Erosion of an Ancient Mountain Range, the Great Smoky Mountains, North Carolina and Tennessee

Matmon, Ari; Bierman, Paul; Larsen, Jennifer; Southworth, Scott; Pavich, M; Finkel, Robert; Caffee, M

n resnsport,uggest that most of the cosmogenic nuclide inventory in sediments is accumulated while they are eroding from bedrock and traveling down hill slopes. Spatially homogeneous erosion rates of 25 - 30 mm Ky1 are calculated throughout the Gred concentrations of cosmogenic d from alluvial sediment. 10Be ants collected from headwater trih an average erosion rate of 288mmKy1, similar to that of the nt out of the mountain range. Grain-size-specific analysis of 6 smaller grain sizes than in larger ones. The difference in concentrations arises from the largelarge grains. Large sandstone clasts disaggregate into sand-size only clasts from the lower parts of slopes reach the streams. 2r samples. However, alluvial samples have lower 26Al/10Be ratiosonger integrated cosmic ray exposure history that includes perio such as the reduction of relief through slope processes, and of Hack’s dynamic equilibrium model such as the similarity of eroshe Appalachians, we conclude that rates of erosion, integrated over varying time periods from decades to a hundred million years are similar, the result of equilibrium between erosion and isosABSTRACT: Analysis of 10Be and 26Al in bedrock (n10), colluvium (n5 including grain size splits), and alluvial sediments (n59 including grain size splits), coupled with field observations and GIS analysis, suggest that erosion rates in the Great Smoky Mountains are controlled by subsurface bedrock erosion ad diffusive slope processes. Theults indicate rapid alluvial tra minimal alluvial storage, and seat Smoky Mountains using measur10Be and 26Al in quartz separatend 26Al concentrations in sedimebutaries that have no upstream samples (n18) are consistent witoutlet rivers (n16, 246mmKy1), which carry most of the sedimealluvial sediment samples shows higher nuclide concentrations in elevation distribution of the source of the smaller grains compared with the narrow and relatively low source elevation of the grains rapidly during weathering and downslope transport; thus,6Al/10Be ratios do not suggest significant burial periods for ou than bedrock and colluvial samples, a trend consistent with a lds of burial during down-slope transport. The results confirm some of the basic ideas embedded in Davis’ geographic cycle model,ion rates across different lithologies. Comparing cosmogenic nuclide data with other measured and calculated erosion rates for ttatic uplift in the southern Appalachian Mountains.