Author(s): Fleisher PJ, Bailey PK, Natal EM, Muller EH, Cadwell DH, Russell AJ
Abstract: During the initial six months of the 1993-95 surge the terminous of the eastern part of the Bering Glacier piedmont lobe advanced between 1.0 to 7.4 m per day, and thickened by an estimated 125 to 150 m. An exceedingly dynamic outburst of highly pressured subglacial water from a persistent conduit system abruptly interrupted the surge one year after it began. Sediment deposited by that flood formed Icewall Sandur in Tsivat Lake. Within months, a second outburst nearly dissected Weeping Peat Island with the resulting construction of Riverhead and Splitlake Sandar. When the surge resumed, ice front advance was intermittent and much slower, leading to the final formation of a prominent push moraine marking the limit of ice advance on the eastern sector. Although basal sliding was a factor in producing surge-related changes along the eastern sector, the most profound alteration of island terrain was the result of outburst-related erosion and deposition during the release of subglacial water. Those changes significantly modified the pro-glacial peripheral drainage system. Only after a decade of retreat was it possible to asses the limited effects of overriding ice, which were confined to deposition of a sub-meter deformation till, decimeter-scale flutes, and drumlinized topography accompanied by flanking truncation of subglacial strata. The dominant modifications to the pre-surge foreland terrain, however, were subglacial hydraulic scouring of basins 15 meters deep, cutting of subglacial bluffs meters to decimeters in relief, and outburst-related pro-glacial sandar development. Primary outbursts sites on Weeping Peat Island related directly to a persistent subglacial conduit system that endured the entire 28-year surge cycle surviving two surges and multiple outburst floods. The surge cycle, originally proposed by Post (1972), spans 28 years beginning with the initiation of surge activity in 1965 through renewed surging in 1993, including a retreat-initiated breakout of a large ice-contact proglacial lake in 1989. Because the 1993-95 surge culminated more than a kilometers short of the 1965-67 surge terminus, a repeat of the 1989 breakout event in 2006 at the same location required a shorter interval of 17 years.
Keywords: surge cyclisty, modified overridden terrain, subglacial hydraulic scouring
|
Professor Andrew Russell
|
|