Mechanical and hydrologic properties of Whillans Ice Stream till: Implications for basal strength and stick-slip failure

AbstractWe summarize new observations of the deceleration and stick–slip motion of Whillans Ice Stream (WIS), Antarctica. We refine the location of the large sticky spots that resist motion between slip events, the locations of which are controlled by the patterns of subglacial water flow. Our examination of the long-term velocity time series for the ice stream reveals that the decadal-scale deceleration is not occurring at a steady rate, but varies at the sub-decadal timescale. This unsteady deceleration modulates the temporal evolution of a broad (~50 km across) surface-elevation bulge forming at the junction between the relatively narrow upstream portion of the ice stream and broad ice plain that constitutes the downstream end of WIS. Comparison of observations from April 2003 and November 2010 reveals significant changes in the tidally modulated stick–slip cycle that regulates motion on the ice plain. We observe that the timing of slip events has become less regular in response to decreased flow speed in the upstream portions of the ice stream. The decreased regularity of slip events has reduced the release of stored elastic strain during slip events, increasing the rate of deceleration.

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Dynamics of Stick-Slip Motion, Whillans Ice Stream, Antarctica

Quaternary International ◽

10.1016/j.quaint.2012.08.1876 ◽

2012 ◽

Vol 279-280 ◽

pp. 536

Author(s):

J. Paul Winberry

Keyword(s):

Stick Slip ◽

Ice Stream ◽

Whillans Ice Stream ◽

Stick Slip Motion ◽

Slip Motion

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Stick–slip behavior of ice streams: modeling investigations

Annals of Glaciology ◽

10.3189/172756409789624274 ◽

2009 ◽

Vol 50 (52) ◽

pp. 87-94 ◽

Cited By ~ 42

Author(s):

Olga V. Sergienko ◽

Douglas R. MacAyeal ◽

Robert A. Bindschadler

Keyword(s):

West Antarctica ◽

Ice Streams ◽

Stick Slip ◽

Ice Stream ◽

Whillans Ice Stream ◽

Spatial Propagation ◽

The Difference ◽

Stick Slip Motion ◽

Transitional Phase ◽

Slip Motion

AbstractA puzzling phenomenon of ice-stream flow is the stick–slip motion displayed by Whillans Ice Stream (WIS), West Antarctica. In this study we test the hypothesis that the WIS stick–slip motion has features similar to those of other known stick–slip systems, and thus might be of the same origin. To do so, we adapt a simple mechanical model widely used in seismology to study classic stick–slip behavior observed in tectonic faults, in which the difference between static and dynamic friction allows for the generation and spatial propagation of abrupt slip events. We show how spatial variability in friction properties, as well as a periodic forcing intended to mimic the effect of tides, can reproduce the observed duration and periodicity of stick–slip motion in an ice stream. An intriguing aspect of the association of WIS with mechanical stick–slip oscillators is that the onset of stick–slip cycling from a condition of permanent slip appears to be associated with the reduction in overall speed of WIS. If this association is true, then stick–slip behavior of WIS is a transitional phase of behavior associated with the ice stream's recent deceleration.

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Tidally driven stick–slip motion in the mouth of Whillans Ice Stream, Antarctica

Annals of Glaciology ◽

10.3189/172756403781816284 ◽

2003 ◽

Vol 36 ◽

pp. 263-272 ◽

Cited By ~ 49

Author(s):

Robert A. Bindschadler ◽

Patricia L. Vornberger ◽

Matt A. King ◽

Laurie Padman

Keyword(s):

High Tide ◽

Spring Tide ◽

Shear Stresses ◽

Motion Events ◽

Stick Slip ◽

Ice Stream ◽

Whillans Ice Stream ◽

Stick Slip Motion ◽

Tide Period ◽

Slip Motion

AbstractWe show that the ice plain in the mouth of Whillans Ice Stream (formerly Ice Stream B), Antarctica, moves by stick–slip motion. During a spring-tide period, rapid motions regularly occur near high tide and during falling tide. This correlation is weaker during a neap-tide period when the tidal magnitudes are less. Precise timing of these motion events suggests that they propagate through the region with a mean velocity of 88 m s−1.We hypothesize that this speed is associated with the propagation of 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 stored elastic strain 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 by the increase of shear stresses from sub-shelf ocean currents during falling tide. Event magnitudes are not related to the length of the preceding quiescent period, suggesting significant viscous dissipation within the till.

