Rapid salt weathering in the coastal Namib desert: Implications for landscape development

Data on the rate and style of breakdown on naturally occurring rock types are important to improving geomorphological understanding of landscape development in arid environments. Two years exposure of rock blocks cut from an English limestone (Bath Stone) as well as locally-relevant Namibian rocks (Karibib marble and Damara granite) within four distinctive microenvironments in and around a coastal salt pan environment reveals high rates of breakdown in the Bath Stone blocks, observable breakdown in the marble blocks, and weight gains and strength increases in the granite blocks. Breakdown is associated with high conductivities and large amounts of halite and gypsum within the surface sediments. Frequency of wetting and drying appears to be a major control on the resultant breakdown rates. These findings can be compared with recent data from further inland in the Namib desert which suggest very slow rates of breakdown of similar blocks of Damara granite and Karibib marble, even where salts are readily available. High rates of rock breakdown within coastal salt pans appear to contribute to dust production and the effective flattening of relief along the coastal strip.