Impact of Interfacial Friction at the Ice-Bed Boundary on Glacier Sliding

Abstract

Current theories for describing glacier sliding over hard beds assume that basal drag is entirely due to normal forces acting on meter-scale bed roughness and neglect tangential friction at the ice-bed interface. However, this interfacial friction is likely to account for a significant proportion of basal drag in the presence of basal debris or cold ice, and may render current sliding theories inaccurate. The aim of the study is to evaluate if current sliding laws still apply in the presence of interfacial friction. We propose a simplified analytical model of glacier sliding controlled by both ice creep around bed irregularities, as proposed by Weertman (1957, https://doi.org/10.3189/s0022143000024709), and interfacial friction at the ice-bed boundary determined by Coulomb dependency. We show that reduced sliding speed from additional interfacial friction is mitigated by increased ice deformation near the bed, which occurs as a result of additional basal deviatoric stresses reducing the effective viscosity. We further generalize these results using a numerical model of glacier sliding over a sinusoidal bed, capable of simulating cavity formation and basal sliding with several formulations of interfacial friction. We find that the additional friction generally does not modify the form of previously proposed friction laws but significantly increases the maximum resistive shear stress of the bed. These results suggest that friction laws that are commonly used in ice-sheet models and whose parameters are empirically optimized, could be still used in circumstances where interfacial friction is non-negligible.