scholarly journals Glacier geometry and flow speed determine how Arctic marine-terminating glaciers respond to lubricated beds

2021 ◽  
Author(s):  
Whyjay Zheng
Keyword(s):  
Initial Perturbation ◽  
Flow Characteristics ◽  
Flow Speed ◽  
Ice Thickness ◽  
Initial Speed ◽  
Surface Slope ◽  
Ice Flow ◽  
Ice Cap ◽  
Speed Change ◽  
Dynamic Discharge

Abstract. Basal conditions directly control the glacier sliding rate and the dynamic discharge of ice flow. Recent glacier destabilization events indicate that some marine-terminating glaciers quickly respond to lubricated beds with increased flow speed, but the underlying physics, especially how this vulnerability relates to glacier geometry and flow characteristics, remains unclear. This paper presents a 1-D physical framework for glacier dynamic vulnerability assuming sudden basal lubrication as an initial perturbation. In this new model, two quantities determine the scale and the areal extent of the subsequent thinning and acceleration after the bed is lubricated: Péclet number (Pe) and the product of glacier speed and thickness gradient (dubbed J0 in this study). To validate the model, this paper calculates Pe and J0 using multi-sourced data from 1996–1998 for outlet glaciers in Greenland and Austfonna Ice Cap, Svalbard, and compares the results with the glacier speed change during 1996/1998–2018. Glaciers with lower Pe and J0 are more likely to accelerate during this 20-year span than those with higher Pe and J0, which matches the model prediction. A combined factor of ice thickness, surface slope, and initial speed for ice flow physically determines how much and how fast glaciers respond to lubricated beds, as forms of speed, elevation, and terminus change.

On the relation between ice thickness changes and glacier speed-up, with application to Pine Island Glacier in West Antarctica 

2021 ◽  
Author(s):  
Jan De Rydt ◽  
Ronja Reese ◽  
Fernando Paolo ◽  
G Hilmar Gudmundsson
Keyword(s):  
Numerical Solutions ◽  
Numerical Models ◽  
Flow Speed ◽  
Ice Thickness ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Flow ◽  
Spatially Distributed ◽  
Speed Up ◽  
Induced Changes

<p>Pine Island Glacier in West Antarctica is among the fastest changing glaciers worldwide. Much of its fast-flowing central trunk is thinning and accelerating, a process thought to have been triggered by ocean-induced changes in ice-shelf buttressing. The measured acceleration in response to perturbations in ice thickness is a non-trivial manifestation of several poorly-understood physical processes, including the transmission of stresses between the ice and underlying bed. To enable robust projections of future ice flow, it is imperative that numerical models include an accurate representation of these processes. Here we combine the latest data with analytical and numerical solutions of SSA ice flow to show that the recent increase in flow speed of Pine Island Glacier is only compatible with observed patterns of thinning if a spatially distributed, predominantly plastic bed underlies large parts of the central glacier and its upstream tributaries.</p>

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 Variability in ice motion and dynamic discharge from Devon Ice Cap, Nunavut, Canada

2017 ◽  
Vol 63 (239) ◽  
pp. 436-449 ◽  
Author(s):  
WESLEY VAN WYCHEN ◽  
JAMIE DAVIS ◽  
LUKE COPLAND ◽  
DAVID O. BURGESS ◽  
LAURENCE GRAY ◽  
...  
Keyword(s):  
Feature Tracking ◽  
Ice Thickness ◽  
Tidewater Glaciers ◽  
Bed Topography ◽  
Ice Cap ◽  
The North ◽  
Landsat 7 ◽  
Devon Ice Cap ◽  
Dynamic Discharge ◽  
Observation Period

ABSTRACTFeature tracking of approximately annually separated Landsat-7 ETM+ imagery acquired from 1999 to 2010 and speckle tracking of 24-day separated RADARSAT-2 imagery acquired from 2009 to 2015 reveal that motion of the major tidewater glaciers of Devon Ice Cap is more variable than previously described. The flow of almost half (six of 14) of the outlet glaciers slowed over the observation period, while that of the terminus regions of three of 14 of the glaciers sped up in the most recent years of observation. The North Croker Bay Glacier of southern Devon Ice Cap showed the greatest variability in motion, oscillating between multi-year (three or more) periods of slower and faster flow and exhibited a pattern of velocity variability that is different from that of the rest of the ice cap's outlet glaciers. Comparisons between areas of dynamic variability and glacier bed topography indicate that velocity variability is largely restricted to regions where the glacier bed is grounded below sea level. Derived velocities are combined with measurements of ice thickness at the fronts of tidewater glacier to determine a mean annual (2009; 2011–15) dynamic ice discharge of 0.41 ± 0.11 Gt a−1for Devon Ice Cap. The Belcher Glacier is becoming a larger source of mass loss via ice discharge.

