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Nicolaj Krog Larsen

Creep and stick-slip in subglacial granular beds forced by ocean tides

Publikation: KonferencebidragKonferenceabstrakt til konferenceForskning

Observations show that the flow velocity of several marine-terminating glaciers and ice streams are strongly linked to tidal stage. Deformation of subglacial sediments often accounts for much of the flow, but the mechanical behavior of the sediment remains poorly understood. Measurements and laboratory experiments provide important constraints, but existing models have not been able to explain the internal processes driving transitions from stability to stick-slip within the sediment. In this presentation we use a coupled numerical model of grain and fluid dynamics to show that rapid rearrangements of load-bearing force chains within the granular sediments drive the mechanical transitions. Cyclic variations in driving stresses or pore-water pressure, caused by ocean tides, give rise to strain-rate dependent creeping motion at stress levels below the point of failure, while disruption of the force-chain network induces fast strain-rate independent flow above it. This finding contrasts previous descriptions of subglacial sediment mechanics, which either assume a rate-dependent rheology regardless of mechanical state or unconditional stability before the sediment is stressed to a yield point. Our new micro-mechanical computational approach is capable of reproducing important transitions between these two end-member models, and it can explain multimodal velocity patterns observed in marine-terminating glacier and ice stream systems.
StatusUdgivet - 2016
BegivenhedInternational Glaciological Meeting: International Symposium on Interactions of Ice Sheets and Glaciers with the Ocean - Scripps Institution of Oceanography, La Jolla, USA
Varighed: 10 jul. 201615 jul. 2016


KonferenceInternational Glaciological Meeting
LokationScripps Institution of Oceanography
ByLa Jolla

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