Processes of Alpine Glacial Erosion in the Sierra Nevada, California, and the Wind River Range, Wyoming

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Glacial erosion is accomplished by quarrying of rock from rough edges of the subglacial bed, and abrasion of rock that smoothes and polishes the bed. Yet there is little quantitative data how rock hardness and the degree of rock fracturing govern quarrying and abrasion processes. Preliminary work in the granitic landscape of Yosemite National Park suggests that the pace of glacial landscape evolution and the spatial pattern of erosion are controlled by the spacing of fractures in the rock. This study will improve knowledge of glacial erosion by employing two natural experiments in the Sierra Nevada and the Wind River Range of Wyoming. Variations in fracture spacing are common in the crystalline plutons of Yosemite Park, whereas in the Wind River Range glaciated terrain incudes both crystalline and sedimentary lithologies. Cosmogenic 10Be measurements of glacial polish samples collected along longitudinal valley profiles will constrain the depth of glacial erosion, and the history of deglaciation. Interpretation of field data will rely upon 1D and 2D numerical glacial models. These models will simulate the evolution of the longitudinal valley profile in the face of the measured contrasts in bedrock erodibility, explictly accounting for both quarrying and abrasion, and they will track basal sediment content and size distribution, allowing testing against observed patterns of both erosion and distribution of coarse sediment.This project is designed to document the specific controls on glacial erosion. With few exceptions, the importance of rock properties in controlling styles and rates of erosion in the landscape has not received much attention in the past. The study sites are in areas where glacial features are prominent, and the influence of rock properties can be ascertained. This problem is important because glacial processes have shaped much of the modern landscape of North America, and changing climates may affect the degree of glacial erosion. The study site in Yosemite National Park also provides opportunity to take the science directly to the public in outreach activities that take advantage of the high volume of visitors and strong collaborative ties to park staff.