fiord may have reached 50 km inland. Gradual glacial readvance may have begun by 6000 yr BP. At least by 4500 yr BP, and throughout the latter part of this advance, the glacier margin was protected against calving by its own sediment apron. Rhythmically involuted medial debris bands record frequent surging in previous centuries and perhaps throughout Neoglacial history. Air photos document surges that culminated about 1940, 1960, and 1968. An hypothesis of 20 to 30 yr surge cyclicity is strengthened by current activity. Between 1968 and 1993, retreat of 2 to 5 km on the east flank of the piedmont lobe exposed buried forest beds and outwash. Basins, eroded in this drift sequence primarily by glacial action, now contain proglacial lakes 50 to 80 m or more in depth. Continued ice recession at recent rates would, within a few years, have caused these several lakes to join as a single lake temporarily retained a few meters above sea level by an unlithified sediment barrier. Glacier retreat into deeper water, and exposure to tidal activity would have induced more active calving were it not for the surge which began in spring 1993. However, unless the current advance is unusually vigorous, it will only temporarily interrupt rather than completely reverse the recent long-term trend toward retreat.