scholarly journals Mass–Balance and Ice–Flow–Law Parameters for East Antarctica

1985 ◽  
Vol 31 (109) ◽  
pp. 334-339 ◽  
Author(s):  
T.C Hamley ◽  
I.N. Smith ◽  
N.W. Young
Keyword(s):  
Power Flow ◽  
Grid Point ◽  
Ice Sheet ◽  
Field Measurements ◽  
East Antarctica ◽  
Surface Velocity ◽  
Shear Strain Rate ◽  
Polar Research Institute ◽  
Flow Law ◽  
Basal Shear

AbstractA comprehensive set of ice-velocity and thickness data from traverses within the IAGP study area (bounded by long. 90°E. and 135°E., and north of lat. 80°S.) is compared with steady-state mass-flux calculations based on Scott Polar Research Institute (SPRI) map compilations.The results of previous regional mass-budget estimates are reviewed and followed by a description of the new field measurements and the basis upon which a computer “grid–point” program is used to calculate balance fluxes.A comparison of measured and balance fluxes indicates that the ice sheet in this region of East Antarctica is unlikely to be significantly out of balance.The ratio of average column to surface velocity is discussed and calculated to be 0.89.An analysis of the mean shear strain-rate (VS/Z), versus down-slope basal shear stress (τb=ρgᾱZ), suggests that power flow-law parameters ofn= 3.21 andk= 0.023 bar−nm−1are appropriate for the effective basal shear zone in this region of the Antarctic ice sheet.

scholarly journals Mass–Balance and Ice–Flow–Law Parameters for East Antarctica

1985 ◽  
Vol 31 (109) ◽  
pp. 334-339 ◽  
Author(s):  
T.C Hamley ◽  
I.N. Smith ◽  
N.W. Young
Keyword(s):  
Power Flow ◽  
Grid Point ◽  
Ice Sheet ◽  
Field Measurements ◽  
East Antarctica ◽  
Surface Velocity ◽  
Shear Strain Rate ◽  
Polar Research Institute ◽  
Flow Law ◽  
Basal Shear

AbstractA comprehensive set of ice-velocity and thickness data from traverses within the IAGP study area (bounded by long. 90°E. and 135°E., and north of lat. 80°S.) is compared with steady-state mass-flux calculations based on Scott Polar Research Institute (SPRI) map compilations.The results of previous regional mass-budget estimates are reviewed and followed by a description of the new field measurements and the basis upon which a computer “grid–point” program is used to calculate balance fluxes.A comparison of measured and balance fluxes indicates that the ice sheet in this region of East Antarctica is unlikely to be significantly out of balance.The ratio of average column to surface velocity is discussed and calculated to be 0.89.An analysis of the mean shear strain-rate (VS/Z), versus down-slope basal shear stress (τb = ρgᾱZ), suggests that power flow-law parameters of n = 3.21 and k = 0.023 bar−n m−1 are appropriate for the effective basal shear zone in this region of the Antarctic ice sheet.

scholarly journals Basal Water Film, Basal Water Pressure, and Velocity of Traveling Waves on Glaciers

1983 ◽  
Vol 29 (101) ◽  
pp. 20-27 ◽  
Author(s):  
J. Weertman ◽  
G. E. Birchfield
Keyword(s):  
Traveling Waves ◽  
Traveling Wave ◽  
Water Pressure ◽  
Strong Support ◽  
Water Film ◽  
Field Measurements ◽  
Surface Velocity ◽  
Sliding Velocity ◽  
Wave Velocities ◽  
Basal Shear

Abstract The theory of Nye and of Weertman of traveling waves on glaciers is extended to cover the situation where the presence of abundant basal water or increased basal water pressure produces increased sliding of a glacier over its bed. It is found that the ratio of traveling-wave velocity to surface velocity is independent of the amount of water or the basal water pressure. The theoretical value of this ratio, about 4 to 5, agrees with that found in field measurements (the most recent data are from Mer de Glace). It is concluded that field observations of traveling-wave velocities lend strong support to any glacier sliding theory in which the sliding velocity is proportional to the basal shear stress raised to about a second to fifth power and in which the sliding velocity is a function of either or both the amount of water at the bed of a glacier and the pressure within this water.

