ALBERT

Description: The determination of basin-averaged denudation rates from cosmogenic nuclide concentrations in stream sediments depends on the surface production rate, scaling methods of cosmic ray intensities, and the correction algorithms for skyline, snow and vegetation shielding. While much work has been devoted to the calculation of skyline shielding factors (Dunne et al. 1999, Codilean 2006), the pitfalls of and potential solutions to the derivation of skyline shielding factors for large areas has never been addressed. Specifically, the resolution of common topographic datasets, 30 to 90 m, are coarse enough that significant underestimations, up to nearly 20 percent, of the shielding factor can occur. This effect is greatest in mountainous regions with high relief, i.e. exactly those landscapes which are most often studied with cosmogenic methods. By combining measurements of surface roughness from high resolution topographic data with cosmogenic ray shielding laws, we determined an empirical model for the calculation of accurate skyline shielding factors. Codilean A. 2006. Calculation of the cosmogenic nuclide production topographic shielding scaling factor for large areas using DEMs. Earth Surface Process and Landforms 31: pp. 785-794. Dunne J, Elmore D & Muzikar P. 1999. Scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces. Geomorphology 27: pp. 3-11.