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Shear dilation of subglacial till results in time-dependent sliding laws

Published version
Peer-reviewed

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Authors

Neufeld, JA 

Abstract

jats:pThe dynamics of glacial sliding over water-saturated tills are poorly constrained and difficult to capture realistically in large-scale models. Experiments characterize till as a plastic material with a pressure-dependent yield stress, but the subglacial water pressure may fluctuate on annual to daily timescales, leading to transient adjustment of the till. We construct a continuum two-phase model of coupled fluid and solid deformation, describing the movement of water through the pore space of a till that is itself dilating and deforming. By forcing the model with time-dependent effective pressure at the ice–till interface, we infer the resulting relationships between basal traction, solid fraction and rate of deformation. We find that shear dilation introduces internal pressure variations and transient dilatant strengthening emerges, leading to hysteretic behaviour in low-permeability materials. The result is a time-dependent effective sliding law, with permeability-dependent lag between changes in effective pressure and the slidingspeed. This deviation from traditional steady-state sliding laws may play an important role in a wide range of transient ice-sheet phenomena, from glacier surges to the tidal response of ice streams.</jats:p>

Description

Peer reviewed: True

Keywords

subglacial till, glacier dynamics, basal sliding

Journal Title

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences

Conference Name

Journal ISSN

1364-5021
1471-2946

Volume Title

Publisher

The Royal Society
Sponsorship
NERC (NE/L002507/1)