An inventory of Antarctic sub-glacial lakes

1996 ◽  
Vol 8 (3) ◽  
pp. 281-286 ◽  
Author(s):  
M.J. Siegert ◽  
J.A. Dowdeswell ◽  
M.R. Gorman ◽  
N.F. McIntyre
Keyword(s):  
Ice Sheet ◽  
East Antarctica ◽  
Glacial Lake ◽  
Ice Thickness ◽  
Minimum Length ◽  
Glacial Lakes ◽  
University Of Cambridge ◽  
Radio Echo Sounding ◽  
Polar Research Institute ◽  
Lake Type

An extensive analogue database of 60 MHz radio-echo sounding records of Antarctica (covering 50% of the ice sheet) is held at the Scott Polar Research Institute, University of Cambridge. This database was analysed in order to determine the presence and location of Antarctic sub-glacial lakes. In total, 77 sub-glacial lake-type records were identified, 13 more than detected in previous studies. An inventory of these sub-glacial lakes includes geographical coordinates, minimum length and overlying ice thickness for each lake. Information concerning the location of these lakes indicates that the majority (~70%) are found in the proximity of ice divides at Dome C and Ridge B within East Antarctica.

scholarly journals Modelling of anisotropic ice flow in Law Dome, East Antarctica

1999 ◽  
Vol 29 ◽  
pp. 184-190 ◽  
Author(s):  
W. L.Wang ◽  
Roland C. Warner
Keyword(s):  
Shear Strain ◽  
Ice Sheet ◽  
East Antarctica ◽  
Shear Strain Rate ◽  
Ice Flow ◽  
Anisotropic Flow ◽  
Ice Cap ◽  
Model Predictions ◽  
Flow Enhancement ◽  
Good Agreement

AbstractA model for ice flow in a polar ice sheet is presented. It is based on laboratory measurements of ice rheology, and includes the effect of anisotropic-flow enhancement in tertiary creep as the ice progresses through a range of stress regimes as it passes through the ice sheet. This flow model is applied to the transect from the summit of Law Dome, East Antarctica, to Gape Folger. In the upper layers of the ice sheet good agreement is found between the shear strain-rate profiles from the model and borehole-inclination measurements. Modifications of the simple model predictions for high shear strain rates in the lower layers of the ice cap are required in order to match the observed surface velocities. In these lower regions reductions in both the enhancement of shear flow and shear stress appear to be required, and this suggests that more attention needs to be given to the dynaimcs deep within ice sheets.

scholarly journals Simulation of the influence of ice rheology on velocity profiles and ice-sheet mass balance

1998 ◽  
Vol 27 ◽  
pp. 194-200 ◽  
Author(s):  
W. L. Wang ◽  
Roland C. Warner
Keyword(s):  
Velocity Profile ◽  
Shear Strain ◽  
Accurate Determination ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
Surface Velocity ◽  
Shear Strain Rate ◽  
Ice Crystal ◽  
Current State ◽  
Rate Profile

Assessment of the effect of the Antarctic ice sheet on sea level requires an accurate determination of its current state of balance. This is usually done by comparing the ice net accumulation for an area with the net outward flow of the ice. To obtain the net outward flux to better than 20% accuracy the relationship between the column-integrated ice flux and measurements of ice-sheet thickness and surface velocity must be considered. That relationship is summarised by the ratio of depth-averaged velocity ϒ to surface velocity γs in areas where ice sliding can be neglected, this ratio strongly reflects the rheological properties of the ice and depends on the shear strain-rate profile through the ice column, which is influenced by profiles of stress, temperature and ice-crystal fabric. We present calculations from a flowline model of a hypothetical large ice sheet to demonstrate how development of an anisotropic ice-crystal fabric can influence the depth profile of horizontal velocity. The temperature dependence of ice rheology, combined with typical ice-sheet temperature profiles, yields a more block-like velocity profile with increasing to values in the range 0.89-0.96 from the isothermal rheology value of 0.8. Our results show that the onset of enhanced shear flow with increasing shear strain, as a consequence of anisotropy, and then a reduction of enhancement nearer the bedrock, can modify the velocity profile, giving values typically in the range 0.86-0.91. Smaller values than these may also occur for rougher bedrock or thinner ice.

