Rates of erosion and soil accumulation

Studies of erosion rates have been another important application for in situ produced cosmogenic nuclides, since quantitative data from other methods are scarce. The earlier papers focused mainly on exposure ages and provided erosion rate estimates only as a byproduct. Craig and Poreda (1986), Kurz (1986b), and Nishiizumi et al. (1990) derived erosion rates of 8-12 m/Ma for lavas from Haleakala volcano, Maui (Hawaii), by comparing the nominal surface exposure ages with established lava ages. Sarda et al. 

1-2 m/Ma for the highest surface settings near Mt Isa (Queensland), whereas 2-5 m/Ma were typical at lower elevations. These authors also pointed out the dependence of erosion rates on rock types, being two to five times lower in silicate rocks than in limestone. 

Fleming et al. (1999) and Cockbum et al. (2000) used erosion rate determinations with cosmogenic radionuclides to assess the rates of escarpment retreat at the passive continental margins of eastern South Africa and Namibia, respectively. In both cases the retreat rates were shown to be much too low to be compatible with an escarpment origin at the continental margin during the time of continent break-up. 

Brown et al. (1995b) and Bierman and Steig (1996) developed a method to estimate mean erosion rates for entire river basins from cosmogenic nuclide concentrations in river sediment. Under the assumptions that production rates within the catchment area do not vary much, that cosmogenic nuclide concentrations are in erosion equilibrium, and that sediments are not stored for long times on the valley floor, the basin-wide erosion rate is given by 

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