Till flux dependence on effective pressure

Deformation of subglacial sediment during basal slip shapes the beds of many fast-flowing glaciers and ice streams. The resultant sediment flux impacts glacier dynamics and rates of subglacial erosion over a range of timescales, but its fundamental dependencies are not well understood. Using a cryogenic ring shear device, we conducted a suite of experiments to investigate the effects of both effective normal stress and slip speed on rates of till transport. Sediment fluxes were computed using digital image correlation from a photographic time series of the till bed. We find a near linear relationship between sediment flux and slip speed, but a non-monotonic, double-valued dependency of sediment flux on effective stress. Deformation primarily occurred in a narrow shear band near the ice sole, the thickness of which could vary with both parameters. Coupling between ice and till increased at higher slip speeds and effective stresses and scaled the magnitude of the flow profile.