scholarly journals The stability of a viscous till sheet coupled with ice flow, considered at wavelengths less than the ice thickness

1998 ◽  
Vol 44 (147) ◽  
pp. 285-292 ◽  
Author(s):  
Richard C. A. Hindmarsh
Keyword(s):  
Large Scale ◽  
Flow Instability ◽  
Ice Thickness ◽  
Ice Flow ◽  
Perturbation Amplitude ◽  
Sediment Flow ◽  
Viscous Models ◽  
The Stability ◽  
Parameter Ranges ◽  
Ice Sheet Modelling

AbstractA perturbation method is used to analyse the stability of a thin till layer overlain by a deep ice layer. Ice is modelled as a linearly viscous fluid, while the till viscosity has power-law dependence on stress and effective pressure. A linearized set of equations yields descriptions of the coupling of the ice flow with the sediment flow and reveals parameter ranges where the till-perturbation amplitude can grow. This sheet-flow instability is an essential part of any theory of drumlin formation and shows that viscous models of till have the ability to explain typical deforming-bed features. This is of great significance for large-scale ice-sheet modelling.

scholarly journals The stability of a viscous till sheet coupled with ice flow, considered at wavelengths less than the ice thickness

1998 ◽  
Vol 44 (147) ◽  
pp. 285-292 ◽  
Author(s):  
Richard C. A. Hindmarsh
Keyword(s):  
Large Scale ◽  
Flow Instability ◽  
Ice Thickness ◽  
Ice Flow ◽  
Perturbation Amplitude ◽  
Sediment Flow ◽  
Viscous Models ◽  
The Stability ◽  
Parameter Ranges ◽  
Ice Sheet Modelling

AbstractA perturbation method is used to analyse the stability of a thin till layer overlain by a deep ice layer. Ice is modelled as a linearly viscous fluid, while the till viscosity has power-law dependence on stress and effective pressure. A linearized set of equations yields descriptions of the coupling of the ice flow with the sediment flow and reveals parameter ranges where the till-perturbation amplitude can grow. This sheet-flow instability is an essential part of any theory of drumlin formation and shows that viscous models of till have the ability to explain typical deforming-bed features. This is of great significance for large-scale ice-sheet modelling.

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 Large-Scale Numerical Modelling of the Antarctic Ice Sheet

1982 ◽  
Vol 3 ◽  
pp. 42-49 ◽  
Author(s):  
W.F. Budd ◽  
I.N. Smith
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Accumulation Rate ◽  
Ice Sheet ◽  
Ice Thickness ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Flow Parameters ◽  
The Antarctic ◽  
Thinning Rate

A large-scale dynamic numerical model of the Antarctic ice sheet has been developed to study its present state of ice flow and mass balance as well as its response to long-term changes of climate or sea-level.The flow of ice over a two-dimensional grid is determined from the ice thickness, the basal shear stress, the bedrock depth, and ice flow parameters derived from velocities of existing ice sheets. The change in ice thickness with time is governed by the continuity equation involving the ice flux divergence and the ice accumulation or ablation. At the ice sheet seaward boundary, a floating criterion and floating ice thinning rate apply. Bedrock depression with a time-delayed response dependent on the history of the ice load is also included.A 61 × 61 point grid with 100 km spacing has been used to represent the ice-sheet surface, bedrock, and accumulation rate. The model has been used to simul a te the growth of the present ice sheet and i ts reaction to changes of sea-level, bedrock depression, accumulation rate, ice flow parameters, and the iceshelf thinning rate.Preliminary results suggest that the present ice sheet is not in equilibrium but rather is still adjusting to changes of these parameters.

scholarly journals The EISMINT benchmarks for testing ice-sheet models

1996 ◽  
Vol 23 ◽  
pp. 1-12 ◽  
Author(s):  
Philippe Huybrechts ◽  
Tony Payne ◽  
Keyword(s):  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Time Dependent ◽  
Ice Thickness ◽  
Operation Model ◽  
Time Dependent Behaviour ◽  
Model Benchmark ◽  
Dependent Behaviour ◽  
Ice Sheet Modelling

We present a series of benchmark experiments designed for testing and comparing numerical ice-sheet models. Following the outcome of two EISMINT workshops organized to intercompare large-scale ice-sheet models currently in operation, model benchmark experiments ate described for ice sheets under fixed and moving margin conditions. These address both steady-state and time-dependent behaviour under schematic boundary conditions and with prescribed physics. A comparison was made of each model’s prediction of basic geophysical variables such as ice thickness, velocity and temperature. Consensus achieved in the model inter-comparison provides reference solutions against which the accuracy and consistency of ice-sheet modelling codes can be assessed.

