scholarly journals Bathymetry and geological structures beneath the Ross Ice Shelf at the mouth of Whillans Ice Stream, West Antarctica, modeled from ground-based gravity measurements

2013 ◽  
Vol 118 (8) ◽  
pp. 4535-4546 ◽  
Author(s):  
Atsuhiro Muto ◽  
Knut Christianson ◽  
Huw J. Horgan ◽  
Sridhar Anandakrishnan ◽  
Richard B. Alley
Keyword(s):  
West Antarctica ◽  
Ice Shelf ◽  
Geological Structures ◽  
Ross Ice Shelf ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
Gravity Measurements

scholarly journals Changes in the ice plain of Whillans Ice Stream, West Antarctica

2005 ◽  
Vol 51 (175) ◽  
pp. 620-636 ◽  
Author(s):  
Robert Bindschadler ◽  
Patricia Vornberger ◽  
Laurence Gray
Keyword(s):  
West Antarctica ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
Grounding Line ◽  
Local Areas ◽  
The Mean ◽  
Geometric Changes ◽  
Thinning Rate

AbstractData from the mouth of the decelerating Whillans Ice Stream (WIS), West Antarctica, spanning 42 years are reviewed. Deceleration has continued, with local areas of both thinning and thickening occurring. The mean thinning rate is 0.48 ± 0.77 ma–1. No consistent overall pattern is observed. Ice thickens immediately upstream of Crary Ice Rise where deceleration and divergence are strongest, suggesting expanded upstream influence of the ice rise. Thinning is prevalent on the Ross Ice Shelf. Grounding-line advance at a rate of 0.3 km a–1 is detected in a few locations. Basal stresses vary across an ice-stream transect with a zone of enhanced flow at the margin. Marginal shear is felt at the ice-stream center. Mass-balance values are less negative, but larger errors of earlier measurements mask any possible temporal pattern. Comparisons of the recent flow field with flow stripes suggest WIS contributes less ice to the deep subglacial channel carved by Mercer Ice Stream and now flows straighter. The general lack of geometric changes suggests that the regional velocity decrease is due to changing basal conditions.

scholarly journals Timing of stagnation of Ice Stream C, West Antarctica, from short-pulse radar studies of buried surface crevasses

1993 ◽  
Vol 39 (133) ◽  
pp. 553-561 ◽  
Author(s):  
Rory Retzlaff ◽  
Charles R. Bentley
Keyword(s):  
Short Pulse ◽  
Water Pressure ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Pulse Radar ◽  
West Antarctic ◽  
Ice Stream ◽  
Inland Ice

AbstractFive short-pulse radar profiles were run across the edge of inactive Ice Stream C, one of the “Ross” ice streams that flows from the West Antarctic inland ice sheet into the Ross Ice Shelf. Scatter from buried crevasses, which we presume were at the surface of the ice stream when it was active, creates hyperbolae on the radar records. A density-depth curve and local accumulation rates were used to convert the picked travel times of the apices of the hyperbolae into stagnation ages for the ice stream. Stagnation ages are 130 ± 25 year for the three profiles farthest downstream and marginally less (100 ± 30 year) for the fourth. The profile farthest upstream shows a stagnation age of only ~30 year. We believe that these results indicate a “wave” of stagnation propagating at a diminishing speed upstream from the mouth of the ice stream, and we suggest that the stagnation process involves a drop in water pressure at the bed due to a conversion from sheet flow to channelized water flow.

scholarly journals Basal sliding of Ice Stream B, West Antarctica

1998 ◽  
Vol 44 (147) ◽  
pp. 223-230 ◽  
Author(s):  
Engelhardt Hermann ◽  
Kamb Barclay
Keyword(s):  
West Antarctica ◽  
Ice Shelf ◽  
The West ◽  
Ross Ice Shelf ◽  
Sliding Motion ◽  
Ice Stream ◽  
Grounding Line ◽  
Basal Sliding ◽  
Ice Stream B ◽  
Streaming Motion

