scholarly journals Flow of Rutford Ice Stream and Comparison with Carlson Inlet, Antarctica

1989 ◽  
Vol 12 ◽  
pp. 51-56 ◽  
Author(s):  
R.M. Frolich ◽  
D.G. Vaughan ◽  
C.S.M. Doake
Keyword(s):  
Surface Expression ◽  
Ice Thickness ◽  
Shear Stresses ◽  
Lateral Shear ◽  
Ice Stream ◽  
Grounding Line ◽  
Subglacial Topography ◽  
Characteristic Features ◽  
Basal Shear ◽  
Thickness Measurements

Results from movement surveys on Rutford Ice Stream are presented with complementary surface-elevation and ice-thickness measurements. Surface velocities of 300 m a−1 occur at least 130 km up-stream of the grounding line and contrast strongly with the neighbouring Carlson Inlet, where a velocity of 7 m a−1 has been measured. This contrast in velocity is not topographically controlled but appears to be due instead to differences in basal conditions, with Carlson Inlet probably being frozen to its bed. Concentration of lateral shear close to the margins and surface expression of subglacial topography both support a view of significant basal shear stresses in the central part of Rutford Ice Stream. The pattern of principal strain-rate trajectories shows a small number of characteristic features which can be compared with results from future modelling of the glacier's flow.

scholarly journals Flow of Rutford Ice Stream and Comparison with Carlson Inlet, Antarctica

1989 ◽  
Vol 12 ◽  
pp. 51-56 ◽  
Author(s):  
R.M. Frolich ◽  
D.G. Vaughan ◽  
C.S.M. Doake
Keyword(s):  
Surface Expression ◽  
Ice Thickness ◽  
Shear Stresses ◽  
Lateral Shear ◽  
Ice Stream ◽  
Grounding Line ◽  
Subglacial Topography ◽  
Characteristic Features ◽  
Basal Shear ◽  
Thickness Measurements

Results from movement surveys on Rutford Ice Stream are presented with complementary surface-elevation and ice-thickness measurements. Surface velocities of 300 m a−1 occur at least 130 km up-stream of the grounding line and contrast strongly with the neighbouring Carlson Inlet, where a velocity of 7 m a−1 has been measured. This contrast in velocity is not topographically controlled but appears to be due instead to differences in basal conditions, with Carlson Inlet probably being frozen to its bed. Concentration of lateral shear close to the margins and surface expression of subglacial topography both support a view of significant basal shear stresses in the central part of Rutford Ice Stream. The pattern of principal strain-rate trajectories shows a small number of characteristic features which can be compared with results from future modelling of the glacier's flow.

scholarly journals Seismic-reflection evidence for a deep subglacial trough beneath Jakobshavns Isbræ, West Greenland

1996 ◽  
Vol 42 (141) ◽  
pp. 219-232 ◽  
Author(s):  
Ted S. Clarke ◽  
Keiih Echelmeyer
Keyword(s):  
Seismic Reflection ◽  
Dominant Role ◽  
Ice Thickness ◽  
Shear Stresses ◽  
Outlet Glacier ◽  
West Greenland ◽  
Ice Stream ◽  
Surface Slopes ◽  
Radio Echo Sounding ◽  
Basal Shear

AbstractSeismic-reflection methods were used to determine the ice thickness and basal topography of Jakobshavns Isbræ, a large, fast-moving ice stream/outlet glacier in West Greenland. A method of data analysis was developed which involves the pointwise migration of data from a linear seismic array and a single explosive source; the method yields the depth, horizontal position and slope of the basal reflector. A deep U-shaped subglacial trough was found beneath the entire length of the well-defined ice stream. The trough is incised up to 1500 m into bedrock, and its base lies 1200–1500 m below sea level for at least 70 km inland. Center-line ice thickness along most of the channel is about 2500 m, or about 2.5 times that of the surrounding ice sheet. This prominent bedrock trough was not apparent in existing radio-echo-sounding data. Reflection coefficients indicate that much of the basal interface is probably underlain by compacted, non-deforming sediment. The large ice thickness, coupled with relatively steep surface slopes, leads to high basal shear stresses (200–300 k Pa) along the ice stream. The large shear stresses and lack of a deformable bed imply that internal deformation plays a dominant role in the dynamics of Jakobshavns Isbræ.

Integrating satellite observations with modelling: basal shear stress of the Filcher-Ronne ice streams, Antarctica

2006 ◽  
Vol 364 (1844) ◽  
pp. 1795-1814 ◽  
Author(s):  
Ian Joughin ◽  
Jonathan L Bamber ◽  
Ted Scambos ◽  
Slawek Tulaczyk ◽  
Mark Fahnestock ◽  
...  
Keyword(s):  
Shear Stress ◽  
Ice Sheet ◽  
Inverse Methods ◽  
Satellite Observations ◽  
Major Influence ◽  
Ice Streams ◽  
Ice Stream ◽  
Subglacial Topography ◽  
Basal Shear ◽  
Thickness Measurements

