Since 2005, we have been studying a 1 km^2 granitic block encompassing multiple catenas. Total erosion rates calculated from nested catchment sediment samples analyzed for ^10Be range from 3.6 to 4.9 m My^-1, suggesting soil residence times of >200 ky. Along one catena, soils grade from bioturbated, light-colored, coarse-textured soils to non-bioturbated, dark-colored, texture-contrast or duplex soils--soils with sandy surface textures and clayey subsurface textures. Upper backslope soils show losses of all base cations and iron, aluminum, and silicon while lower backslope soils show enrichment (~200%) of iron, with all changes relative to parent material. Weathering products (such as exchangeable base cations) are not flushed to the Indian Ocean; instead, these precipitate out in the lowest-lying elements of hillslopes, creating saline-sodic zones. Strain calculated with soil and parent material zirconium and bulk density values shifts from negative for upper hillslope elements to positive for lower hillslope elements. Ecologically, these transitions along hillslopes create local seeps, where subsurface flowpaths are diverted to the surface. Upslope of these seeplines is sourveld or nutrient-poor vegetation, with chemical anti-herbivory defenses; downslope of these seeplines but above the barren saline-sodic zones, sweetveld or nutrient-rich vegetation dominates, with physical protection (e.g., thorns).

These long soil residence times allow differentiation of soil properties along catenas. Total erosion in this area is dominated by chemical denudation and especially so in the upper hillslope elements with high rates of infiltration. Overland flow immediately below seeplines leads to gullying in saline-sodic zones. Duplex soils are also subject to physical erosion by headcut propagation downslope of seeplines.