The marginal shear stress of Ice Stream B, West Antarctica
To ascertain whether the velocity of Ice Stream B, West Antarctica, may be controlled by the stress in its marginal shear zones (the "Snake" and the "Dragon"), we undertook a determination of the marginal shear stress in the Dragon near Camp Up B by using ice itself as a stress m...
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ftcaltechauth:oai:authors.library.caltech.edu:47277 2023-05-15T13:55:33+02:00 The marginal shear stress of Ice Stream B, West Antarctica Jackson, Miriam Kamb, Barclay 1997 application/pdf https://authors.library.caltech.edu/47277/ https://authors.library.caltech.edu/47277/1/Kamb_1997p415.pdf https://resolver.caltech.edu/CaltechAUTHORS:20140716-162056262 unknown International Glaciological Society https://authors.library.caltech.edu/47277/1/Kamb_1997p415.pdf Jackson, Miriam and Kamb, Barclay (1997) The marginal shear stress of Ice Stream B, West Antarctica. Journal of Glaciology, 43 (145). pp. 415-426. ISSN 0022-1430. https://resolver.caltech.edu/CaltechAUTHORS:20140716-162056262 <https://resolver.caltech.edu/CaltechAUTHORS:20140716-162056262> Article PeerReviewed 1997 ftcaltechauth 2020-04-26T16:44:34Z To ascertain whether the velocity of Ice Stream B, West Antarctica, may be controlled by the stress in its marginal shear zones (the "Snake" and the "Dragon"), we undertook a determination of the marginal shear stress in the Dragon near Camp Up B by using ice itself as a stress meter. The observed marginal shear strain rate of 0.14 a^(-1) is used to calculate the marginal shear stress from the flow law of ice determined by creep tests on ice cores from a depth of 300 m in the Dragon, obtained by using a hot-water ice-coring drill. The test-specimen orientation relative to the stress axes in the tests is chosen on the basis of c-axis fabrics so that the test applies horizontal shear across vertical planes parallel to the margin. The resulting marginal shear stress is (2.2 ± 0.3) × 10^5 Pa. This implies that 63-100% of the ice stream's support against gravitational loading comes from the margins and only 37-0% from the base, so that the margins play an important role in controlling the ice-stream motion. The marginal shear-stress value is twice that given by the ice-stream model of Echelmeyer and others (1994} and the corresponding strain-rate enhancement factors differ greatly (E ≈ 1-2 vs 10-12.5). This large discrepancy could be explained by recrystallization of the ice during or shortly after coring. Estimates of the expected recrystallization time-scale bracket the ~1 h time-scale of coring and leave the likelihood of recrystallization uncertain. However, the observed two-maximum fabric type is not what is expected for annealing recrystallization from the sharp single-maximum fabric that would be expected in situ at the high shear strains involved (γ~20). Experimental data from Wilson (1982) suggest that, if the core did recrystallize, the prior fabric was a two-maximum fabric not substantially different from the observed one, which implies that the measured flow law and derived marginal shear stress are applicable to the in situ situation. These issues need to be resolved by further work to obtain a more definitive observational assessment of the marginal shear stress. Article in Journal/Newspaper Antarc* Antarctica Antarctica Journal Ice Stream B Journal of Glaciology West Antarctica Caltech Authors (California Institute of Technology) West Antarctica |
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To ascertain whether the velocity of Ice Stream B, West Antarctica, may be controlled by the stress in its marginal shear zones (the "Snake" and the "Dragon"), we undertook a determination of the marginal shear stress in the Dragon near Camp Up B by using ice itself as a stress meter. The observed marginal shear strain rate of 0.14 a^(-1) is used to calculate the marginal shear stress from the flow law of ice determined by creep tests on ice cores from a depth of 300 m in the Dragon, obtained by using a hot-water ice-coring drill. The test-specimen orientation relative to the stress axes in the tests is chosen on the basis of c-axis fabrics so that the test applies horizontal shear across vertical planes parallel to the margin. The resulting marginal shear stress is (2.2 ± 0.3) × 10^5 Pa. This implies that 63-100% of the ice stream's support against gravitational loading comes from the margins and only 37-0% from the base, so that the margins play an important role in controlling the ice-stream motion. The marginal shear-stress value is twice that given by the ice-stream model of Echelmeyer and others (1994} and the corresponding strain-rate enhancement factors differ greatly (E ≈ 1-2 vs 10-12.5). This large discrepancy could be explained by recrystallization of the ice during or shortly after coring. Estimates of the expected recrystallization time-scale bracket the ~1 h time-scale of coring and leave the likelihood of recrystallization uncertain. However, the observed two-maximum fabric type is not what is expected for annealing recrystallization from the sharp single-maximum fabric that would be expected in situ at the high shear strains involved (γ~20). Experimental data from Wilson (1982) suggest that, if the core did recrystallize, the prior fabric was a two-maximum fabric not substantially different from the observed one, which implies that the measured flow law and derived marginal shear stress are applicable to the in situ situation. These issues need to be resolved by further work to obtain a more definitive observational assessment of the marginal shear stress. |
format |
Article in Journal/Newspaper |
author |
Jackson, Miriam Kamb, Barclay |
spellingShingle |
Jackson, Miriam Kamb, Barclay The marginal shear stress of Ice Stream B, West Antarctica |
author_facet |
Jackson, Miriam Kamb, Barclay |
author_sort |
Jackson, Miriam |
title |
The marginal shear stress of Ice Stream B, West Antarctica |
title_short |
The marginal shear stress of Ice Stream B, West Antarctica |
title_full |
The marginal shear stress of Ice Stream B, West Antarctica |
title_fullStr |
The marginal shear stress of Ice Stream B, West Antarctica |
title_full_unstemmed |
The marginal shear stress of Ice Stream B, West Antarctica |
title_sort |
marginal shear stress of ice stream b, west antarctica |
publisher |
International Glaciological Society |
publishDate |
1997 |
url |
https://authors.library.caltech.edu/47277/ https://authors.library.caltech.edu/47277/1/Kamb_1997p415.pdf https://resolver.caltech.edu/CaltechAUTHORS:20140716-162056262 |
geographic |
West Antarctica |
geographic_facet |
West Antarctica |
genre |
Antarc* Antarctica Antarctica Journal Ice Stream B Journal of Glaciology West Antarctica |
genre_facet |
Antarc* Antarctica Antarctica Journal Ice Stream B Journal of Glaciology West Antarctica |
op_relation |
https://authors.library.caltech.edu/47277/1/Kamb_1997p415.pdf Jackson, Miriam and Kamb, Barclay (1997) The marginal shear stress of Ice Stream B, West Antarctica. Journal of Glaciology, 43 (145). pp. 415-426. ISSN 0022-1430. https://resolver.caltech.edu/CaltechAUTHORS:20140716-162056262 <https://resolver.caltech.edu/CaltechAUTHORS:20140716-162056262> |
_version_ |
1766262261134917632 |