SGER: Terrestrial in situ Cosmogenic Nuclides (TCN), Grain Size, and the Processes of Erosion

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Intellectual Merit: Use of terrestrial in situ cosmogenic nuclides (TCN) have emerged as a powerful technique to quantify landform-shaping processes and calculate rates of erosion. TCN concentrations in alluvial sediments can depend on the alluvial grain size sampled. This leads to problems in calculating the correct erosion rate, but also holds an underutilized potential for identifying specific hillslope and channel weathering and transport processes. This research will use TCN to quantify the hillslope processes of rock transformation into regolith, the transportation of the regolith to the channel, and grain size reduction during transport. It is both timely and attractive given that the technique is enjoying widespread acceptance by a diverse community of geoscientists. The Olympic Mountains of western Washington State and the Lemhi Range in eastern Idaho serve as diverse, but previously well-studied settings to explore the effects of variable climate, tectonics, and rock type on the grain size - TCN concentration relationship.Broader Impacts: The study will have immediate and important implications for how to estimate basin-wide erosion rates from alluvial sediment, identify the processes, spatial distribution, and rates of hillslope erosion, and apportion the various processes of erosion in numeric long term landscape evolution models. The results will have important implications for the delivery of sediment to channels and ecosystem management of the watersheds in the Olympics study area that have strong use pressures of sport fishing, Native American fish harvesting, and logging. The Lemhi Range study will be transformed into a geology field camp project which is a pioneering attempt to integrate process geomorphology into summer field programs that have largely been the domain of structure-tectonic mapping exercises. The academic training of a Ph.D. candidate, Patrick Belmont, will be supported.