Shear margins in glaciers and ice sheets
Abstract Analytical and numerical techniques are used to examine the flow response of a sloped slab of power-law fluid (power n ) subjected to basal boundary conditions that vary spatially across the flow direction, as for example near an ice-stream margin with planar basal topography. The primary a...
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Online Access: | http://dx.doi.org/10.1017/s0022143000030550 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000030550 |
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crcambridgeupr:10.1017/s0022143000030550 2024-04-28T08:26:45+00:00 Shear margins in glaciers and ice sheets Raymond, Charles 1996 http://dx.doi.org/10.1017/s0022143000030550 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000030550 en eng Cambridge University Press (CUP) Journal of Glaciology volume 42, issue 140, page 90-102 ISSN 0022-1430 1727-5652 Earth-Surface Processes journal-article 1996 crcambridgeupr https://doi.org/10.1017/s0022143000030550 2024-04-09T06:55:44Z Abstract Analytical and numerical techniques are used to examine the flow response of a sloped slab of power-law fluid (power n ) subjected to basal boundary conditions that vary spatially across the flow direction, as for example near an ice-stream margin with planar basal topography. The primary assumption is that basal shear stress is proportional to the basal speed times a spatially variable slip resistance. The ratio of mean basal speed to the speed originating from shearing through the thickness. denoted as r , gives a measure of how slippery the bed is. The principal conclusion is that a localized disturbance in slip resistance affects the basal stress and speed in a zone spread over a greater width of the flow. In units of ice thickness H , the spatial scale of spreading is proportional to a single dimensionless number R n ≡ ( r / n + 1) 1/ n +1 derived from n and r . The consequence for a shear zone above a sharp jump in slip resistance is that the shearing is spread out over a boundary layer with a width proportional to R n . For an ice stream caused by a band of low slip resistance with a half-width of w H , the margins influence velocity and stress in the central part of the band depending on R n in comparison to w . Three regimes can be identified, which for n = 3 are quantified as follows: low r defined as R 3 < 0.1 w , for which the central flow is essentially unaffected by the margins and the driving stress is supported entire by by basal drag; high r defined as R 3 > 1 w , for which the boundary layers from both sides bridge across the full flow width and the driving stress in the center is supported almost entirely by side drag; intermediate r , for which the driving stress in the center is supported by a combination of basal and side drag. Shear zones that are narrower than predicted on the basis of this theory (≈ R 3 ) would require localized softening of the ice to explain the concentration of deformation at a shorter scale. Article in Journal/Newspaper Journal of Glaciology Cambridge University Press Journal of Glaciology 42 140 90 102 |
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Open Polar |
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Cambridge University Press |
op_collection_id |
crcambridgeupr |
language |
English |
topic |
Earth-Surface Processes |
spellingShingle |
Earth-Surface Processes Raymond, Charles Shear margins in glaciers and ice sheets |
topic_facet |
Earth-Surface Processes |
description |
Abstract Analytical and numerical techniques are used to examine the flow response of a sloped slab of power-law fluid (power n ) subjected to basal boundary conditions that vary spatially across the flow direction, as for example near an ice-stream margin with planar basal topography. The primary assumption is that basal shear stress is proportional to the basal speed times a spatially variable slip resistance. The ratio of mean basal speed to the speed originating from shearing through the thickness. denoted as r , gives a measure of how slippery the bed is. The principal conclusion is that a localized disturbance in slip resistance affects the basal stress and speed in a zone spread over a greater width of the flow. In units of ice thickness H , the spatial scale of spreading is proportional to a single dimensionless number R n ≡ ( r / n + 1) 1/ n +1 derived from n and r . The consequence for a shear zone above a sharp jump in slip resistance is that the shearing is spread out over a boundary layer with a width proportional to R n . For an ice stream caused by a band of low slip resistance with a half-width of w H , the margins influence velocity and stress in the central part of the band depending on R n in comparison to w . Three regimes can be identified, which for n = 3 are quantified as follows: low r defined as R 3 < 0.1 w , for which the central flow is essentially unaffected by the margins and the driving stress is supported entire by by basal drag; high r defined as R 3 > 1 w , for which the boundary layers from both sides bridge across the full flow width and the driving stress in the center is supported almost entirely by side drag; intermediate r , for which the driving stress in the center is supported by a combination of basal and side drag. Shear zones that are narrower than predicted on the basis of this theory (≈ R 3 ) would require localized softening of the ice to explain the concentration of deformation at a shorter scale. |
format |
Article in Journal/Newspaper |
author |
Raymond, Charles |
author_facet |
Raymond, Charles |
author_sort |
Raymond, Charles |
title |
Shear margins in glaciers and ice sheets |
title_short |
Shear margins in glaciers and ice sheets |
title_full |
Shear margins in glaciers and ice sheets |
title_fullStr |
Shear margins in glaciers and ice sheets |
title_full_unstemmed |
Shear margins in glaciers and ice sheets |
title_sort |
shear margins in glaciers and ice sheets |
publisher |
Cambridge University Press (CUP) |
publishDate |
1996 |
url |
http://dx.doi.org/10.1017/s0022143000030550 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000030550 |
genre |
Journal of Glaciology |
genre_facet |
Journal of Glaciology |
op_source |
Journal of Glaciology volume 42, issue 140, page 90-102 ISSN 0022-1430 1727-5652 |
op_doi |
https://doi.org/10.1017/s0022143000030550 |
container_title |
Journal of Glaciology |
container_volume |
42 |
container_issue |
140 |
container_start_page |
90 |
op_container_end_page |
102 |
_version_ |
1797586006142091264 |