HR: 14:25h
AN: C33D-04    [Abstracts]
TI: The Influence of a Subglacial Dilatant Till Beneath the Upstream Reaches of Bindschadler Ice Stream: Implications for Streaming Ice Flow
AU: * Peters, L E
EM: lpeters@geosc.psu.edu
AF: The Pennsylvania State University, Department of Geoscience 503 Deike Building, University Park, PA 16802
AU: Anandakrishnan, S
AF: The Pennsylvania State University, Department of Geoscience 503 Deike Building, University Park, PA 16802
AU: Alley, R B
AF: The Pennsylvania State University, Department of Geoscience 503 Deike Building, University Park, PA 16802
AU: Winberry, J P
AF: The Pennsylvania State University, Department of Geoscience 503 Deike Building, University Park, PA 16802
AU: Blankenship, D D
AF: The University of Texas at Austin, Institute for Geophysics 4412 Spicewood Springs Rd. #600, Austin, TX 78759-8500
AU: Morse, D L
AF: The University of Texas at Austin, Institute for Geophysics 4412 Spicewood Springs Rd. #600, Austin, TX 78759-8500
AU: Smith, A M
AF: British Antarctic Survey, High Cross, Madingley Rd., Cambridge, CB3 0ET United Kingdom
AU: King, E C
AF: British Antarctic Survey, High Cross, Madingley Rd., Cambridge, CB3 0ET United Kingdom
AB: Subglacial sediments play an important role in the streaming ice flow along the Siple Coast of West Antarctica. It has been hypothesized that a soft and deformable bed acts as a lubricant in enhancing ice flow over an otherwise rugged bedrock floor. The only prior observation of a subglacial till along the Siple Coast was beneath Whillans Ice Streams. This single measurement leads to uncertainties about the regional extent and overall importance of tills in ice drainage. We present the results of a reflection seismic experiments performed just upstream of the inferred onset region of Bindschadler Ice Stream. Changes in the reflectivity of a seismic reflector along the ice-bed interface have proven to be useful in determining the subglacial properties along a portion of Bindschadler Ice Stream. The amplitude versus offset (AVO) technique measures how the amplitude of a seismic reflector varies with increasing source to receiver offset (or angle of incidence of the seismic wave relative to a given interface). Using this method, we suggest that the bed of the ice stream is composed of an unconsolidated and saturated sediment layer. The source-receiver geometry of the seismic reflection experiments allowed us to observe arrivals up to an angle of incidence of 30 degrees. The most notable change observed is a 180 degree phase shift of the basal reflection at incidence angles ranging from 12-25 degrees. Analysis of these amplitude variations reveals P-wave velocities of $<$1700m/s and S-wave velocities of $<$200m/s, indicative of a dilatant and possibly deforming till layer. We suggest that this till layer may be closely linked to the channelization and onset of streaming ice flow.
DE: 9310 Antarctica
DE: 7200 SEISMOLOGY
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting