Present, past and potential denudation rates: is there a link? Tentative evidence from fission-track data, river sediment loads and terrain analysis in the South Indian shield

Ahnert [Ahnert, F., 1970. Functional relationships between denudation, relief and uplift in large mid-latitude drainage basins. Am. J. Sci. 268, 243–263] proposed that a denudation rate D could be predicted by the relation D=0.1535h, where h is local relief, a substitute for mean slope. The present study seeks to explore the value of this simple equation as a normative geomorphological tool. In two successive and complementary stages, its principles are applied to the Western Dharwar Craton of South India. First, the robustness of local relief as a reliable substitute for mean slope is examined. Following the demonstration that the equation can successfully be used in the region of interest pending correction factors for rock resistance, a potential denudation map of the Western Dharwar Craton is established. The pattern of potential denudation values is compared with known measurements of both long-term (∼102 Ma) denudation rates inferred from apatite fission track data and modern (∼10−5 Ma) denudation rates derived from available sediment load measurements in relevant river basins. Unexpectedly close similarities between long-term, short-term and potential denudation rates prompt a discussion on the merits of potential denudation as a possible standard in the appraisal of measured rates and as a tool for establishing permissible denudation rates when assessing the impact of man-induced erosion. A landscape-specific basal metabolic rate of erosion is defined as a new concept. The methodological pitfalls in extrapolating denudation rates from the measurement of sediment loads in rivers are reviewed and suggestions for tighter investigation are made.