scholarly journals Reconstruction and Disintegration of Ice Sheets for the Climap 18000 and 125000 Years B.P. Experiments: Theory

1979 ◽  
Vol 24 (90) ◽  
pp. 493-495
Author(s):  
T. J. Hughes
Keyword(s):  
Shear Stress ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Frictional Heat ◽  
Ice Streams ◽  
Ice Stream ◽  
Grounding Line ◽  
Flow Law ◽  
Basal Shear ◽  
Stress Variations

AbstractSize, shape, and surface albedo of former ice sheets are needed in order to model atmospheric circulation for the CLIMAP 18000 years B.P. experiment. Both the size and shape of an ice sheet depend on the hardness of ice and its coupling to bedrock. Ice hardness is controlled by ice temperature and fabric, which are not adequately described by any ice flow law. Ice–bed coupling is controlled by bed roughness and basal melt water, which are not adequately described by any ice sliding law. With these inadequacies in mind, we assumed equilibrium ice-sheet conditions 18000 years ago and combined the standard steady-state flow and sliding laws of ice with the equation of mass balance to obtain separate basal shear-stress variations along ice-sheet flow lines for a frozen bed when the flow law dominates and for a melted bed when the sliding law dominates. Theoretical basal shear-stress variations were then derived for freezing and melting beds on the assumption that separate melted areas of the bed had water films of constant thickness which expanded and merged for a melting bed but contracted and separated for a freezing bed. Theoretical basal shear-stress variations were also derived for ice streams along marine ice-sheet margins and ice lobes along terrestrial ice-sheet margins on the assumption that the entire area of their bed was wet so that further melting increased the water-layer thickness, which would then be decreased by freezing. Melting was assumed to continue to the grounding line of an ice stream and the minimum-slope surface inflection line of an ice lobe, where freezing began and continued to the ice-lobe terminus. Ice–bed uncoupling is complete at an ice-stream grounding line and maximized at an ice-lobe minimum-slope inflection line, so ice velocity and consequent generation of frictional heat were assumed to reach maxima across these lines. Theoretical basal shear-stress variations were derived for the zone of converging flow at the heads of ice streams and ice lobes, and from domes to saddles along the ice divide for both frozen and melted beds.

scholarly journals Reconstruction and Disintegration of Ice Sheets for the Climap 18000 and 125000 Years B.P. Experiments: Theory

1979 ◽  
Vol 24 (90) ◽  
pp. 493-495 ◽  
Author(s):  
T. J. Hughes
Keyword(s):  
Shear Stress ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Frictional Heat ◽  
Ice Streams ◽  
Ice Stream ◽  
Grounding Line ◽  
Flow Law ◽  
Basal Shear ◽  
Stress Variations

Abstract Size, shape, and surface albedo of former ice sheets are needed in order to model atmospheric circulation for the CLIMAP 18000 years B.P. experiment. Both the size and shape of an ice sheet depend on the hardness of ice and its coupling to bedrock. Ice hardness is controlled by ice temperature and fabric, which are not adequately described by any ice flow law. Ice–bed coupling is controlled by bed roughness and basal melt water, which are not adequately described by any ice sliding law. With these inadequacies in mind, we assumed equilibrium ice-sheet conditions 18000 years ago and combined the standard steady-state flow and sliding laws of ice with the equation of mass balance to obtain separate basal shear-stress variations along ice-sheet flow lines for a frozen bed when the flow law dominates and for a melted bed when the sliding law dominates. Theoretical basal shear-stress variations were then derived for freezing and melting beds on the assumption that separate melted areas of the bed had water films of constant thickness which expanded and merged for a melting bed but contracted and separated for a freezing bed. Theoretical basal shear-stress variations were also derived for ice streams along marine ice-sheet margins and ice lobes along terrestrial ice-sheet margins on the assumption that the entire area of their bed was wet so that further melting increased the water-layer thickness, which would then be decreased by freezing. Melting was assumed to continue to the grounding line of an ice stream and the minimum-slope surface inflection line of an ice lobe, where freezing began and continued to the ice-lobe terminus. Ice–bed uncoupling is complete at an ice-stream grounding line and maximized at an ice-lobe minimum-slope inflection line, so ice velocity and consequent generation of frictional heat were assumed to reach maxima across these lines. Theoretical basal shear-stress variations were derived for the zone of converging flow at the heads of ice streams and ice lobes, and from domes to saddles along the ice divide for both frozen and melted beds.

