Basal hydrofractures near sticky patches

Basal crevasses are macroscopic structural discontinuities at the base of ice sheets and glaciers. Sticky patches (also referred to as sticky spots) are regions of high basal shear stress caused by low subglacial water pressure or topographic high of the bedrock. Motivated by observations, we hypothesise that in the presence of basal water pressure, spatial variations in basal shear stress on the sticky patches can promote and localise basal crevassing. In the theoretical context of linear elastic fracture mechanics, we develop a model evaluating the effect of shear stress variation on the growth of basal crevasses, finding that the existence of sticky patches can promote mixed-mode basal crevassing on the downstream end. By simulating the quasi-static growth of such mixed-mode basal crevasses, we find that such crevasses tend to incline upstream and propagate along a specific path, which can be approximated by the principal stress trajectories in the uncracked ice. A detailed exploration on the dimensionless parameter space indicates that the crevassing is controlled by three parameters—the flotation fraction, the relative magnitude of excess shear stress, and the relative size of the sticky patch. Inspired by the crevassing in the elastic model, we also explore the propagation of basal crevasses using the viscoelastic rheology.