Review of subglacial hydro-mechanical coupling: Trapridge Glacier, Yukon Territory, Canada

Abstract

The interaction of basal processes with the subglacial drainage system is a critical issue in understanding glacier dynamics. Since the recognition that many glaciers and ice masses overlie soft sediments rather than hard bedrock, much research has been undertaken to investigate how mechanical and hydrological conditions of a deformable substrate control the coupling at the ice–bed interface and thus affect fast ice flow and glacier surging. In research undertaken on Trapridge Glacier, a small surge-type glacier in the St. Elias Mountains, Yukon Territory, Canada, we have combined extensive field investigations using novel measurement techniques and theoretical modelling to study hydro-mechanical coupling processes. Measurements of subglacial water pressure indicate that the basal water system can be dramatically inhomogeneous, both spatially and temporally. Since ice–bed coupling is strongly influenced by subglacial water pressure, the stresses at the bed are also markedly heterogeneous and are expected to form a patchwork distribution which mimics the pressure distribution of the basal water system. This heterogeneity in the stress field at the ice–bed interface introduces a pronounced variability to the basal motion mechanics. As such, basal sliding and subglacial sediment deformation are not steady and continuous processes. Instead, the variability of the subglacial water system leads to a spatial and temporal interplay of increased ice–bed coupling at low water pressures at one site or time with ice–bed decoupling during rising water pressures at other sites or times. Thus, on the one hand there is downglacier shear deformation of the bed and accumulation of elastic strain in ice and sediment, while on the other hand there is enhanced slip-sliding of the glacier and upglacier shear motion of the bed due to an elastic relaxation of the sediment.