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Possible Stick-Slip Mechanism for Whillans Ice StreamTidally-induced stick-slip motion in the mouth of Whillans Ice Stream provides a unique natural experiment in ice-stream response behavior and from which we might learn a great deal about subglacial till properties and sub-ice-stream conditions. At the IGS Symposium on Fast Glacier Flow (Yakutat, 2002), we reported our observations of stick- slip motion and demonstrated its synchronicity with tidal forcing. Recently, we have completed additional processing of our GPS data in differential mode. It reveals more details of the stick-slip events and illustrates that within 30 seconds, the temporal interval of our data, the ice stream accelerates to a speed corresponding to a completely lubricated bed. While details of individual events vary, there seems to be strong evidence of an elastic rebound on the time scale of one hour following most events. This suggests the event involves the release of stored elastic strain energy in the ice. The similar displacements of events suggest further that till or subglacial hydrologic properties limit the amount of elastic strain released in any single event. We follow a line of reasoning that dilatant strengthening limits the slip displacement and present model of the stick-slip process. To match the observed delay between the peak ocean tide and stick-slip events, our model includes a propagating pressure wave in the subglacial hydrologic system between the grounding line, where the rising tide first increases the subglacial water pressure and regions upstream where stored elastic strain increases the basal shear stress. This high-tide event is released when the increased water pressure reaches the region of increased shear stress. Dilatant strengthening stops the event by increasing pore volume and lowering the water pressure. Following this event, falling tide increases the normal forces, compresses the till and increases pore pressure again, leading to the second falling-tide event we observe every tidal cycle.
Document ID
20040013176
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Bindschadler, Robert
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
King, Matt
(Newcastle Univ. Newcastle, United Kingdom)
Vornberger, Patricia
(Science Applications International Corp. Beltsville, MD, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 2003
Subject Category
Oceanography
Meeting Information
Meeting: 7th International Symposium on Antaractic Glaciology
Location: Milan
Country: Italy
Start Date: August 25, 2003
End Date: August 29, 2003
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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