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...
Published in: | Annals of Glaciology |
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Main Authors: | , , , , |
Format: | Text |
Language: | unknown |
Published: |
ScholarWorks at University of Montana
2000
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Subjects: | |
Online Access: | 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 |
Summary: | 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. |
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