10Be analysis of amalgamated talus pebbles to investigate alpine erosion, Garnet Canyon, Teton Range, Wyoming

Abstract

Glaciers and subsequent mass wasting events create impressive mountain landscapes; however, the ruggedness that defines these beautiful landscapes also makes it challenging to monitor erosion in the field. The result is that spatial patterns and rates of erosion in alpine landscapes are understudied. Field locations are steep and remote and hillslope processes, including rockfalls, avalanches, and landslides, are stochastic and difficult to measure directly. This study uses talus fan sediments to deepen our understanding of individual fan deposition and catchment averaged erosion processes in the alpine setting of Garnet Canyon in the Teton Range, Wyoming, USA. We measured cosmogenic 10Be concentrations from bedrock and talus deposits to compare them to volumetric estimates of erosion rates, lichen growth, and surface weathering on talus surfaces. Amalgamated pebbles from the talus deposits contained lower 10Be concentrations than any bedrock surfaces or stream sediments. The young talus surface exposure ages are all younger than 11 ka, reflecting the importance of continued rockfall activity long after glacial retreat. Only one talus fan corresponded to known seismic events. Talus deposits contribute sediments to stream systems; 10Be concentrations were lower in amalgamated talus pebbles than in amalgamated stream sands. Lichen cover, volumetric estimates of erosion rates, and 10Be concentrations showed similar spatial trends reflecting the migration of active rockfalls to higher elevations and validating the applicability of 10Be concentrations to quantify talus surface ages. Distinct 10Be concentrations on various surfaces within Garnet Canyon indicate that future work with amalgamated samples from talus deposits can contribute to investigations about landscape evolution in alpine landscapes.