Shear-Layer Thickness and Structure Evolves With Effective Stress in Subglacial Environments

Abstract

Moving glaciers shear and deform the subglacial till beneath them, with deformation concentrated in a thin shear-layer. This shear-layer's properties are partially controlled by effective stress, which depends on ice thicknesses and subglacial hydrological networks. Understanding the relationship between effective stress and shear-layer thickness helps characterize basal resistance to ice motion and inform subglacial landform formation. While experiments agree increasing effective stresses beget decreasing shear-layer thicknesses at high effective stresses, a trend is unclear at low effective stresses. Continuum models predict that increased effective stresses yield increasing shear-layer thicknesses, inconsistent with experiments. Here, we identify how properties of a medium's persistent contact network lead to non-monotonic shear-layer thicknesses in effective stress through Discrete Element Method simulations. We find effective stress can alter both shear-layer thickness and structure, and thereby depth-averaged friction. We integrate these insights into an existing continuum model by modifying its yield parameters, resolving inconsistency between model and experiment.