HR: 14:25h
AN: C13A-04    [Abstracts]
TI: Rapid Sediment Erosion and Drumlin Formation Observed Beneath a Fast-Flowing Antarctic Ice Stream
AU: * Smith, A M
EM: amsm@bas.ac.uk
AF: British Antarctic Survey, High Cross Madingley Road, Cambridge, CB3 0ET United Kingdom
AU: Murray, T
EM: t.murray@swansea.ac.uk
AF: University of Wales, Swansea, Singleton Park, Swansea, SA2 8PP United Kingdom
AU: Nicholls, K W
EM: kwni@bas.ac.uk
AF: British Antarctic Survey, High Cross Madingley Road, Cambridge, CB3 0ET United Kingdom
AU: Makinson, K
EM: kmak@bas.ac.uk
AF: British Antarctic Survey, High Cross Madingley Road, Cambridge, CB3 0ET United Kingdom
AU: Adalgeirsdottir, G
EM: g.adalgeirsdottir@swansea.ac.uk
AF: University of Wales, Swansea, Singleton Park, Swansea, SA2 8PP United Kingdom
AU: Behar, A E
EM: Alberto.E.Behar@jpl.nasa.gov
AF: NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA CA 91109 United States
AB: What happens beneath a glacier affects both the way it flows and the landforms left behind when it retreats. Unfortunately, although the subglacial environment is one of the most critical to understanding ice flow and the processes of bedform formation, it is also the most difficult to study. As part of the RABID project on Rutford Ice Stream, West Antarctica in 2004/05, seismic reflection data were acquired at the same geographic location as identical surveys conducted 7 and 13 years previously. Analysis of the data from all 3 seismic surveys gives both the bed topography and an indication of the bed material and basal conditions. In particular, we can distinguish between places where the bed is soft, water-saturated sediments, probably deforming pervasively with the motion of the overlying ice, and those where the bed, whilst still sedimentary, is harder and the ice flow is probably dominated by basal sliding. Over the six years between the first and second surveys, 6 m of sediment was eroded from a region of the bed approximately 500 m wide. This occurs in one of the basal sliding areas. Typical interpreted and modelled subglacial erosion rates from all glacial environments are normally of the order of 0.1-100 mm/a. Our minimum observed rate of 1 m/a is remarkably high, particularly for a glacier which appears to have been in overall steady-state for at least many hundreds of years, and probably much longer. Over the seven years between the second and third surveys, further major changes occurred at the ice stream bed. The previous erosion ceased. Subsequently, a large mound of deforming sediment over-rode this same area of the glacier bed. This mound is 10 m high, 100 m wide and at least a few hundred metres long. This is a very short time for the formation of such a large feature, only 7 years previously nothing of its kind existed at this location. We interpret these dimensions and sediment characteristics as an actively-forming drumlin. Our results are the first observations from a modern glacial analogue of processes that have so far only been modelled theoretically or interpreted from former glaciated regions. They allow us to discriminate between a number of different theories of subglacial erosion and bedform generation as well as quantifying the rates of a number of subglacial processes.
DE: 0720 Glaciers
DE: 0730 Ice streams
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 9310 Antarctica (4207)
SC: Cryosphere [C]
MN: Fall Meeting 2005