Indirect Estimation of the Djankuat Glacier Volume Based on Surface Topography

2002 ◽  
Vol 33 (1) ◽  
pp. 95-110 ◽  
Author(s):  
A. A. Aleynikov ◽  
V. V. Popovnin ◽  
K. F. Voytkovskiy ◽  
Ye. A. Zolotaryov
Keyword(s):  
Large Scale ◽  
Ice Thickness ◽  
Topographic Map ◽  
Glacier Surface ◽  
Ice Flow ◽  
Thermal Drilling ◽  
Calculation Results ◽  
Central Caucasus ◽  
The Relationship

The relationship between the thickness of a glacier stream and its surface slope is discussed. Morphometrical features of the glacier surface serve as a basis for estimating the maximum thickness the glacier can attain. A method for indirect calculation of ice thickness is hereby suggested. A detailed large-scale map permits determination of the total glacier volume. The Djankuat Glacier, a representative valley glacier in the Central Caucasus, is used as an example to illustrate the applicability of the proposed calculation scheme. Its probable thickness and volume are estimated on the grounds of photogrammetrical surveys, a topographic map and spatial pattern of ice flow velocity on the surface. Several values of directly measured ice thickness (by various methods such as thermal drilling, radar sounding, gravimetry etc.) verify the calculation results. As a result, ice thickness over the entire glacier area has been mapped. Methodical limitations and accuracy of indirect estimates are also discussed.

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.

scholarly journals The EISMINT benchmarks for testing ice-sheet models

1996 ◽  
Vol 23 ◽  
pp. 1-12 ◽  
Author(s):  
Philippe Huybrechts ◽  
Tony Payne ◽  
Keyword(s):  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Time Dependent ◽  
Ice Thickness ◽  
Operation Model ◽  
Time Dependent Behaviour ◽  
Model Benchmark ◽  
Dependent Behaviour ◽  
Ice Sheet Modelling

We present a series of benchmark experiments designed for testing and comparing numerical ice-sheet models. Following the outcome of two EISMINT workshops organized to intercompare large-scale ice-sheet models currently in operation, model benchmark experiments ate described for ice sheets under fixed and moving margin conditions. These address both steady-state and time-dependent behaviour under schematic boundary conditions and with prescribed physics. A comparison was made of each model’s prediction of basic geophysical variables such as ice thickness, velocity and temperature. Consensus achieved in the model inter-comparison provides reference solutions against which the accuracy and consistency of ice-sheet modelling codes can be assessed.

Large-Scale Numerical Modelling of the Antarctic Ice Sheet

1982 ◽  
Vol 3 ◽  
pp. 42-49 ◽  
Author(s):  
W.F. Budd ◽  
I.N. Smith
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Accumulation Rate ◽  
Ice Sheet ◽  
Ice Thickness ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Flow Parameters ◽  
The Antarctic ◽  
Thinning Rate

A large-scale dynamic numerical model of the Antarctic ice sheet has been developed to study its present state of ice flow and mass balance as well as its response to long-term changes of climate or sea-level.The flow of ice over a two-dimensional grid is determined from the ice thickness, the basal shear stress, the bedrock depth, and ice flow parameters derived from velocities of existing ice sheets. The change in ice thickness with time is governed by the continuity equation involving the ice flux divergence and the ice accumulation or ablation. At the ice sheet seaward boundary, a floating criterion and floating ice thinning rate apply. Bedrock depression with a time-delayed response dependent on the history of the ice load is also included.A 61 × 61 point grid with 100 km spacing has been used to represent the ice-sheet surface, bedrock, and accumulation rate. The model has been used to simul a te the growth of the present ice sheet and i ts reaction to changes of sea-level, bedrock depression, accumulation rate, ice flow parameters, and the iceshelf thinning rate.Preliminary results suggest that the present ice sheet is not in equilibrium but rather is still adjusting to changes of these parameters.

scholarly journals Large-scale force budget of an outlet glacier: Jutulstraumen, Dronning Maud Land, East Antarctica

2000 ◽  
Vol 30 ◽  
pp. 35-41 ◽  
Author(s):  
C. Rolstad ◽  
I. M. Whillans ◽  
J. O. Hagen ◽  
E. Isaksson
Keyword(s):  
Ground Penetrating Radar ◽  
Large Scale ◽  
Force Balance ◽  
Ice Thickness ◽  
Strain Rates ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Grounding Line ◽  
Dronning Maud Land ◽  
Ground Penetrating

AbstractA large-scale force budget was applied using a combination of remote-sensing and field data from Jutulstraumen, Dronning Maud Land, Antarctica. In the grounded area, more than 95 % of ice flow is balanced by basal friction. In a partly floating section near the grounding-line area, on average lateral drag provides 38% of resistance to flow.Measurement uncertainties were propagated through the calculation of forces. The accuracies of strain rates derived from satellite data (Landsat thematic mapper) were found adequate to calculate meaningful force-balance terms. For the floating section, where lateral forces contribute to controlling flow, the main contribution to errors in the force budget is uncertainty in the rate factor for the flow law of ice. For grounded sections, the uncertainty in ice thickness, as measured by ground-penetrating radar, contributes more or less equally to errors in the force budget as does that in the rate factor.

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>

Sign in / Sign up

Export Citation Format

Share Document