Using inverse methods constrained by recent satellite observations, we have produced a comprehensive estimate of the basal shear stress beneath the Filchner-Ronne ice streams. The inversions indicate that a weak bed (approx. 4–20 kPa) underlies much of these ice streams. Compared to the Ross ice streams, the distribution of weak subglacial till is more heterogeneous, with ‘sticky spots’ providing much of the resistance to flow. A weak bed beneath Recovery ice stream extends several hundred kilometres inland with flow. Along this ice stream, discrepancies between thickness measurements and flux estimates suggest the existence of a deep (−1400 m) trough not resolved by existing maps of subglacial topography. We hypothesize that the presence of this and other deep troughs is a major influence on this sector of the ice sheet that is not fully incorporated in current models of ice-sheet evolution.

scholarly journals Seismic-reflection evidence for a deep subglacial trough beneath Jakobshavns Isbræ, West Greenland

1996 ◽  
Vol 42 (141) ◽  
pp. 219-232 ◽  
Author(s):  
Ted S. Clarke ◽  
Keiih Echelmeyer
Keyword(s):  
Seismic Reflection ◽  
Dominant Role ◽  
Ice Thickness ◽  
Shear Stresses ◽  
Outlet Glacier ◽  
West Greenland ◽  
Ice Stream ◽  
Surface Slopes ◽  
Radio Echo Sounding ◽  
Basal Shear

AbstractSeismic-reflection methods were used to determine the ice thickness and basal topography of Jakobshavns Isbræ, a large, fast-moving ice stream/outlet glacier in West Greenland. A method of data analysis was developed which involves the pointwise migration of data from a linear seismic array and a single explosive source; the method yields the depth, horizontal position and slope of the basal reflector. A deep U-shaped subglacial trough was found beneath the entire length of the well-defined ice stream. The trough is incised up to 1500 m into bedrock, and its base lies 1200–1500 m below sea level for at least 70 km inland. Center-line ice thickness along most of the channel is about 2500 m, or about 2.5 times that of the surrounding ice sheet. This prominent bedrock trough was not apparent in existing radio-echo-sounding data. Reflection coefficients indicate that much of the basal interface is probably underlain by compacted, non-deforming sediment. The large ice thickness, coupled with relatively steep surface slopes, leads to high basal shear stresses (200–300 k Pa) along the ice stream. The large shear stresses and lack of a deformable bed imply that internal deformation plays a dominant role in the dynamics of Jakobshavns Isbræ.

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 Glaciodynamic context of subglacial bedform generation and preservation

1999 ◽  
Vol 28 ◽  
pp. 23-32 ◽  
Author(s):  
Chris D. Clark
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Shear Stresses ◽  
Morphometric Characteristics ◽  
Glacial Cycle ◽  
Sheet Flow ◽  
Ice Flow ◽  
Ice Stream ◽  
Highly Sensitive ◽  
Basal Shear

AbstractSubglacially-produced drift lineations provide spatially extensive evidence of ice flow that can be used to aid reconstructions of the evolution of former ice sheets. Such reconstructions, however, are highly sensitive to assumptions made about the glaciodynamic context of lineament generation; when during the glacial cycle and where within the ice sheet were they produced. A range of glaciodynamic contexts are explored which include: sheet-flow submarginally restricted; sheet-flow pervasive; sheet- flow patch; ice stream; and surge or re-advance. Examples of each are provided. The crux of deciphering the appropriate context is whether lineations were laid down time-trans-gressively or isochronously. It is proposed that spatial and morphometric characteristics of lineations, and their association with other landforms, can be used as objective criteria to help distinguish between these cases.A logically complete ice-sheet reconstruction must also account for the observed patches of older lineations and other relict surfaces and deposits that have survived erasure by subsequent ice flow. A range of potential preservation mechanisms are explored, including: cold- based ice; low basal-shear stresses; shallowing of the deforming layer; and basal uncoupling.

scholarly journals Radar studies at the mouths of ice streams D and E, Antarctica

1993 ◽  
Vol 17 ◽  
pp. 262-268 ◽  
Author(s):  
Robert W. Jacobel ◽  
Robert Bindschadler
Keyword(s):  
Climate Change ◽  
Surface Topography ◽  
Satellite Imagery ◽  
Ice Thickness ◽  
West Antarctica ◽  
Ice Streams ◽  
The West ◽  
Mass Balance Calculation ◽  
Grounding Line ◽  
Thickness Measurements

Ice thickness measurements have been carried out at the mouths of ice streams D and E, West Antarctica using a surface-based impulse radar. These studies have been undertaken as a part of the continuing effort to understand the state of the West Antarctica ice sheet and its response to climate change. Thickness measurements will be used in the mass balance calculation currently in progress and to better understand features in the surface topography seen at low angle sun illumination in the satellite imagery. Results show that the discharge areas of ice streams D and E are thickening by approximately 1 m per year, and thus that these ice streams are probably loosing mass. Aperiodic wavelike features in the surface topography are described which pose interesting questions about migration of the grounding line and ice-stream dynamics.

scholarly journals Thinning and Grounding-Line Retreat on Ross Ice Shelf, Antarctica

