SPATIAL VARIABILITY IN RIDGE EROSION SINCE THE LAST GLACIAL MAXIMUM IN THE TETON RANGE, WYOMING

Rockfalls play a significant role in shaping alpine landscapes by coupling with glacial and fluvial processes and denuding ridges. In the Teton Range, hillslope processes help shape the distinct valleys and ridges. Talus fans cover canyon floors along ridges leading to the highest peaks in the mountain range. This study quantifies hillslope processes to evaluate how ridges respond to glacial retreat and changing climate. Talus accumulation, relative surface ages on talus and ridges, and rock mass strength are used to assess the timing and controls of ridge erosion since the last glacial maximum in the Teton Range. Erosion rates are calculated with talus volume, lichen cover, weathering, and cosmogenic nuclides. Rock mass strength is measured with a Schmidt type hammer and Selby classification, which determines stability of an outcrop based on joint characteristics including spacing, width, and orientation. Erosion rates are compared to rock strength, elevation and aspect to investigate the spatial trends in hillslope failures. Talus erosion rates and surface ages vary due to joint characteristics along ridges, position in the canyon, or the pace of glacier retreat. Joints in the bedrock are more closely linked to erosion rates than the mass strength of the rock. Lower Selby rock strength classifications correlate with higher erosion rates along the ridges. Cooler temperatures below shaded, higher elevations contribute to more hillslope failures and less weathered talus materials along a north-facing ridge. Weathering on high elevation talus surfaces appeared less intense than low elevation talus fans, indicating earlier talus accumulation at lower elevations. Talus volumes also decrease at higher elevations, which also reflect less time for accumulation due to gradual glacier retreat or advances since the last glacial maximum.