Ice Flow and Mass Changes of Lewis Glacier, Mount Kenya, East Africa: Observations 1974–86, Modelling, and Predictions to the Year 2000 AD

1989 ◽  
Vol 35 (121) ◽  
pp. 325-332 ◽  
Author(s):  
Stefan Hastenrath
Keyword(s):  
Model Performance ◽  
Climatic Conditions ◽  
Ice Thickness ◽  
Volume Flux ◽  
Surface Slope ◽  
Time Step ◽  
Climatic Forcing ◽  
Ice Flow ◽  
Future Evolution ◽  
Year 2000

AbstractThe study is based on an observation program since 1974, including the continuous monitoring of net balance during 1978–86. The 8 year vertical net-balance profile, characterized by negative values throughout and an increase of absolute amounts from the higher towards the lower elevations, defines the recent climatic forcing.A model is developed with a spatial resolution by 100 m wide bands, relating glacier morphology, ice flow, and mass economy, using as input ice thickness, surface slope, width of height contours, area of 100 m wide bands, volume flux, and net balance as a function of elevation. In 1 year time steps, the model calculates the changes in ice thickness and surface topography commensurate with the difference between net balance and longitudinal divergence of volume flux, and then the corresponding changes in surface slope, contour width, area of 100 m wide bands, volume flux, and net balance corresponding to the new surface elevations. This information serves as input for the next time step.The model was applied to the intervals 1974–78, 1978–82, and 1982–86, as training periods, to explore the diagnostics of ice flow and mass economy, and to ascertain the model performance in treating long-term evolution in glacier behavior. The experiments yielded a reasonable agreement between calculated and observed changes in ice thickness, velocity, and volume flux, over the three aforementioned 4 year periods of field monitoring. Two sets of prediction experiments beyond 1986 were then undertaken. The first used as input the observed 1978–86 vertical net-balance profile (a), and thus simulated the future evolution of the glacier given continuation of the recent climatic forcing. In the second set of experiments, the 1978–86 net-balance values were doubled to yield a more extreme net-balance profile (b), representing climatic conditions considerably more adverse to the maintenance of the glacier.Predictions are presented for the epochs 1990, 1994, 1998, and 2000. Given continuation of the recent climatic conditions (profile a), the following changes are anticipated from 1986 to the year 2000: a shrinkage of the volume from 4 to 1 x 106m3; an area decrease from 25 to 17 χ 104m2; a shortening of the glacier from 990 to less than 800 m; a slow-down of fastest ice flow from 2.5 to less than 1ma−1; a decrease of the maximum volume flux from 13 to less than 3 χ 103m3a−1; and substantial up-glacier displacements of the velocity and volume-flux maxima. Under more extreme negative net-balance conditions (profile b), the decay would be so greatly accelerated that Lewis Glacier may completely disappear well before the end of the millennium. This prospect is inherent in a possible change from recent climatic conditions.

scholarly journals Assessment of ice flow dynamics in the zone close to the calving front of Antarctic ice shelves

2015 ◽  
Vol 61 (230) ◽  
pp. 1194-1206 ◽  
Author(s):  
Martin G. Wearing ◽  
Richard C.A. Hindmarsh ◽  
M. Grae Worster
Keyword(s):  
Flow Speed ◽  
Flow Dynamics ◽  
Rheological Parameters ◽  
Ice Thickness ◽  
Scaling Analysis ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
The Relationship ◽  
Good Agreement

AbstractWe investigate the relationship between four ice-shelf characteristics in the area close to the calving front: ice flow speed, strain rate, ice thickness and shelf width. Data are compiled for these glaciological parameters at the calving fronts of 22 Antarctic ice shelves. Clarification concerning the viscous supply of ice to the calving front is sought following the empirical calving law of Alley and others (2008), derived from a similar but smaller dataset, and the scaling analysis of Hindmarsh (2012). The dataset is analysed and good agreement is observed between the expected theoretical scaling and geophysical data for the flow of ice near the calving front in the case of ice shelves that are laterally confined and have uniform rheology. The lateral confinement ensures flow is aligned in the along-shelf direction, and uniform rheological parameters mean resistance to flow is provided by near-stationary ice in the grounded margins. In other cases, the velocity is greater than predicted, which we attribute to marginal weakening or the presence of ice tongues.

Ice Flow Over Bedrock Perturbations

1970 ◽  
Vol 9 (55) ◽  
pp. 29-48 ◽  
Author(s):  
W.F. Budd
Keyword(s):  
Surface Shape ◽  
Ice Thickness ◽  
Damping Factor ◽  
Strain Rates ◽  
Longitudinal Stress ◽  
Surface Slope ◽  
Stress Equation ◽  
Ice Flow ◽  
Small Surface ◽  
Ice Caps

AbstractThe use of well known simple periodic solutions of the two-dimensional biharmonic stress equation for studying the flow over undulations of an ice mass of small surface slope is examined. The model considered is one in which most of the shear (deformation or. sliding) takes place near the base and the upper part moves largely as a block, with longitudinal strain-rates varying linearly with the longitudinal stress deviations. For bedrock perturbations of a given wavelength the steady-state surface shape consists of similar waves but out of phase by ½π, such that the steepest slope occurs over the highest bedrock; and the amplitude is reduced by a “damping factor”, depending on the speed, viscosity, ice thickness and wavelength.Minimum damping occurs for λm ≈ 3.3 times the ice thickness, while waves much longer or much shorter than this are almost completely damped out. The energy dissipation and the resistance to the ice flow is also a maximum for an undulation scale of several times the ice thickness, whereas the effects of small basal irregularities die out exponentially with distance into the ice, and only have an effect in so far as the average basal stress is related to the average surface slope. As a result of this a revision of present glacier sliding theories becomes possible.Various predictions of the theory have been confirmed from spectral analysis of surface and bedrock profiles of ice caps.