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Seismic and geodetic evidence for grounding-line control of Whillans Ice Stream stick-slip events

Journal of Geophysical Research Earth Surface ◽

10.1002/2013jf002842 ◽

2014 ◽

Vol 119 (2) ◽

pp. 333-348 ◽

Cited By ~ 31

Author(s):

Martin J. Pratt ◽

J. Paul Winberry ◽

Douglas A. Wiens ◽

Sridhar Anandakrishnan ◽

Richard B. Alley

Keyword(s):

Stick Slip ◽

Ice Stream ◽

Whillans Ice Stream ◽

Grounding Line

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Imaging the poro-elastic properties of glacier beds using ambient seismic noise monitoring : application to Whillans ice stream, Antarctica

10.5194/egusphere-egu2020-11594 ◽

2020 ◽

Author(s):

Aurélien Mordret ◽

Gauthier Guerin ◽

Diane Rivet ◽

Brad Lipovsky ◽

Brent Minchew

Keyword(s):

Wave Velocity ◽

Seismic Noise ◽

Large Scale ◽

High Rate ◽

Ambient Seismic Noise ◽

Sediment Layer ◽

Seismic Velocities ◽

Stick Slip ◽

Ice Stream ◽

Whillans Ice Stream

<p>Part of the movement that occurs on all glaciers in Antarctica is a continuous and stable movement that unloads the ice into the sea. The Whillans Ice Plain (WIP) is a portion of the Whillans ice stream that measures 8000 km&#178; for an ice thickness of 800 meters. This glacier has a unique characteristic of moving thanks to tidally modulated stick-slip events twice a day. The slip speed varies laterally across the glacier. &#160;We measured surface wave velocity variations computed from ambient seismic noise cross-correlation. The cross-correlations make it possible to monitor temporally and spatially the seismic velocities at the bed of the glacier, associated with changes in poro-elastic parameters and frictional properties of the glacial till. We averaged our observations for the 78 stick-slip events of our dataset and managed to achieve a 5 min temporal resolution along the 45 min long slip events. The results show a decrease in velocity of about 9% of the S-wave velocity in the subglacial sediment layer about 30 minutes after the initiation of the slip. This velocity drop mainly affects the central part of the glacier. A 10% increase in porosity could induce this velocity decrease due to dilatancy. Dilatant strengthening results from this porosity increase, which in turn keeps the glacier in a slow-sliding regime. The high rate of seismic cycles on such a large scale makes the Whillans ice stream a unique laboratory to study transient aseismic slips in glacial context but also in active tectonic faults one.&#160;</p>

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Thickness changes on Whillans Ice Stream and Ice Stream C, West Antarctica, derived from laser altimeter measurements

Journal of Glaciology ◽

10.3189/172756503781830683 ◽

2003 ◽

Vol 49 (165) ◽

pp. 223-230 ◽

Cited By ~ 13

Author(s):

Vandy Blue Spikes ◽

Beáta M. Csatho ◽

Gordon S. Hamilton ◽

Ian M. Whillans

Keyword(s):

Average Rate ◽

West Antarctica ◽

Laser Altimeter ◽

Equivalent Thickness ◽

Thickness Change ◽

Airborne Laser ◽

Ice Stream ◽

Whillans Ice Stream ◽

Elevation Changes ◽

Global Sea Level

AbstractRepeat airborne laser altimeter measurements are used to derive surface elevation changes on parts of Whillans Ice Stream and Ice Stream C, West Antarctica. Elevation changes are converted to estimates of ice equivalent thickness change using local accumulation rates, surface snow densities and vertical bedrock motions. The surveyed portions of two major tributaries of Whillans Ice Stream are found to be thinning almost uniformly at an average rate of ∼1 m a−1. Ice Stream C has a complicated elevation-change pattern, but is generally thickening. These results are used to estimate the contribution of each surveyed region to the current rate of global sea-level rise.

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Melting and freezing beneath the Ross ice streams, Antarctica

Journal of Glaciology ◽

10.3189/172756504781830295 ◽

2004 ◽

Vol 50 (168) ◽

pp. 96-108 ◽

Cited By ~ 75

Author(s):

Ian Joughin ◽

Slawek Tulaczyk ◽

Douglas R. MacAyeal ◽

Hermann Engelhardt

Keyword(s):

Steady Flow ◽

Temperature Model ◽

West Antarctica ◽

Ice Streams ◽

Horizontal Advection ◽

Ice Stream ◽

Whillans Ice Stream ◽

Shear Heating ◽

Strain Heating ◽

Inland Ice

AbstractWe have estimated temperature gradients and melt rates at the bottom of the ice streams in West Antarctica. Measured velocities were used to include the effects of horizontal advection and strain heating in the temperature model and to determine shear heating at the bed. Our modeled temperatures agree well with measured temperatures from boreholes in regions of steady flow. We find that ice-stream tributaries and the inland ice account for about 87% of the total melt generated beneath the Ross ice streams and their catchments. Our estimates indicate that the ice plains of Whillans Ice Stream and Ice Stream C (even when active) have large areas subject to basal freezing, confirming earlier estimates that import of water from upstream is necessary to sustain motion. The relatively low melt rates on Whillans Ice Stream are consistent with observations of deceleration over the last few decades and suggest a shutdown may take place in the future, possibly within this century. While there are pockets of basal freezing beneath Ice Streams D and E, there are larger areas of basal melt that produce enough melt to more than offset the freezing, which is consistent with inferences of relatively steady flow for these ice streams over the last millennium.

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