Physical Geography seminar: What lies beneath? Subglacial processes under cold ice
Dr Sean Fitzsimons from the Department of Geography, University of Otago, New Zealand
Thermal and mechanical processes that operate beneath glaciers govern the interactions between ice, water and the glacier bed. These processes regulate glacier flow and determine the processes of erosion, transportation and deposition. This presentation will review recent studies of debris entrainment and deformation at the base of cold-based glaciers in the McMurdo Dry Valleys.
The review will focus on measurements and observations in tunnels and at the margins of glaciers that rest on ice-rich permafrost. These data show that the basal zones of the glaciers are characterised by blocks and layers of frozen sediment that have been eroded and entrained from the glacier beds. The blocks of sediment experience negligible internal shear but they rotate and become fractured as they are entrained and transported in basal ice. Although all the beds are below -18*C sliding occurs between ice and frozen sediment, which, together with thin bands of high shear, results in further erosion and entrainment of particles. The observed patterns and process of erosion and entrainment suggest the basal décollement of the glaciers are within the frozen sedimentary substrate rather than at the glacier ice-substrate boundary.
The resulting pattern of subglacial strain bears a striking resemblance to subglacial deformation in warm-based glaciers that rest on deformable substrates. These results challenge conventional notions of the dynamics and geological activity associated with cold-based glaciers.