The Okavango basin is an area of active diagenetic carbonate and silica accumulation. Evapotranspiration exceeds presipitation by a factor of 3 and - 96% of the incoming water is lost to the atmosphere. Evaporative concentration of dissolved solids occurs and they precipitate in the capillary fringes of islands. The less soluble components CaCO3 and SiO2 precipitate in the soils, which results in a significant volume increase which has important implications for the topography of the area and the character of the sediment fill. Geomorphology; Water chemistry.