TOPOGRAPHIC FINGERPRINTS OF MICRO-CLIMATE AND LITHOLOGY IN THE CENTRAL APPALACHIANS

To elucidate the roles of climate, tectonics, and lithology in controlling topographic evolution in the central Appalachians, we combine high resolution, LiDAR-derived digital topography and the cosmogenic radionuclide ¹⁰Be to measure rates of regolith transport and erosion. We employ these to test transport rules at the Shale Hills Critical Zone Observatory (SSHO) and 27 other first-order watersheds in the Susquehanna River Basin (SRB). Our results from SSHO imply that subtle differences in insolation between north- and south-facing slopes impact the frequency of dilational regolith transport processes (e.g., freezing-thawing cycles), which in turn modulates the efficiency of regolith production and downslope transport. As a result, lower hillslope gradients evolve on south-facing hillslopes as compared to their north-facing counterparts. Despite this asymmetry, mass fluxes are equivalent on north- and south-facing hillslopes, and correspond with catchment-wide lowering rates of 20 – 30 m/My. Comparisons of ¹⁰Be-derived erosion rates with ridgetop curvature measurements suggest near-equilibrium topography at SSHO. Comparison of ¹⁰Be-derived erosion rates and ridgetop curvature measurements at other watersheds in the SRB suggests that regolith diffusivity is similar on ridgetops formed in Piedmont schists, Valley and Ridge shales, and Valley and Ridge sandstones. Watersheds in the Appalachian Plateau, however, exhibit characteristics of a recent transient increase in erosion rate, indicating that ridgetop curvature and erosion rates are out of equilibrium. Our results suggest that tectonic influence persists in the Appalachian Plateau, where elsewhere the history of periglacial climate sets topographic expression.