AbstractA “tethered stake” apparatus is used to measure basal sliding in a borehole on Ice Stream B, West Antaretica, about 300 km upstream (east) from its grounding line near the head of the Ross Ice Shelf. A metal stake, emplaced at the top of a laver of unfrozen till underlying the ice, is connected by a tether line to a metering unit that measures the tether line as it is pulled out from the borehole by the stake as a result of basal sliding. The measured sliding motion includes any actual slip across the ice–till interface and may include in addition a possible contribution from shear deformation of till within about 3 cm of the interface. This 3 cm figure follows from a qualitative model of the movements of the stake in the course of the experiment, based on features of the record of apparent sliding. Alternative but less likely models would increase the figure from 3 cm to 10 cm or 25 cm. In any case it is small compared to the seismically inferred till thickness of 9 m. Measured apparent sliding averages 69% of the total motion of 1.2 m d−1over 26 days of observation if a 3.5 day period of slow apparent sliding (8% of the total motion) is included in the average. The occurrence of the slow period raises the possibility that the sliding motion switches back and forth between c.80% and c. 8% of the total motion, on a time-scale of a few days. However, it is likely that the period of slow apparent sliding represents instead a period when the stake got caught on the ice sole. If the slow period is therefore omitted, the indicated average basal sliding rate is 83% of the total motion. In either case, basal sliding predominates as the cause of the rapid ice-stream motion. In the last 2 days of observation the average apparent sliding rate reached 1.17 m d−1, essentially 100% of the motion of the ice stream. If till deformation contributes significantly to the ice-stream motion, the contribution is concentrated in a shear zone 3 cm to possibly 25 cm thick at the top of the 9 m thick till layer. These observations, if applicable to the West Antaretic ice sheet in general, pose complications in modeling the rapid ice-streaming motion.

scholarly journals Basal sliding of Ice Stream B, West Antarctica

1998 ◽  
Vol 44 (147) ◽  
pp. 223-230 ◽  
Author(s):  
Engelhardt Hermann ◽  
Kamb Barclay
Keyword(s):  
West Antarctica ◽  
Ice Shelf ◽  
The West ◽  
Ross Ice Shelf ◽  
Sliding Motion ◽  
Ice Stream ◽  
Grounding Line ◽  
Basal Sliding ◽  
Ice Stream B ◽  
Streaming Motion

AbstractA “tethered stake” apparatus is used to measure basal sliding in a borehole on Ice Stream B, West Antaretica, about 300 km upstream (east) from its grounding line near the head of the Ross Ice Shelf. A metal stake, emplaced at the top of a laver of unfrozen till underlying the ice, is connected by a tether line to a metering unit that measures the tether line as it is pulled out from the borehole by the stake as a result of basal sliding. The measured sliding motion includes any actual slip across the ice–till interface and may include in addition a possible contribution from shear deformation of till within about 3 cm of the interface. This 3 cm figure follows from a qualitative model of the movements of the stake in the course of the experiment, based on features of the record of apparent sliding. Alternative but less likely models would increase the figure from 3 cm to 10 cm or 25 cm. In any case it is small compared to the seismically inferred till thickness of 9 m. Measured apparent sliding averages 69% of the total motion of 1.2 m d−1over 26 days of observation if a 3.5 day period of slow apparent sliding (8% of the total motion) is included in the average. The occurrence of the slow period raises the possibility that the sliding motion switches back and forth between c.80% and c. 8% of the total motion, on a time-scale of a few days. However, it is likely that the period of slow apparent sliding represents instead a period when the stake got caught on the ice sole. If the slow period is therefore omitted, the indicated average basal sliding rate is 83% of the total motion. In either case, basal sliding predominates as the cause of the rapid ice-stream motion. In the last 2 days of observation the average apparent sliding rate reached 1.17 m d−1, essentially 100% of the motion of the ice stream. If till deformation contributes significantly to the ice-stream motion, the contribution is concentrated in a shear zone 3 cm to possibly 25 cm thick at the top of the 9 m thick till layer. These observations, if applicable to the West Antaretic ice sheet in general, pose complications in modeling the rapid ice-streaming motion.

scholarly journals Timing of stagnation of Ice Stream C, West Antarctica, from short-pulse radar studies of buried surface crevasses

1993 ◽  
Vol 39 (133) ◽  
pp. 553-561 ◽  
Author(s):  
Rory Retzlaff ◽  
Charles R. Bentley
Keyword(s):  
Short Pulse ◽  
Water Pressure ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Pulse Radar ◽  
West Antarctic ◽  
Ice Stream ◽  
Inland Ice

