scholarly journals Ice Flow Leading to the Deep Core Hole at Dye 3, Greenland

1984 ◽  
Vol 5 ◽  
pp. 185-190 ◽  
Author(s):  
I. M. Whillans ◽  
K. C. Jezek ◽  
A. R. Drew ◽  
N. Gundestrup
Keyword(s):  
Flow Line ◽  
Surface Velocity ◽  
Surface Pattern ◽  
Ice Thickness ◽  
Surface Slope ◽  
Core Hole ◽  
Lateral Velocity ◽  
Ice Flow ◽  
The Core ◽  
Surface Ice

Detailed studies of the last 20 km of the flow-line leading to the core hole at Dye 3 Greenland, provide a description of ice flow over and around basal hills. The surface pattern is very simple. Velocity vectors are nearly parallel to one another and the largest variations in velocity are speed changes along the direction of flow. The surface elevation is stepped and the speed is faster than average where the surface slope is steepest. These positions correspond to basal highs, and the surface velocity increases as expected, based on the decrease in ice thickness, which indicates that most of the ice thickness must vary in velocity as does surface ice. Further support for this comes from the form of an internal radio-reflecting layer, which, in general, has the same shape as the bed but with much reduced relief. The damping of the relief is the same both along and across the flowline, suggesting that lateral velocity fluctuations are not important and that flow around and between obstacles is not well developed at the surface or at depth. At two sites, however, the internal layer does not match the bed and at one of these there must be important third-dimensional flow at depth.

scholarly journals Ice Flow Leading to the Deep Core Hole at Dye 3, Greenland

1984 ◽  
Vol 5 ◽  
pp. 185-190 ◽  
Author(s):  
I. M. Whillans ◽  
K. C. Jezek ◽  
A. R. Drew ◽  
N. Gundestrup
Keyword(s):  
Flow Line ◽  
Surface Velocity ◽  
Surface Pattern ◽  
Ice Thickness ◽  
Surface Slope ◽  
Core Hole ◽  
Lateral Velocity ◽  
Ice Flow ◽  
The Core ◽  
Surface Ice

Detailed studies of the last 20 km of the flow-line leading to the core hole at Dye 3 Greenland, provide a description of ice flow over and around basal hills. The surface pattern is very simple. Velocity vectors are nearly parallel to one another and the largest variations in velocity are speed changes along the direction of flow. The surface elevation is stepped and the speed is faster than average where the surface slope is steepest. These positions correspond to basal highs, and the surface velocity increases as expected, based on the decrease in ice thickness, which indicates that most of the ice thickness must vary in velocity as does surface ice. Further support for this comes from the form of an internal radio-reflecting layer, which, in general, has the same shape as the bed but with much reduced relief. The damping of the relief is the same both along and across the flowline, suggesting that lateral velocity fluctuations are not important and that flow around and between obstacles is not well developed at the surface or at depth. At two sites, however, the internal layer does not match the bed and at one of these there must be important third-dimensional flow at depth.

scholarly journals Ice Flow Along AN Iagp Flow Line, Wilkes Land, Antarctica (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 346 ◽  
Author(s):  
N.W. Young ◽  
D. SheehY ◽  
T. Hamley
Keyword(s):  
Strain Rate ◽  
Large Scale ◽  
Flow Line ◽  
Accumulation Rate ◽  
Surface Profile ◽  
Ice Thickness ◽  
Shear Strain Rate ◽  
Surface Slope ◽  
Ice Flow ◽  
Wilkes Land

Trilateration and single line surveys have been made to about 900 km inland of Casey, Wilkes Land, to measure surface elevation, ice thickness, horizontal velocity, and other parameters. On the large scale the velocity U increases smoothly from 8 m a−1, 800 km inland, to 280 m a−1 inland of the fast outlet streams. This increase in velocity is associated with a corresponding increase in the large-scale smoothed (over about 30 ice thicknesses) basal shear stress τb from 0.4 to 1.5 bar. The mean shear strain-rate through the ice sheet U/Z = kτb4 , where Z is the ice thickness (range 4 500 to 1 700 m). At scales of one to several ice thicknesses large variations occur in surface slope and ice thickness without proportionally large velocity variations, because of the effect of the longitudinal stress. Detailed measurements made over a 30 km section indicated that the surface longitudinal strain-rate gradient varied from -1.7 to +1.3×l0−6 a−1 m−1 along with variations in surface slope of from -3.5 to +1.5%. A multilayer model, based on the solution of the biharmonic equation for the stream function, was used in a study of the ice flow associated with these surface undulations. Given the bedrock topography and large-scale flow parameters, the model closely predicted the measured surface profile when the variation of the surface accumulation rate over an undulation was also considered.

