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Basal mechanics of Ice Stream B, west Antarctica: 1. Till mechanics

Tulaczyk, Slawek and Kamb, W. Barclay and Engelhardt, Hermann F. (2000) Basal mechanics of Ice Stream B, west Antarctica: 1. Till mechanics. Journal of Geophysical Research B, 105 (B1). pp. 463-481. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:20140522-090055760

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Abstract

Data from laboratory geotechnical tests on till recovered from beneath Ice Stream B, West Antarctica, at the Upstream B camp (hereinafter the UpB till) show that failure strength of this till is strongly dependent on effective stress but is practically independent of strain and strain rate. These data support use of a Coulomb-plastic rheology in modeling of ice stream behavior and subglacial till deformation. Our testing program combined triaxial, ring shear, and confined uniaxial tests to investigate till strength and compressibility. Results show that the UpB till follows closely Coulomb's equation in which shear strength is a linear function of normal effective stress (apparent cohesion near zero and internal friction angle ϕ equal to 24°). Till compressibility is best described by a logarithmic function that relates void ratio to normal effective stress. In general, the behavior of the UpB till is consistent with other experimental evidence regarding mechanical behavior of granular materials. Based on our laboratory results we formulate the Compressible-Coulomb-Plastic till model in which there are three interrelated, primary state variables: shear strength, void ratio, and normal effective stress. This model is used in the second part of our study to simulate response of subglacial till to realistic effective stress forcings. These simulations demonstrate that the model is capable of reproducing fundamental aspects of subglacial till kinematics: (1) occurrence of tilt rate oscillations and negative tilt rates in tiltmeter records, and (2) distributed till deformation to depths of 0.1–1.0 m beneath the ice base. Our laboratory and modeling results substantiate application of the Compressible-Coulomb-Plastic model in simulations of the motion of Ice Stream B over its weak till bed.


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http://onlinelibrary.wiley.com/doi/10.1029/1999JB900329/abstractPublisherArticle
http://dx.doi.org/10.1029/1999JB900329DOIArticle
Additional Information:© 2000 American Geophysical Union. Manuscript Accepted: 20 Jul 1999. Manuscript Received: 6 Aug 1998. Revised March 3, 1999. Paper number 1999JB900329. This project was funded by grant OPP-9219279 from the National Science Foundation to B. Kamb and H. Engelhardt. Ronald F. Scott of the Division of Engineering and Applied Science at the California Institute of Technology has generously contributed equipment and expertise at many stages of this project. His help was especially vital during the design and construction of the ring shear device. We are thankful to Less Fruth and the management of Earth Technology, Inc., Irvine, California, for making available their triaxial testing laboratory. This paper benefited from helpful comments provided by Neil Humphrey, Neal Iverson, and Joseph Walder.
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Funding AgencyGrant Number
NSFOPP-9219279
Record Number:CaltechAUTHORS:20140522-090055760
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140522-090055760
Official Citation:Tulaczyk, S., W. B. Kamb, and H. F. Engelhardt (2000), Basal mechanics of Ice Stream B, west Antarctica: 1. Till mechanics, J. Geophys. Res., 105(B1), 463–481, doi:10.1029/1999JB900329.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45881
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:27 May 2014 17:10
Last Modified:13 Sep 2016 23:20

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