In situ stress tensor measured in an Alaskan glacier
An experimental program at Worthington Glacier, Alaska, U.S.A., has yielded the first in situ measurements of the full stress tensor in glacier ice. Measurements were made with an array of stiff (low-compliance) normal-force sensors frozen into a borehole at 120 m depth. Freezing in temperate ice wa...
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ftunivmontana:oai:scholarworks.umt.edu:geosci_pubs-1039 2024-09-09T19:41:12+00:00 In situ stress tensor measured in an Alaskan glacier Pfeffer, W. Tad Humphrey, Neil Amadei, B. Harper, Joel T. Wegmann, J. 2000-01-01T08:00:00Z application/pdf https://scholarworks.umt.edu/geosci_pubs/35 https://doi.org/10.3189/172756400781820354 https://scholarworks.umt.edu/context/geosci_pubs/article/1039/viewcontent/In_situ_stress_tensor_measured_in_an_Alaskan_glacier.pdf unknown ScholarWorks at University of Montana https://scholarworks.umt.edu/geosci_pubs/35 doi:10.3189/172756400781820354 https://scholarworks.umt.edu/context/geosci_pubs/article/1039/viewcontent/In_situ_stress_tensor_measured_in_an_Alaskan_glacier.pdf © 2000 International Glaciological Society Geosciences Faculty Publications Earth Sciences Glaciology text 2000 ftunivmontana https://doi.org/10.3189/172756400781820354 2024-06-20T05:32:53Z An experimental program at Worthington Glacier, Alaska, U.S.A., has yielded the first in situ measurements of the full stress tensor in glacier ice. Measurements were made with an array of stiff (low-compliance) normal-force sensors frozen into a borehole at 120 m depth. Freezing in temperate ice was accomplished by a down-hole heat exchanger which extracted heat at the rate of 15 W. Under slowly varying stress conditions, relaxation of stress anomalies by viscous creep following drilling of the hole and installation of the sensors allows for equilibration of measured stresses with far-field stresses. Equilibration of local and far-field stresses was confirmed and pressure sensor calibrated in laboratory experiments prior to the field program. Results of the stress measurements show principal axes of the stress tensor oriented in directions consistent with the geometry of the glacier and broadly consistent with measured englacial strain rate. The magnitudes of stress-tensor components are more error-prone and more sensitive to uncertainty in sensor magnitude than uncertainty in sensor orientation. Mean stress determined by pressure measurements agrees with estimated lithostatic overburden with within approximately 15%. Unexpected results include a stress perturbation lasted about 5 days that caused a rotation of the orientations of the principal stress axes of approximately 5 degrees about an axis pointing in the down-flow direction. Text glacier Alaska University of Montana: ScholarWorks Annals of Glaciology 31 229 235 |
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University of Montana: ScholarWorks |
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ftunivmontana |
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topic |
Earth Sciences Glaciology |
spellingShingle |
Earth Sciences Glaciology Pfeffer, W. Tad Humphrey, Neil Amadei, B. Harper, Joel T. Wegmann, J. In situ stress tensor measured in an Alaskan glacier |
topic_facet |
Earth Sciences Glaciology |
description |
An experimental program at Worthington Glacier, Alaska, U.S.A., has yielded the first in situ measurements of the full stress tensor in glacier ice. Measurements were made with an array of stiff (low-compliance) normal-force sensors frozen into a borehole at 120 m depth. Freezing in temperate ice was accomplished by a down-hole heat exchanger which extracted heat at the rate of 15 W. Under slowly varying stress conditions, relaxation of stress anomalies by viscous creep following drilling of the hole and installation of the sensors allows for equilibration of measured stresses with far-field stresses. Equilibration of local and far-field stresses was confirmed and pressure sensor calibrated in laboratory experiments prior to the field program. Results of the stress measurements show principal axes of the stress tensor oriented in directions consistent with the geometry of the glacier and broadly consistent with measured englacial strain rate. The magnitudes of stress-tensor components are more error-prone and more sensitive to uncertainty in sensor magnitude than uncertainty in sensor orientation. Mean stress determined by pressure measurements agrees with estimated lithostatic overburden with within approximately 15%. Unexpected results include a stress perturbation lasted about 5 days that caused a rotation of the orientations of the principal stress axes of approximately 5 degrees about an axis pointing in the down-flow direction. |
format |
Text |
author |
Pfeffer, W. Tad Humphrey, Neil Amadei, B. Harper, Joel T. Wegmann, J. |
author_facet |
Pfeffer, W. Tad Humphrey, Neil Amadei, B. Harper, Joel T. Wegmann, J. |
author_sort |
Pfeffer, W. Tad |
title |
In situ stress tensor measured in an Alaskan glacier |
title_short |
In situ stress tensor measured in an Alaskan glacier |
title_full |
In situ stress tensor measured in an Alaskan glacier |
title_fullStr |
In situ stress tensor measured in an Alaskan glacier |
title_full_unstemmed |
In situ stress tensor measured in an Alaskan glacier |
title_sort |
in situ stress tensor measured in an alaskan glacier |
publisher |
ScholarWorks at University of Montana |
publishDate |
2000 |
url |
https://scholarworks.umt.edu/geosci_pubs/35 https://doi.org/10.3189/172756400781820354 https://scholarworks.umt.edu/context/geosci_pubs/article/1039/viewcontent/In_situ_stress_tensor_measured_in_an_Alaskan_glacier.pdf |
genre |
glacier Alaska |
genre_facet |
glacier Alaska |
op_source |
Geosciences Faculty Publications |
op_relation |
https://scholarworks.umt.edu/geosci_pubs/35 doi:10.3189/172756400781820354 https://scholarworks.umt.edu/context/geosci_pubs/article/1039/viewcontent/In_situ_stress_tensor_measured_in_an_Alaskan_glacier.pdf |
op_rights |
© 2000 International Glaciological Society |
op_doi |
https://doi.org/10.3189/172756400781820354 |
container_title |
Annals of Glaciology |
container_volume |
31 |
container_start_page |
229 |
op_container_end_page |
235 |
_version_ |
1809910644864974848 |