AbstractFive short-pulse radar profiles were run across the edge of inactive Ice Stream C, one of the “Ross” ice streams that flows from the West Antarctic inland ice sheet into the Ross Ice Shelf. Scatter from buried crevasses, which we presume were at the surface of the ice stream when it was active, creates hyperbolae on the radar records. A density-depth curve and local accumulation rates were used to convert the picked travel times of the apices of the hyperbolae into stagnation ages for the ice stream. Stagnation ages are 130 ± 25 year for the three profiles farthest downstream and marginally less (100 ± 30 year) for the fourth. The profile farthest upstream shows a stagnation age of only ~30 year. We believe that these results indicate a “wave” of stagnation propagating at a diminishing speed upstream from the mouth of the ice stream, and we suggest that the stagnation process involves a drop in water pressure at the bed due to a conversion from sheet flow to channelized water flow.

scholarly journals Sensitivity of Pine Island Glacier, West Antarctica, to changes in ice-shelf and basal conditions: a model study

2002 ◽  
Vol 48 (163) ◽  
pp. 552-558 ◽  
Author(s):  
Marjorie Schmeltz ◽  
Eric Rignot ◽  
Todd K. Dupont ◽  
Douglas R. MacAyeal
Keyword(s):  
Shear Stress ◽  
Element Model ◽  
Shelf Area ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Stream ◽  
Model Study ◽  
Grounding Line ◽  
Glacier Velocity ◽  
Basal Shear

AbstractWe use a finite-element model of coupled ice-stream/ice-shelf flow to study the sensitivity of Pine Island Glacier, West Antarctica, to changes in ice-shelf and basal conditions. By tuning a softening coefficient of the ice along the glacier margins, and a basal friction coefficient controlling the distribution of basal shear stress underneath the ice stream, we are able to match model velocity to that observed with interferometric synthetic aperture radar (InSAR). We use the model to investigate the effect of small perturbations on ice flow. We find that a 5.5–13% reduction in our initial ice-shelf area increases the glacier velocity by 3.5–10% at the grounding line. The removal of the entire ice shelf increases the grounding-line velocity by > 70%. The changes in velocity associated with ice-shelf reduction are felt several tens of km inland. Alternatively, a 5% reduction in basal shear stress increases the glacier velocity by 13% at the grounding line. By contrast, softening of the glacier side margins would have to be increased a lot more to produce a comparable change in ice velocity. Hence, both the ice-shelf buttressing and the basal shear stress contribute significant resistance to the flow of Pine Island Glacier.

scholarly journals Basal mechanics of ice streams: Insights from the stick-slip motion of Whillans Ice Stream, West Antarctica

2009 ◽  
Vol 114 (F1) ◽  
Author(s):  
J. Paul Winberry ◽  
Sridhar Anandakrishnan ◽  
Richard B. Alley ◽  
Robert A. Bindschadler ◽  
Matt A. King
Keyword(s):  
West Antarctica ◽  
Ice Streams ◽  
Stick Slip ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
Stick Slip Motion ◽  
Slip Motion

scholarly journals Flow dynamics of the Rutford Ice Stream ice-drainage basin, West Antarctica, from radar stratigraphy

2009 ◽  
Vol 50 (51) ◽  
pp. 42-48 ◽  
Author(s):  
E.C. King
Keyword(s):  
Drainage Basin ◽  
Rapid Change ◽  
Flow Dynamics ◽  
Volume Flux ◽  
West Antarctica ◽  
Ice Shelf ◽  
Main Trunk ◽  
Ice Dynamics ◽  
Ice Volume ◽  
Ice Stream

AbstractRutford Ice Stream, West Antarctica, drains a catchment of >45 000 km2 into the Ronne Ice Shelf through a 26 km wide, 2.4 km deep subglacial trough adjacent to the Ellsworth Mountains. Forty-two per cent of its catchment boundary is common with Pine Island Glacier, where rapid change to ice dynamics is currently underway. These changes may eventually affect adjacent catchments such as Rutford. Radar sounding data were acquired over the Rutford ice-drainage basin that show the internal structure. In particular, distinctive reflector groups were identified that mark the boundaries between four different flow elements. The flow-margin reflector groups include curvilinear events that cross-cut isochrones and are therefore likely to be post-depositional. These reflections may arise from crystal orientation fabrics generated by localized strain in a flow margin. One of the sectors of the ice-drainage basin supplies the largest share (38%) of the ice volume flux through the main trunk of Rutford Ice Stream. This sector may be preferentially affected by continuing surface lowering in the Pine Island Glacier catchment.

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