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Previous models of ice–till deformation near subglacial channels or cavities neglect the fact that the motions of the two materials are coupled, and thus the interface between ice and till maynot remain stationary. Here, we analyze in succession two models which address the effect of such coupling via specification of appropriate continuityconditions for stress and velocity across the interface. The modelled scenario is that of a shallow channel–cavity, with its long axis parallel to the principal ice-flow direction, overlying actively deforming till sediments. By applying asymptotic techniques, we investigate how the pattern and velocity of the creep flow depend generallyon the ratio between the ice and till viscosities, and on the deforming-till thickness. A more sophisticated, non-linear rheology for till sediments is then introduced. It reveals that the two-way interaction between water percolation and deformation in the till will enhance the localization of sediment flow near the channel margins. The length scale over which transition of effective stress in the till takes place — from its relatively high, far-field value to the low, channel value — is found to depend critically on a dimensionless permeabilityparameter (Λ). In anycase, coupled deformation causes sediment (and ice) flow towards the channel, subsidence of the ice–till interface just outside the channel, and extension of the area over which the ice is in contact with till. Apart from having direct implications for subglacial sediment transport, these results indicate that coupled deformation can contribute significantly to the spatial evolution of stress distribution under a glacier, and thus its incorporation into future sliding and drainage theories for a soft bed should be considered essential.
The Journal of Glaciology is published six times per year. It accepts submissions from any discipline related to the study of snow and ice. All articles are peer reviewed. The Journal is included in the ISI Science Citation Index.