Abstract:
Slip along the fault where glacier ice at its pressure-melting temperature rests on a bed consisting of rough rock (hard bed) or deformable sediment (soft bed) is responsible for fast glacier flow and for most of the glacial contribution to sea-level rise. Numerical models of fast glacier flow yield results that are acutely sensitive to the form of the slip law that relates drag at the beds of glaciers to their slip velocity and basal water pressure. To test slip-law hypotheses, we conduct laboratory experiments in which a ring of ice at its pressure-melting temperature is rotated over idealized hard and soft beds. We also use a numerical model of glacier slip applied to measured hard-bed topographies in the Swiss Alps and Canadian Rockies to upscale results and consider effects of three-dimensional, non-periodic topography. Results indicate that for both hard and soft beds drag increases to a limiting value over a small range of increasing slip velocity or basal water pressure and remains at that value over most of the relevant parameter space, consistent with Coulomb behavior. These results point to a universal slip law that would simplify and improve estimations of glacier discharges to the oceans.
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