HR: 0800h
AN: C41A-0041    [Abstracts]
TI: A 700 year-long Record of Glacial Surging and Associate Flooding: Bering Glacier, Alaska.
AU: * Kramer, B J
EM: bjkramer@ufl.edu
AF: University of Florida, 241 Williamson Hall P.O. Box 112120, Gainesville, FL 32611, United States
AU: Jaeger, J M
EM: jaeger@geology.ufl.edu
AF: University of Florida, 241 Williamson Hall P.O. Box 112120, Gainesville, FL 32611, United States
AB: Bering Glacier, Alaska is one of the largest, but until recently, most poorly studied dynamic glaciers in North America, and is largely known for its dramatic surging events, six of which have occurred in historic times. A primary late Holocene history of the Bering has been established from on-shore studies of glacial termini position and evidence of glacial advances, but the Little Ice Age (LIA) record of glacial surging and associated flooding has not been examined. A 14m-long jumbo core collected on the adjacent continental shelf reveals a 700-year-long record of flood deposition. The core was dated using 210Pb chronology and five radiocarbon dates and can be separated into three distinct lithologic units based on examination of x-radiographs and physical properties: 1) the uppermost unit dates from /sim120 yr BP to the present and is characterized by bioturbated mud interbedded with faintly laminated, thick (5-20cm) low-density beds, 2) the middle unit dates from /sim120 /- 300 yr BP and includes abundant laminated-to-interbedded low- and high-density beds with some evidence of bioturbation, and 3) a lowermost unit post dates 300 yr BP and is composed of rare laminated beds grading into mottled to massive mud. In each of these units, the laminated lithofacies from this oxic mid- shelf location indicates both flood and gravity flow deposition. Based on terrestrial studies (Wiles et al, 1999), from 850 /- 400 yr BP, the terminus was at a slightly advanced position relative to the present and was at its Neoglacial maximum extent, which was close to the modern coastline, during the LIA (400 /- /sim200 yr BP). The thick low-density, clay-rich beds in the uppermost unit correlate with historic outburst floods associated with known surge events. During the LIA, bioturbated intervals are rare and thin while laminated intervals are common. Given average radiocarbon-established sedimentation rates of 2-3 cm/y, this style of interbedding indicates frequent flood deposition at the core's location. This would suggest that the decadal-long quiescent periods between outburst floods typical of the last century were not prevalent during the LIA. The infrequent deposition of flood layers in the lowermost unit could be attributed to the diversion of glacial drainage to the eastern Kaliakh, Tsiu, and Tsivat Rivers (Muller and Fleisher 1995) instead of present day Seal River. The observation of more frequent flooding events during the LIA differs appreciably from the past century, suggesting that Bering Glacier's hydrology during this period was altered relative to the present conditions that result in quasi-periodic surges.
DE: 0720 Glaciers
DE: 0774 Dynamics
DE: 1821 Floods
DE: 3022 Marine sediments: processes and transport
SC: Cryosphere [C]
MN: 2007 Fall Meeting