The Formation of Fjord Thresholds
Abstract The erosion rate of bedrock by glacier action is analyzed under conditions of constant-state radial convergent and divergent flow, assuming that the quarrying rate increases with increasing sliding velocity, and assuming a conventional power-function sliding law. Ice is modeled as a non-lin...
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Cambridge University Press (CUP)
1986
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Online Access: | http://dx.doi.org/10.1017/s0022143000006894 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000006894 |
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crcambridgeupr:10.1017/s0022143000006894 2024-03-03T08:46:09+00:00 The Formation of Fjord Thresholds Shoemaker, E. M. 1986 http://dx.doi.org/10.1017/s0022143000006894 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000006894 en eng Cambridge University Press (CUP) Journal of Glaciology volume 32, issue 110, page 65-71 ISSN 0022-1430 1727-5652 Earth-Surface Processes journal-article 1986 crcambridgeupr https://doi.org/10.1017/s0022143000006894 2024-02-08T08:41:37Z Abstract The erosion rate of bedrock by glacier action is analyzed under conditions of constant-state radial convergent and divergent flow, assuming that the quarrying rate increases with increasing sliding velocity, and assuming a conventional power-function sliding law. Ice is modeled as a non-linear Glen material. Deviatoric stresses are computed but are shown to be negligible compared to the basal shear stress, provided that suitable restraints are placed on the ratio of channel radius of curvature to ice thickness. If the ice is sufficiently thick, radial divergent flow results in erosion rates which decrease in the down-stream direction This provides an explanation for the formation of the largest class of fjord thresholds which occur at channel widenings. In contrast, increased erosion rates are predicted at narrows which can explain the presence of deep troughs at gradual narrows. It is argued that the presence of pronounced thresholds in abrupt narrows can be explained by low quarryability or locally high roughness which reduces the sliding velocity. The origin of till overlying thresholds is explained as a natural consequence of a threshold being a position of relative stability for the terminus of a retreating tide-water glacier. Article in Journal/Newspaper Journal of Glaciology Cambridge University Press Journal of Glaciology 32 110 65 71 |
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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 Shoemaker, E. M. The Formation of Fjord Thresholds |
topic_facet |
Earth-Surface Processes |
description |
Abstract The erosion rate of bedrock by glacier action is analyzed under conditions of constant-state radial convergent and divergent flow, assuming that the quarrying rate increases with increasing sliding velocity, and assuming a conventional power-function sliding law. Ice is modeled as a non-linear Glen material. Deviatoric stresses are computed but are shown to be negligible compared to the basal shear stress, provided that suitable restraints are placed on the ratio of channel radius of curvature to ice thickness. If the ice is sufficiently thick, radial divergent flow results in erosion rates which decrease in the down-stream direction This provides an explanation for the formation of the largest class of fjord thresholds which occur at channel widenings. In contrast, increased erosion rates are predicted at narrows which can explain the presence of deep troughs at gradual narrows. It is argued that the presence of pronounced thresholds in abrupt narrows can be explained by low quarryability or locally high roughness which reduces the sliding velocity. The origin of till overlying thresholds is explained as a natural consequence of a threshold being a position of relative stability for the terminus of a retreating tide-water glacier. |
format |
Article in Journal/Newspaper |
author |
Shoemaker, E. M. |
author_facet |
Shoemaker, E. M. |
author_sort |
Shoemaker, E. M. |
title |
The Formation of Fjord Thresholds |
title_short |
The Formation of Fjord Thresholds |
title_full |
The Formation of Fjord Thresholds |
title_fullStr |
The Formation of Fjord Thresholds |
title_full_unstemmed |
The Formation of Fjord Thresholds |
title_sort |
formation of fjord thresholds |
publisher |
Cambridge University Press (CUP) |
publishDate |
1986 |
url |
http://dx.doi.org/10.1017/s0022143000006894 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000006894 |
genre |
Journal of Glaciology |
genre_facet |
Journal of Glaciology |
op_source |
Journal of Glaciology volume 32, issue 110, page 65-71 ISSN 0022-1430 1727-5652 |
op_doi |
https://doi.org/10.1017/s0022143000006894 |
container_title |
Journal of Glaciology |
container_volume |
32 |
container_issue |
110 |
container_start_page |
65 |
op_container_end_page |
71 |
_version_ |
1792502119921614848 |