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.