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Abstract
Diurnal Stick-Slip Motion in the Mouth of Whillans Ice Stream, Antarctica Robert Bindschadler Patricia Vornberger Matt King Laurie Padman We show that the ice plain in the mouth of Whillans Ice Stream (formerly ice stream B) moves by stick slip motion. During spring-tide periods, rapid motions regularly occur near high tide and during falling tide. This correlation is weaker during neap tides when the tidal magnitudes are less. Precise timing of events suggests that they propagate through the region with a velocity in the range of 53 to 83 meters per second. We hypothesize that this speed is associated with the propagation shear waves through a wet subglacial till. Motion events are also seen on more smoothly flowing floating ice. Event delays are very short between grounded and floating stations, suggesting the events propagate through the ice shelf as an elastic wave. We further hypothesize the events are caused by the interaction of a sticky bed, the accumulation of stress through the compression of ice by upstream inflow, and tidal forcing. Motion events seem to be triggered either by reduction of vertical normal stresses at high tide or the increase of shear stresses from sub-shelf currents during falling tide. |
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