Geophysical Studies of the Lateral Transition Zone of an Active Antarctic Ice Stream

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The manner and rate of deformation of the Earth's major ice sheets depend on a complex interplay of their geographical and climatic setting, as well as their internal dynamics. In the West Antarctic Ice Sheet, it is known that rapidly moving ice streams alternate with large areas of stagnant ice, and that the transition between streaming and non-streaming flow can be be quite narrow. In these lateral shear margins it is thought that the physical controls on ice stream dynamics must show significant differences. This study will examine the geophysical differences between an ice stream and a stagnant ridge along the Siple Coast in West Antarctica. The ice will be probed with electromagnetic and seismic waves to infer the internal temperature and the crystalline structure of the ice, as well as the proportion of old (Wisconsin Ice Age) ice, since it is known that ice flow laws depend exponentially on temperature, that ice crystals are much less resistant to deformation in the plane of their hexagonal faces than in other directions, and that old ice may deform much more readily than ice of more recent geological age. Measurement of radar diffraction patterns and the analysis of the records of micro- earthquakes can be used to show whether the base of the ice sheet is frozen to the underlying bedrock.