DIGGING WITH RHINOS: SOIL PRODUCTION AND TRANSPORT ACROSS AN EQUILIBRIUM LANDSCAPE

Soil-mantled hillslopes are extensively used to understand the soil development and pedogenic processes active in landscapes around the world and across a wide range of climate zones. Here, we quantify soil production and transport processes across three different climate zones in Kruger National Park, South Africa. Uniform granite lithology and previous work examining pedogenic profiles, landscape morphology, and the role of termites on savanna hydrogeomorphology for these landscapes enable us to gain unique insight into the processes shaping an slowly eroding equilibrium landscape. Low catchment averaged erosion rates (3-7 m/Ma) that do not vary by climate zone are balanced roughly by uniform soil production rates beneath soil mantles ranging from 50 cm to 3.5 m thick. Soil production rates are quantified using in situ produced cosmogenic ¹⁰Be from in-place weathered bedrock beneath the soil (regolith) and show no systematic relationship with overlying soil thickness. Soil production rates range from about 2 to 8 m/Ma. Depth profiles of ¹⁰Be concentrations reveal concentrations in stone lines at intermediate depths that are up to about an order of magnitude greater than predicted by simple attenuation of ¹⁰Be production with depth. Depth profiles of ¹⁰Be from our deepest pit (3.5 m) help quantify the collapse of saprolite under long-term solution removal of mass. We use these concentrations, landscape morphometry, and a simple sediment transport model accounting for termite bioturbation to infer downslope transport rates. These remarkably slow soil production and transport processes help explain the deep weathering profiles previously quantified for this landscape and the downslope presence of a seep line associated with landscape scale clay accumulation.