scholarly journals A Bayesian ice thickness estimation model for large-scale applications

2019 ◽  
Vol 66 (255) ◽  
pp. 137-152
Author(s):  
Mauro A. Werder ◽  
Matthias Huss ◽  
Frank Paul ◽  
Amaury Dehecq ◽  
Daniel Farinotti
Keyword(s):  
Large Scale ◽  
Flow Line ◽  
Forward Model ◽  
Ice Thickness ◽  
Estimation Model ◽  
Mountain Glacier ◽  
Ice Flow ◽  
Thickness Estimation ◽  
Surface Ice ◽  
Thickness Measurements

AbstractAccurate estimations of ice thickness and volume are indispensable for ice flow modelling, hydrological forecasts and sea-level rise projections. We present a new ice thickness estimation model based on a mass-conserving forward model and a Bayesian inversion scheme. The forward model calculates flux in an elevation-band flow-line model, and translates this into ice thickness and surface ice speed using a shallow ice formulation. Both ice thickness and speed are then extrapolated to the map plane. The model assimilates observations of ice thickness and speed using a Bayesian scheme implemented with a Markov chain Monte Carlo method, which calculates estimates of ice thickness and their error. We illustrate the model's capabilities by applying it to a mountain glacier, validate the model using 733 glaciers from four regions with ice thickness measurements, and demonstrate that the model can be used for large-scale studies by fitting it to over 30 000 glaciers from five regions. The results show that the model performs best when a few thickness observations are available; that the proposed scheme by which parameter-knowledge from a set of glaciers is transferred to others works but has room for improvements; and that the inferred regional ice volumes are consistent with recent estimates.

BITE, the Bayesian Ice Thickness Estimation model

2020 ◽  
Author(s):  
Mauro Werder ◽  
Matthias Huss ◽  
Frank Paul ◽  
Amaury Dehecq ◽  
Daniel Farinotti
Keyword(s):  
Large Scale ◽  
Flow Line ◽  
Forward Model ◽  
Ice Thickness ◽  
Estimation Model ◽  
Mountain Glacier ◽  
Ice Flow ◽  
Thickness Estimation ◽  
Surface Ice ◽  
Thickness Measurements

<p>Accurate estimations of ice thickness and volume are indispensable for ice flow modelling, hydrological forecasts and sea-level rise projections. We present BITE, a new ice thickness estimation model based on a mass-conserving forward model and a Bayesian inversion scheme. The forward model calculates flux in an elevation-band flow-line model, and translates this into ice thickness and surface ice speed using a shallow ice formulation. Both ice thickness and speed are then extrapolated to the map plane. The model assimilates observations of ice thickness and speed using a Bayesian scheme implemented with a Markov chain Monte Carlo method, which calculates estimates of ice thickness and their error. We illustrate the model's capabilities by applying it to a mountain glacier, validate the model using 733 glaciers from four regions with ice thickness measurements, and demonstrate that the model can be used for large-scale studies by fitting it to over 30 000 glaciers from five regions. The results show that the model performs best when a few thickness observations are available; that the proposed scheme by which parameter-knowledge from a set of glaciers is transferred to others works but has room for improvements; and that the inferred regional ice volumes are consistent with recent estimates.</p>

scholarly journals Ice Flow Along AN Iagp Flow Line, Wilkes Land, Antarctica (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 346-346
Author(s):  
N.W. Young ◽  
D. SheehY ◽  
T. Hamley
Keyword(s):  
Strain Rate ◽  
Large Scale ◽  
Flow Line ◽  
Accumulation Rate ◽  
Surface Profile ◽  
Ice Thickness ◽  
Shear Strain Rate ◽  
Surface Slope ◽  
Ice Flow ◽  
Wilkes Land

Trilateration and single line surveys have been made to about 900 km inland of Casey, Wilkes Land, to measure surface elevation, ice thickness, horizontal velocity, and other parameters. On the large scale the velocity U increases smoothly from 8 m a−1, 800 km inland, to 280 m a−1 inland of the fast outlet streams. This increase in velocity is associated with a corresponding increase in the large-scale smoothed (over about 30 ice thicknesses) basal shear stress τb from 0.4 to 1.5 bar. The mean shear strain-rate through the ice sheet U/Z = kτb4, where Z is the ice thickness (range 4 500 to 1 700 m).At scales of one to several ice thicknesses large variations occur in surface slope and ice thickness without proportionally large velocity variations, because of the effect of the longitudinal stress. Detailed measurements made over a 30 km section indicated that the surface longitudinal strain-rate gradient varied from -1.7 to +1.3×l0−6 a−1 m−1 along with variations in surface slope of from -3.5 to +1.5%.A multilayer model, based on the solution of the biharmonic equation for the stream function, was used in a study of the ice flow associated with these surface undulations. Given the bedrock topography and large-scale flow parameters, the model closely predicted the measured surface profile when the variation of the surface accumulation rate over an undulation was also considered.

