Ice flow dynamics forced by water pressure variations in subglacial granular beds

TitleIce flow dynamics forced by water pressure variations in subglacial granular beds
Publication TypeJournal Article
Year of Publication2016
AuthorsDamsgaard A., Egholm D.L, Beem L.H, Tulaczyk S., Larsen N.K, Piotrowski J.A, Siegfried M.R
JournalGeophysical Research Letters
Date Published2016/12
Type of ArticleArticle
ISBN Number0094-8276
Accession NumberWOS:000392515000042
Keywordsbeneath; creep; deformation; discrete element method; glaciology; grain fracture; granular materials; rheology; sediment; sediments; sheet; slip; stick-slip; stream-b; subglacial mechanics; till; west antarctica

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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