Quantifying variable erosion rates to understand the coupling of surface processes in the Teton Range, Wyoming

Abstract

Short-term geomorphic processes (fluvial, glacial, and hillslope erosion) and long-term exhumation control transient alpine landscapes. Long-term measurements of exhumation are not sufficient to capture the processes driving transient responses associated with short-term climatic oscillations, because of high variability of individual processes across space and time. This study compares the efficacy of different erosional agents to assess the importance of variability in tectonically active landscapes responding to fluctuations in Quaternary climate. We focus on the Teton Range, where erosional mechanisms include hillslope, glacial, and fluvial processes. Erosion rates were quantified using sediment accumulation and cosmogenic dating (bedrock and stream sediments). Results show that rates of erosion are highly variable, with average short-term rockfall rates (0.8mm/y) occurring faster than either apparent basin-averaged (0.2mm/y) and long-term ridge erosion rates (0.02mm/y). Examining erosion rates separately also demonstrates the coupling between glacial, fluvial, and hillslope processes. Apparent basin-averaged erosion rates amalgamate valley wall and ridge erosion with stream and glacial rates. Climate oscillations drive the short-term response of a single erosional process (e.g., rockfalls or other mass wasting) that may enhance or limit the erosional efficiency of other processes (glacial or fluvial). While the Teton landscape may approach long-term equilibrium, stochastic processes and rapid response to short-term climate change actively perpetuate the transient ruggedness of the topography.