Geological and Atmospheric Sciences
Journal or Book Title
Journal of Glaciology
A new ring-shear device allows basal slip and related processes to be studied in laboratory experiments for the cases of hard or soft beds. The device rotates a confined ring of ice (0.9 m outside diameter) across a horizontal bed at a constant velocity or drag, while a vertical stress is applied and basal water pressure is controlled. A bath with circulating fluid regulated to ∼0.01°C surrounds the ice chamber and keeps the ice at its pressure-melting temperature. In a first experiment with a stepped rigid bed and zero basal water pressure, steady lengths of step cavities depended upon slip velocity raised to a power of 0.59, in general agreement with the square-root dependence of some models of sliding and linked-cavity hydraulics. Transient cavity growth after slip velocity increases was not monotonic, with damped volume oscillations that converged to a steady value. Once ice separated from lee surfaces, drag on the bed was constant and independent of slip velocity and cavity size, consistent with a shear-stress upper bound like that indicated by sliding models. Shear strains near the bed exceeded 30 and ice developed multiple-cluster c-axis fabrics similar to those of sheared ice in temperate glaciers.
Creative Commons Attribution license.
International Glaciological Society
Iverson, Neal R. and Petersen, Ben B., "A new laboratory device for study of subglacial processes: first results on ice–bed separation during sliding" (2011). Geological and Atmospheric Sciences Publications. 148.