HR: 15:25h
AN: C12B-07    [PDF]
TI: An Investigation Into the Causes and Limiting Factors of an Active Rift on the Amery Ice Shelf: Fieldwork and Modeling Results
AU: * Bassis, J N
EM: jbassis@ucsd.edu
AF: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, La Jolla, CA 92093-0225 United States
AU: Fricker, H
AF: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, La Jolla, CA 92093-0225 United States
AU: Coleman, R
AF: Antarctic Climate and Ecosystem CRC and School of Geography and Environmental Studies, University of Tasmania, Hobart, TAS 7001 United States
AU: Minster, B
AF: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, La Jolla, CA 92093-0225 United States
AB: The Amery Ice Shelf rift system, colloquially known as the "Loose Tooth", consists of two longitudinal (parallel-to-flow) rifts that formed about 15 years ago, and two transverse rifts that together with the western longitudinal rift, form a triple junction. A variety of satellite imagery spanning more than one decade has shown that the transverse rifts have both been actively propagating over the past decade, and have been, on average, speeding up (Young et al, this session). This past Antarctic field season (2002-2003), we instrumented the main transverse rift with 6 GPS and 8 vertical component seismometers. Results indicate that there are several periods of high seismic activity during which the rift widens rapidly. Comparison of experimental values of the critical stress intensity factor (a measure of the strength of the ice) with the stress acting at the tip of the rift calculated for an elastic ice shelf, suggest that the rift should propagate unstably. In an attempt to resolve this paradox we consider two possible explanations. First we examine the effect of a viscoelastic rheology of ice on dissipation of the stress at the tip of the rift; the associated time scale competes with the time scales attached to the loading mechanisms which control the rate of stress accumulation. In contrast the effect of an array of longitudinal crevasses on the stress field concentrated ahead of the rift is largely geometrical. Rift propagation is hindered because the crevasses create areas that are effectively weaker than the surrounding ice. We use a boundary element model to evaluate the effect of an array of crevasses on the stress concentrated at the tip of the rift.
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
DE: 7205 Continental crust (1242)
SC: Cryosphere [C]
MN: 2003 Fall Meeting