Journal
GEOPHYSICAL RESEARCH LETTERS
Volume 43, Issue 23, Pages 12165-12173Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2016GL071579
Keywords
glaciology; subglacial mechanics; granular materials; sediments; creep; stick-slip
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Funding
- Danish Council for Independent Research under the Sapere Aude program
- Cecil H. and Ida M. Green Foundation
- NSF as part of the interdisciplinary WISSARD project [ANT-0838885, ANT-0839142, ANT-0636970]
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Glaciers and ice streams can move by deforming underlying water-saturated sediments, and the nonlinear mechanics of these materials are often invoked as the main reason for initiation, persistence, and shutdown of fast-flowing ice streams. Existing models have failed to fully explain the internal mechanical processes driving transitions from stability to slip. We performed computational experiments that show how rearrangements of load-bearing force chains within the granular sediments drive the mechanical transitions. Cyclic variations in pore water pressure give rise to rate-dependent creeping motion at stress levels below the point of failure, while disruption of the force chain network induces fast rate-independent flow above it. This finding contrasts previous descriptions of subglacial sediment mechanics, which either assume rate dependence regardless of mechanical state or unconditional stability before the sediment yield point. Our new micromechanical computational approach is capable of reproducing important transitions between these two end-member models and can explain multimodal velocity patterns observed in glaciers, landslides, and slow-moving tremor zones.
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