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 and Mass Changes of Lewis Glacier, Mount Kenya, East Africa: Observations 1974–86, Modelling, and Predictions to the Year 2000 AD

1989 ◽  
Vol 35 (121) ◽  
pp. 325-332 ◽  
Author(s):  
Stefan Hastenrath
Keyword(s):  
Model Performance ◽  
Climatic Conditions ◽  
Ice Thickness ◽  
Volume Flux ◽  
Surface Slope ◽  
Time Step ◽  
Climatic Forcing ◽  
Ice Flow ◽  
Future Evolution ◽  
Year 2000

AbstractThe study is based on an observation program since 1974, including the continuous monitoring of net balance during 1978–86. The 8 year vertical net-balance profile, characterized by negative values throughout and an increase of absolute amounts from the higher towards the lower elevations, defines the recent climatic forcing.A model is developed with a spatial resolution by 100 m wide bands, relating glacier morphology, ice flow, and mass economy, using as input ice thickness, surface slope, width of height contours, area of 100 m wide bands, volume flux, and net balance as a function of elevation. In 1 year time steps, the model calculates the changes in ice thickness and surface topography commensurate with the difference between net balance and longitudinal divergence of volume flux, and then the corresponding changes in surface slope, contour width, area of 100 m wide bands, volume flux, and net balance corresponding to the new surface elevations. This information serves as input for the next time step.The model was applied to the intervals 1974–78, 1978–82, and 1982–86, as training periods, to explore the diagnostics of ice flow and mass economy, and to ascertain the model performance in treating long-term evolution in glacier behavior. The experiments yielded a reasonable agreement between calculated and observed changes in ice thickness, velocity, and volume flux, over the three aforementioned 4 year periods of field monitoring. Two sets of prediction experiments beyond 1986 were then undertaken. The first used as input the observed 1978–86 vertical net-balance profile (a), and thus simulated the future evolution of the glacier given continuation of the recent climatic forcing. In the second set of experiments, the 1978–86 net-balance values were doubled to yield a more extreme net-balance profile (b), representing climatic conditions considerably more adverse to the maintenance of the glacier.Predictions are presented for the epochs 1990, 1994, 1998, and 2000. Given continuation of the recent climatic conditions (profile a), the following changes are anticipated from 1986 to the year 2000: a shrinkage of the volume from 4 to 1 x 106 m3; an area decrease from 25 to 17 χ 104 m2; a shortening of the glacier from 990 to less than 800 m; a slow-down of fastest ice flow from 2.5 to less than 1ma−1; a decrease of the maximum volume flux from 13 to less than 3 χ 103 m3 a−1; and substantial up-glacier displacements of the velocity and volume-flux maxima. Under more extreme negative net-balance conditions (profile b), the decay would be so greatly accelerated that Lewis Glacier may completely disappear well before the end of the millennium. This prospect is inherent in a possible change from recent climatic conditions.

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 Over Bedrock Perturbations

1970 ◽  
Vol 9 (55) ◽  
pp. 29-48 ◽  
Author(s):  
W.F. Budd
Keyword(s):  
Surface Shape ◽  
Ice Thickness ◽  
Damping Factor ◽  
Strain Rates ◽  
Longitudinal Stress ◽  
Surface Slope ◽  
Stress Equation ◽  
Ice Flow ◽  
Small Surface ◽  
Ice Caps

AbstractThe use of well known simple periodic solutions of the two-dimensional biharmonic stress equation for studying the flow over undulations of an ice mass of small surface slope is examined. The model considered is one in which most of the shear (deformation or. sliding) takes place near the base and the upper part moves largely as a block, with longitudinal strain-rates varying linearly with the longitudinal stress deviations. For bedrock perturbations of a given wavelength the steady-state surface shape consists of similar waves but out of phase by ½π, such that the steepest slope occurs over the highest bedrock; and the amplitude is reduced by a “damping factor”, depending on the speed, viscosity, ice thickness and wavelength.Minimum damping occurs forλm≈ 3.3 times the ice thickness, while waves much longer or much shorter than this are almost completely damped out. The energy dissipation and the resistance to the ice flow is also a maximum for an undulation scale of several times the ice thickness, whereas the effects of small basal irregularities die out exponentially with distance into the ice, and only have an effect in so far as the average basal stress is related to the average surface slope. As a result of this a revision of present glacier sliding theories becomes possible.Various predictions of the theory have been confirmed from spectral analysis of surface and bedrock profiles of ice caps.

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