Glaciers can move by unstable “stick-slip” at their beds, causing abrupt increases in glacier velocity and teleseismicity. For stick-slip to occur, the slip surface must be capable of healing (i.e., becoming stronger) between periods of rapid slip, so that stress can be recharged. We investigate subglacial healing mechanisms for soft-bedded glaciers with slide-hold-slide experiments using two different ring-shear devices. In these experiments, slip is initiated after varied intervals of static contact (hold times). In one set of experiments, till alone was sheared, whereas in another set, ice at its pressure-melting temperature was slid over till. Comparison of data from the two experiments indicates that at shorter hold times in the ice-till experiments, basal shearing resistance was limited by slip at the ice-bed interface. However, with sufficient hold time (∼1 day), the interface strengthened enough so that displacement occurred by shearing of the till bed. A simple model that relates healing at the interface to changes in the real area of contact (Ar) between the ice and bed matches the observations well. The model attributes growth of Ar to pressure-enhanced melting along grain surfaces that closes micro-cavities spanning grains at the ice-bed interface.

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