Mapping subglacial geomorphology and structure in a collisional orogen: an example from the Malaspina Glacier, Alaska

The Malaspina Glacier of Southern Alaska /Yukon Canada provides the opportunity to investigate the interaction between glaciers and tectonics, in an active orogen that is forming from the collision and accretion of the Yakutat Microplate in the Gulf of Alaska. Several large alpine glaciers coalesce on the piedmont of the Saint Elias Mountains to form the Malaspina Glacier. We use feature tracking by cross correlation of Landsat satellite images to map the velocity and strain rate fields on the surface of the Malaspina Glacier to explore how the structural geology at the bed of the glacier affects the dynamics and structure of the moving ice on the surface. Rates of flow in alpine areas are fast and ice can move 90+ m/month in the summer and on the piedmont ice can move over 100-300 m a year. Strain rates calculated from the velocity fields are on the order of 10^-9 / s on the surface of the glaciers. Strain rate maps reveal the nature of the stress field in the ice where it moves over topographic features at the bed of the glacier. The results bear directly on the origin of ice falls that originate at thrust faults on the limbs of large folds, the origin of fast glacier flow along fault zones where rheology at the bed of the glacier is presumably impacted by rapid erosion and development of weak water saturated till, the pattern of ice flow around the termination of a large strike slip fault, and the presence and extent of subglacial lakes and distributary channels that feed outburst flooding at the terminus of glaciers. The morphology and dynamics of the Malaspina piedmont lobes also provide insight into the strike slip component of motion along the Esker Creek Fault that was activated during an M 8.1 earthquake in 1899, as well as some control on the basal topography, and perhaps structural geology, where the Fairweather Transform Fault and Aleutian Megathrust are currently linking together beneath the Malaspina Glacier.