scholarly journals Are longitudinal ice-surface structures on the Antarctic Ice Sheet indicators of long-term ice-flow configuration?

2014 ◽  
Vol 2 (2) ◽  
pp. 911-933 ◽  
Author(s):  
N. F. Glasser ◽  
S. J. A. Jennings ◽  
M. J. Hambrey ◽  
B. Hubbard
Keyword(s):  
Flow Line ◽  
Ice Sheet ◽  
Surface Structures ◽  
Surface Velocity ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Ice Surface ◽  
Ice Stream ◽  
The Antarctic

Abstract. Continent-wide mapping of longitudinal ice-surface structures on the Antarctic Ice Sheet reveals that they originate in the interior of the ice sheet and are arranged in arborescent networks fed by multiple tributaries. Longitudinal ice-surface structures can be traced continuously down-ice for distances of up to 1200 km. They are co-located with fast-flowing glaciers and ice streams that are dominated by basal sliding rates above tens of m yr-1 and are strongly guided by subglacial topography. Longitudinal ice-surface structures dominate regions of converging flow, where ice flow is subject to non-coaxial strain and simple shear. Associating these structures with the AIS' surface velocity field reveals (i) ice residence times of ~ 2500 to 18 500 years, and (ii) undeformed flow-line sets for all major flow units analysed except the Kamb Ice Stream and the Institute and Möller Ice Stream areas. Although it is unclear how long it takes for these features to form and decay, we infer that the major ice-flow and ice-velocity configuration of the ice sheet may have remained largely unchanged for several thousand years, and possibly even since the end of the last glacial cycle. This conclusion has implications for our understanding of the long-term landscape evolution of Antarctica, including large-scale patterns of glacial erosion and deposition.

scholarly journals Flow of Blue Glacier, Olympic Mountains, Washington, U.S.A.

1974 ◽  
Vol 13 (68) ◽  
pp. 187-212 ◽  
Author(s):  
Mark F. Meier ◽  
W. Barclay Kamb ◽  
Clarence R. Allen ◽  
Robert P. Sharp
Keyword(s):  
Maximum Velocity ◽  
Ice Thickness ◽  
Center Line ◽  
Surface Slope ◽  
Channel Narrowing ◽  
Olympic Mountains ◽  
Principal Axes ◽  
Flow Effects ◽  
Surface Ice ◽  
Longitudinal Extension

Velocity and strain-rate patterns in a small temperate valley glacier display flow effects of channel geometry, ice thickness, surface slope, and ablation. Surface velocities of 20–55 m/year show year-to-year fluctuations of 1.5–3 m/year. Transverse profiles of velocity have the form of a higher-order parabola modified by the effects of flow around a broad bend in the channel, which makes the velocity profile asymmetric, with maximum velocity displaced toward the outside of the bend. Marginal sliding rates are 5–22 m/year against bedrock and nil against debris. Velocity vectors diverge from the glacier center-line near the terminus, in response to surface ice loss, but converge toward it near the firn line because of channel narrowing. Plunge of the vectors gives an emergence flow component that falls short of balancing ice loss by about 1 m/year. Center-line velocities vary systematically with ice thickness and surface slope. In the upper half of the reach studied, effects of changing thickness and slope tend to compensate, and velocities are nearly constant; in the lower half, the effects are cumulative and velocities decrease progressively down-stream. Where the slope increases down-stream from 7° to 9°, reflecting a bedrock step, there is localized longitudinal extension of 0.03 year–1followed by compression of 0.08 year–1where the slope decreases. Marginal shear (up to 0.5 year–1) is strongly asymmetric due to flow around the bend: the stress center-line, where one of the principal axes becomes longitudinal, is displaced 150 m toward the inside of the bend. This effect is prominently visible in the crevasse pattern. Ice fluxes calculated independently by “laminar” flow theory and by continuity disagree in a way which shows that internal deformation of the ice is controlled not by local surface slope but by an effective slope that is nearly constant over the reach studied.

