Spatial variation of glacial erosion rates in the St. Elias range, Alaska, inferred from a realistic model of glacier dynamics
Abstract
Glaciers have been principal erosional agents in many tectonically active orogens throughout much of the recent geological past. The St. Elias Mountains in southeastern Alaska are a surface expression of a highly convergent, complex orogen that was likely glaciated for much of its history. We examine the Seward-Malaspina Glacier system, part of one of the largest temperate glacier systems in the world, and focus on the Seward Throat, which is a narrow passage of the glacier through the St. Elias Mountains. It is within this region that we examine the pattern of erosion where ice velocities are exceptionally high. The glacier surface velocities and elevations, which are known, provide constraints for a numerical, full-stress flowband model that enables us to infer the glacier thickness, which is not easily measured on temperate glaciers, and the corresponding sliding velocity and other basal properties. This in turn allows us to produce one of the first studies of the current spatial distribution of erosion under an active glacier; erosion rates are inferred using the flow model guided by glaciological observations and several commonly invoked erosion laws that depend upon the sliding velocity and basal shear stress. The spatial variation of current erosion rates is strongly controlled by the geometry of the glacier and less influenced by other factors, such as the equilibrium line altitude or the choice of erosion law. Inferred erosion rates are highest within the narrow, central portion of the Seward Throat, consistent with both local and regional geological observations. The numerical model used in conjunction with surface glaciological measurements is a powerful tool for investigating ice thickness, basal properties, and the spatial variation of glacial erosion rates for many temperate glaciers, where little is known aside from surface properties. The glaciological data and model results have potential use for inferring local regions of active uplift in the vicinity of the Seward Throat and for investigating the role of glacial erosion within the broader tectonic setting of the St. Elias Mountains.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMEP43D..06H
- Keywords:
-
- 0720 CRYOSPHERE / Glaciers;
- 1815 HYDROLOGY / Erosion;
- 8175 TECTONOPHYSICS / Tectonics and landscape evolution