Soils and climatic geomorphology on the Karnataka plateau, peninsular India

Abstract As a result of extensive field reconnaissance in southern India, a geographical traverse across the planation surface of the Karnataka uplands, which lie in the rainshadow of the Western Ghats, was selected to assess the consequences of a steep rainfall gradient on soil and landform patterns. The study of the traverse, described in detail, reveals a characteristic progression of soil type and wash divide form from the high-rainfall to the semi-arid end of the continuum and invites a critical reappraisal of classical notions in climatic geomorphology and the soil sciences. The assumption that alternations of wet and dry climates are necessary to achieve planation is given special consideration, and the often held belief that kaolinite minerals are diagnostic of humid palaeoclimates when found in a semi-arid climate is challenged. The findings for the Indian traverse are set against the better known data for West Africa, where the rainfall range between the Gulf of Guinea and the Sahel is comparable with that observed in the south-western Deccan. Differences outweighing similarities, attention is drawn to the possibility that tectonic regime, which also controls the degree of landscape stripping, is a major key to understanding the climatic geography of soils, the tread of planation surfaces and the shape of hillslopes from one region of the Tropics to another.