scholarly journals Basal Water Film, Basal Water Pressure, and Velocity of Traveling Waves on Glaciers

1983 ◽  
Vol 29 (101) ◽  
pp. 20-27 ◽  
Author(s):  
J. Weertman ◽  
G. E. Birchfield
Keyword(s):  
Traveling Waves ◽  
Traveling Wave ◽  
Water Pressure ◽  
Strong Support ◽  
Water Film ◽  
Field Measurements ◽  
Surface Velocity ◽  
Sliding Velocity ◽  
Wave Velocities ◽  
Basal Shear

AbstractThe theory of Nye and of Weertman of traveling waves on glaciers is extended to cover the situation where the presence of abundant basal water or increased basal water pressure produces increased sliding of a glacier over its bed. It is found that the ratio of traveling-wave velocity to surface velocity is independent of the amount of water or the basal water pressure. The theoretical value of this ratio, about 4 to 5, agrees with that found in field measurements (the most recent data are from Mer de Glace). It is concluded that field observations of traveling-wave velocities lend strong support to any glacier sliding theory in which the sliding velocity is proportional to the basal shear stress raised to about a second to fifth power and in which the sliding velocity is a function of either or both the amount of water at the bed of a glacier and the pressure within this water.

scholarly journals Ice-flow properties at Dome Summit South, Law Dome, East Antarctica

2002 ◽  
Vol 35 ◽  
pp. 567-573 ◽  
Author(s):  
Weili Wang ◽  
Roland C. Warner ◽  
William F. Budd
Keyword(s):  
Shear Strain ◽  
Ice Core ◽  
Ice Sheet ◽  
East Antarctica ◽  
Shear Strain Rate ◽  
Flow Properties ◽  
Ice Flow ◽  
Antarctic Research ◽  
Flow Enhancement ◽  
Rate Profile

AbstractIce-flow properties within a polar ice sheet are examined using the comprehensive data gathered from ice-core drilling by Australian National Antarctic Research Expeditions (ANARE) at Dome Summit South (DSS), on Law Dome, East Antarctica. Using the shear strain rates derived from borehole inclination measurements we demonstrate the need to modify the ice-flow relations to treat enhanced shear deformation deep within the ice sheet. We show that the relation between enhanced flow and the measured crystallographic properties is generally in accord with expectations, at least in the upper parts of the ice sheet, but it becomes clear that nearer to the bedrock the situation is more complicated. We also compare the observed shear strain-rate profile with results from a model that describes flow enhancement as a function of the applied stresses.

Satellite Altimeter Results Over East Antarctica

1982 ◽  
Vol 3 ◽  
pp. 32-35 ◽  
Author(s):  
R. L. Brooks
Keyword(s):  
Tracking System ◽  
Ice Sheet ◽  
East Antarctica ◽  
Satellite Altimeter ◽  
Ice Shelves ◽  
Ice Surface ◽  
Operational Lifetime ◽  
Waveform Retracking ◽  
Better Than

During the operational lifetime of the Seasat altimeter from 3 July to 10 October 1978, more than 450 overflights were made over East Antarctica inland to latitude 72°S. An analysis of selected passes over a variety of ice features demonstrates that the oceanographic altimeter performed surprisingly well over the ice sheet and ice shelves, acquiring useful measurements during approximately 70% of each pass. The altimeter's onboard tracking system dampened out the ice-surface elevations, but post-flight retracking of the stored return waveforms reveals excellent ice-surface details. After waveform retracking, the altimeter repeatability is better than ±1 m.

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