1988 ◽  
Vol 11 ◽  
pp. 165-172 ◽  
Author(s):  
R. H. Thomas ◽  
S. N. Stephenson ◽  
R. A. Bindschadler ◽  
S. Shabtaie ◽  
C. R. Bentley
Keyword(s):  
Snow Accumulation ◽  
Gravity Potential ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Major Activity ◽  
Ice Stream ◽  
Grounding Line ◽  
Ice Stream B ◽  
Basal Melting

Detailed measurements of surface topography, ice motion, snow accumulation, and ice thickness were made in January 1974 and again in December 1984, along an 8 km stake network extending from the ice sheet, across the grounding line, and on to floating ice shelf in the mouth of slow-moving Ice Stream C, which flows into the eastern side of Ross Ice Shelf, Antarctica. During the 11 years between surveys, the grounding line retreated by approximately 300 m. This was caused by net thinning of the ice shelf, which we believe to be a response to the comparatively recent, major decrease in ice discharge from Ice Stream C. Farther inland, snow accumulation is not balanced by ice discharge, and the ice stream is growing progressively thicker.There is evidence that the adjacent Ice Stream B has slowed significantly over the last decade, and this may be an early indication that this fast-moving ice stream is about to enter a period of stagnation similar to that of Ice Stream C. Indeed, these large ice streams flowing from West Antarctica into Ross Ice Shelf may oscillate between periods of relative stagnation and major activity. During active periods, large areas of ice shelf thicken and run aground on seabed to form extensive “ice plains” in the mouth of the ice stream. Ultimately, these become too large to be pushed seaward by the ice stream, which then slows down and enters a period of stagnation. During this period, the grounding line of the ice plain retreats, as we observe today in the mouth of Ice Stream C, because nearby ice shelf, no longer compressed by ice-stream motion, progressively thins. At the same time, water within the deformable till beneath the ice starts to freeze on to the base of the ice stream, and snow accumulation progressively increases the ice thickness. A new phase of activity would be initiated when the increasing gravity potential of the ice stream exceeds the total resistance of the shrinking ice plain and the thinning layer of deformable till at the bed. This could occur rapidly if the effects of the shrinking ice plain outweigh those of the thinning (and therefore stiffening) till. Otherwise, the till layer would finally become completely frozen, and the ice stream would have to thicken sufficiently to initiate significant heating by internal deformation, followed by basal melting and finally saturation of an adequate thickness of till; this could take some thousands of years.

scholarly journals Ice-Flow and Thickness Measurements in the Sør-Rondane, Dronning Maud Land, Antarctica

1966 ◽  
Vol 6 (43) ◽  
pp. 69-81
Author(s):  
T. Van Autenboer ◽  
K. V. Blaiklock
Keyword(s):  
Aerial Photographs ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Gravity Station ◽  
Close Relationship ◽  
Dronning Maud Land ◽  
Subglacial Topography ◽  
Glacier Flow ◽  
The Antarctic ◽  
Thickness Measurements

AbstractVelocity and ice-thickness profiles were measured un the western glaciers of the Sør-Rondane during the Expéditions Antarctiques Belges of 1959 and 1960 Some of the stations were re-occupied for velocity measurements during the Expédition Antarctique Belgo-Néerlandaise, Campagne d’Été 1964–65.The profiles, with stations at 1 mile. (1.6 km.) intervals, were generally east-west and at right-angles to the direction of flow of the plateau outlet glaciers. The movement was measured by resection of each station from the main triangulation points over periods ranging from 256 to 1,501 days. Double ties with a Worden geodetic-type gravity meter were measured between the stations. An additional gravity station was occupied on rock at each end of the profile. The ice thickness and the subglacial topography are calculated from the gravity profiles. Combined with the surface velocity, they allow an estimate of the discharge of the glacier. The results indicate a close relationship between the glacier flow and the supply from the Antarctic Ice Sheet, as demonstrated by a study of the aerial photographs.

scholarly journals The use of tiltmeters to study the dynamics of Antarctic ice-shelf grounding lines

1991 ◽  
Vol 37 (125) ◽  
pp. 51-58 ◽  
Author(s):  
A. M. Smith
Keyword(s):  
Elastic Beam ◽  
Ice Thickness ◽  
Elastic Model ◽  
Beam Model ◽  
Line Position ◽  
Stream Data ◽  
Ice Shelf ◽  
Ice Stream ◽  
Grounding Line ◽  
Data Coverage

Abstract New tiltmeter data are presented from Doake Ice Rumples on Ronne Ice Shelf, Antarctica. Five sites which showed a tidal ice-shelf flexure have been analysed using an elastic beam model to investigate the variation of flexure amplitude with distance from the grounding line. An earlier study on Rutford Ice Stream which also used an elastic model required an ice thickness much less than that observed. Reworking the Rutford Ice Stream data suggests that this greatly reduced ice thickness is not required, given the current sparse data coverage. The elastic model is used to improve the estimated grounding-line position on Rutford Ice Stream. Some of the difficulties in modelling ice-shelf flexure and locating grounding lines are discussed.

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