Detection of landscape transience using cosmogenic nuclides and topography

Abstract:

Upland landscapes are frequently perturbed by changing tectonics and climate, which can lead to temporally and spatially varying erosion rates. Hillslopes and channels respond to these changes with different rates, and the dissonance between hillslope and channel response times can be exploited to gain information about the nature and timing of landscape transience. I explore the limits to which differences between channel and hillslope processes can be used to detect transience. Slowing channel erosion rates are difficult to detect, whereas increased erosion rates can be detected if erosion rates more than double. Signals of transient erosion driven by upslope propagation of channel incision can persist for thousands to tens of thousands of years; the time perturbations can be detected is proportional to the square of the hillslope length and the inverse of the hillslope sediment transport coefficient. Climate driven (“top down”) and tectonic driven (“bottom up”) have different responses to transient perturbation, and lead to different sediment flux responses that are reflected in basinwide cosmogenic nuclide concentrations. Climate driven perturbations are mirrored in cosmogenic concentrations leaving basins whereas tectonic perturbations tend to be averaged when estimated from basinwide cosmogenics.