Quantifying denudation rates on inselbergs in the central Namib Desert using in situ-produced cosmogenic 10Be and 26Al

In situ-produced cosmogenic isotope concentrations in bedrock surfaces provide valuable estimates of site-specific, long-term rates of denudation and provide constraints for numerical landscape evolution models. Measurements of cosmogenic Be-10 and Al-26 from granite inselbergs in the arid to hyperarid central Namib Desert, Namibia, indicate a mean rate of summit lowering of 5.07 +/- 1.1 m/m.y. over the past greater than or equal to 10(5) yr. The persistence of an arid climate in the region suggests that a similar rate may have prevailed for the past similar to 10 m.y. and possibly throughout much of the Cenozoic. Some samples have complex exposure histories that can be explained by the mode of inselberg weathering and mass wasting. The denudation rates estimated here are an order of magnitude higher than those reported for inselbergs in a significantly more humid environment in South Australia. This difference may largely be due to active salt weathering in the central Namib as a result of high levels of coastal fog precipitation.