scholarly journals Changes in the Behaviour of the Unteraargletscher in the Last 125 Years

1970 ◽  
Vol 9 (56) ◽  
pp. 195-212 ◽  
Author(s):  
R. Haefeli
Keyword(s):  
Marked Decrease ◽  
Decisive Role ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Surface Slope ◽  
Simple Method ◽  
Glacier Tongue ◽  
Slowing Down ◽  
Shear Component ◽  
Glacier Flow

All the measurements involved concern the glacier tongue between its end and 2 600 m a.s.l. The total loss of volume of the Unteraargletscher since its last maximum advance (1871) is estimated to be 2.4 km3, which corresponds to a mean surface lowering of 0.67 m/year (referred to a total glacierized area of c. 40 km2 on average). The considerable slowing down of the glacier flow velocity over the 125 years is primarily attributable to the marked decrease in the sliding component, whereas the shear component has only changed slightly. This behaviour is connected with the fact that the decrease in ice thickness has been accompanied by an increase in surface slope, so that the two effects on the shear component partially compensate each other. The seasonal variations in surface velocity were measured simultaneously at two profiles by Agassiz and his team in 1845/46. These variations are due to the variable amount of melt water and the resulting variations in hydrostatic pressure in the contact zone between ice and bedrock, in which the plastic contraction of the water channels plays a decisive role. This leads to the problem of water circulation in the interior of a glacier and its importance in the sliding process. Finally a simple method for the approximate calculation of the longitudinal profile of the surface of a glacier tongue in a steady state and with constant ablation is indicated.

scholarly journals Changes in the Behaviour of the Unteraargletscher in the Last 125 Years

1970 ◽  
Vol 9 (56) ◽  
pp. 195-212 ◽  
Author(s):  
R. Haefeli
Keyword(s):  
Marked Decrease ◽  
Decisive Role ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Surface Slope ◽  
Simple Method ◽  
Glacier Tongue ◽  
Slowing Down ◽  
Shear Component ◽  
Glacier Flow

All the measurements involved concern the glacier tongue between its end and 2 600 m a.s.l. The total loss of volume of the Unteraargletscher since its last maximum advance (1871) is estimated to be 2.4 km3, which corresponds to a mean surface lowering of 0.67 m/year (referred to a total glacierized area ofc. 40 km2on average). The considerable slowing down of the glacier flow velocity over the 125 years is primarily attributable to the marked decrease in the sliding component, whereas the shear component has only changed slightly. This behaviour is connected with the fact that the decrease in ice thickness has been accompanied by an increase in surface slope, so that the two effects on the shear component partially compensate each other. The seasonal variations in surface velocity were measured simultaneously at two profiles by Agassiz and his team in 1845/46. These variations are due to the variable amount of melt water and the resulting variations in hydrostatic pressure in the contact zone between ice and bedrock, in which the plastic contraction of the water channels plays a decisive role. This leads to the problem of water circulation in the interior of a glacier and its importance in the sliding process. Finally a simple method for the approximate calculation of the longitudinal profile of the surface of a glacier tongue in a steady state and with constant ablation is indicated.

scholarly journals The ice thickness distribution of Flask Glacier, Antarctic Peninsula, determined by combining radio-echo soundings, surface velocity data and flow modelling

2013 ◽  
Vol 54 (63) ◽  
pp. 18-24 ◽  
Author(s):  
Daniel Farinotti ◽  
Hugh Corr ◽  
G.Hilmar Gudmundsson
Keyword(s):  
Antarctic Peninsula ◽  
Thickness Distribution ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Volume ◽  
Flow Modelling ◽  
Bedrock Topography ◽  
Sparse Measurements

AbstractAn interpolated bedrock topography is presented for Flask Glacier, one of the tributaries of the remnant part of the Larsen B ice shelf, Antarctic Peninsula. The ice thickness distribution is derived by combining direct but sparse measurements from airborne radio-echo soundings with indirect estimates obtained from ice-flow modelling. The ice-flow model is applied to a series of transverse profiles, and a first estimate of the bedrock is iteratively adjusted until agreement between modelled and measured surface velocities is achieved. The adjusted bedrock is then used to reinterpret the radio-echo soundings, and the recovered information used to further improve the estimate of the bedrock itself. The ice flux along the glacier center line provides an additional and independent constraint on the ice thickness. The resulting bedrock topography reveals a glacier bed situated mainly below sea level with sections having retrograde slope. The total ice volume of 120 ±15 km3 for the considered area of 215 km2 corresponds to an average ice thickness of 560 ± 70 m.

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