Coupling between a glacier and a soft bed: II Model results
Abstract The relation between the local effective pressure and shear stress on till beneath Storglaciären, Sweden, discussed in Iverson and others (1999), provides an empirical basis for studying the processes that control the strength of the ice/bed coupling. Particles in the bed that protrude into...
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Online Access: | http://dx.doi.org/10.1017/s0022143000003026 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000003026 |
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crcambridgeupr:10.1017/s0022143000003026 2024-09-15T17:42:46+00:00 Coupling between a glacier and a soft bed: II Model results Iverson, Neal R. 1999 http://dx.doi.org/10.1017/s0022143000003026 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000003026 en eng Cambridge University Press (CUP) https://www.cambridge.org/core/terms Journal of Glaciology volume 45, issue 149, page 41-53 ISSN 0022-1430 1727-5652 journal-article 1999 crcambridgeupr https://doi.org/10.1017/s0022143000003026 2024-08-28T04:02:57Z Abstract The relation between the local effective pressure and shear stress on till beneath Storglaciären, Sweden, discussed in Iverson and others (1999), provides an empirical basis for studying the processes that control the strength of the ice/bed coupling. Particles in the bed that protrude into the glacier sole support shear stresses that are limited by either ploughing or the traditional sliding mechanisms. Model calculations, based on studies of cone penetration through fine-grained sediment and sliding theory, agree with the observed relation between shear stress and effective pressure if the water layer at the ice/bed interface is assumed to thicken rapidly as the effective pressure approaches zero. Studies of the hydraulics of linked cavities provide support for this assumption, if the mean thickness of the water layer reflects the extent of microcavity development at the interface. Comparison of the calculated shear stress with the ultimate strength of till suggests that bed deformation limits the shear stress on till beneath Storglaciären only at intermediate effective pressures; at very low effective pressures, like those inferred at the site of the tiltmeter discussed in Iverson and others (1999), and at sufficiently high effective pressures, ploughing and sliding should focus motion near the glacier sole. A calculation using parameter values appropriate for Ice Stream B, West Antarctica, suggests that ploughing may occur there at shear stresses not sufficient to deform the bed at depth. This conclusion is reinforced by the likelihood that pore pressures in excess of hydrostatic should develop down-glacier from ploughing particles, thereby weakening the bed near the glacier sole. However, given the apparent sensitivity of the ice/bed coupling to basal conditions that may be highly variable, any blanket assumption regarding the flow mechanism of ice masses on soft beds should probably be viewed with skepticism. Article in Journal/Newspaper Antarc* Antarctica Ice Stream B Journal of Glaciology West Antarctica Cambridge University Press Journal of Glaciology 45 149 41 53 |
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Open Polar |
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Cambridge University Press |
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English |
description |
Abstract The relation between the local effective pressure and shear stress on till beneath Storglaciären, Sweden, discussed in Iverson and others (1999), provides an empirical basis for studying the processes that control the strength of the ice/bed coupling. Particles in the bed that protrude into the glacier sole support shear stresses that are limited by either ploughing or the traditional sliding mechanisms. Model calculations, based on studies of cone penetration through fine-grained sediment and sliding theory, agree with the observed relation between shear stress and effective pressure if the water layer at the ice/bed interface is assumed to thicken rapidly as the effective pressure approaches zero. Studies of the hydraulics of linked cavities provide support for this assumption, if the mean thickness of the water layer reflects the extent of microcavity development at the interface. Comparison of the calculated shear stress with the ultimate strength of till suggests that bed deformation limits the shear stress on till beneath Storglaciären only at intermediate effective pressures; at very low effective pressures, like those inferred at the site of the tiltmeter discussed in Iverson and others (1999), and at sufficiently high effective pressures, ploughing and sliding should focus motion near the glacier sole. A calculation using parameter values appropriate for Ice Stream B, West Antarctica, suggests that ploughing may occur there at shear stresses not sufficient to deform the bed at depth. This conclusion is reinforced by the likelihood that pore pressures in excess of hydrostatic should develop down-glacier from ploughing particles, thereby weakening the bed near the glacier sole. However, given the apparent sensitivity of the ice/bed coupling to basal conditions that may be highly variable, any blanket assumption regarding the flow mechanism of ice masses on soft beds should probably be viewed with skepticism. |
format |
Article in Journal/Newspaper |
author |
Iverson, Neal R. |
spellingShingle |
Iverson, Neal R. Coupling between a glacier and a soft bed: II Model results |
author_facet |
Iverson, Neal R. |
author_sort |
Iverson, Neal R. |
title |
Coupling between a glacier and a soft bed: II Model results |
title_short |
Coupling between a glacier and a soft bed: II Model results |
title_full |
Coupling between a glacier and a soft bed: II Model results |
title_fullStr |
Coupling between a glacier and a soft bed: II Model results |
title_full_unstemmed |
Coupling between a glacier and a soft bed: II Model results |
title_sort |
coupling between a glacier and a soft bed: ii model results |
publisher |
Cambridge University Press (CUP) |
publishDate |
1999 |
url |
http://dx.doi.org/10.1017/s0022143000003026 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000003026 |
genre |
Antarc* Antarctica Ice Stream B Journal of Glaciology West Antarctica |
genre_facet |
Antarc* Antarctica Ice Stream B Journal of Glaciology West Antarctica |
op_source |
Journal of Glaciology volume 45, issue 149, page 41-53 ISSN 0022-1430 1727-5652 |
op_rights |
https://www.cambridge.org/core/terms |
op_doi |
https://doi.org/10.1017/s0022143000003026 |
container_title |
Journal of Glaciology |
container_volume |
45 |
container_issue |
149 |
container_start_page |
41 |
op_container_end_page |
53 |
_version_ |
1810489501919739904 |