Original paper

Badland formation along the Pravara River, Western Deccan, India. Can neotectonics be the cause?

Joshi, Veena U.; Nagare, Vikas B.

Abstract

The rill and gully erosion is the most severe form of soil erosion in India, giving rise to the development of badland topography. A large part of India is infested by ravines or badlands that are mostly confined in the northern parts of the country where Indo Gangetic Plains lie. Unlike the northern parts, south central part of India, especially the Deccan Trap Region is characterized by an erosional landscape and there is dearth of sediments everywhere. Alluvial sediments are found only along the narrow zones of the river banks and patchy colluvial sediments are found along the foothills of a few watersheds. Badlands have been formed along some of these deposits. Due to the human activities in the past few decades, the rate of land degradation and badland development is increasing at an alarming rate all over the world. In India also reclamation of land for the purpose of agriculture has become a common trend. The study area is a natural badland area which is presently suffering from heavy sediment losses every year, due to recent activities of men. Very few studies have been conducted on these badlands and the evolution of these badlands has remained a question. Therefore, a deeply dissected badland topography along the banks of Pravara River and its tributaries in the Western Deccan Province has been investigated in the present study in order to understand its mode of origin. Few previous studies postulated that badlands in the Western Deccan Upland Region owe their origin to the Pleistocene-Holocene climate change events. The model is best applied in the foothill badlands but the mode of occurrence of small patches of badlands along some of the riverbanks give benefit of doubt about the climate change as their origin. Along the footslopes, the ravines are continuous and occupy a large area but along the riverbanks they occur in small patches and their occurrence do not seem to follow any distinct principle of geomorphology. They abruptly start at an unexplained spot, continue downstream for a few km and abruptly disappear, without any explanation of its sudden disappearance. In order to evaluate the tectonic stability of the area which could have been an alternative explanation for their origin, few geomorphic indices, such as Mountain Front Sinuosity Indices (Smf), Basin Asymmetry (AF), Stream Length Gradient Index (SL index) and Valley Floor to Width Ratio (Vf) were calculated. Results indicate that the area under investigation had been affected by moderate tectonism in the past. The badlands that are found in small pockets along the riverbanks in the study area were initiated by such tectonic events. The area is crisscrossed by dense network of lineaments and the badlands mostly lie along those lineaments. During some of the past tectonic events, lineament controlled 'block or local uplift' have affected these areas, causing local drop in the base-level, hence promoting erosion along these points to form the ravines. The essential point is that a combination of morphometric variables and a simple lineament analysis suggest that a neotectonic interpretation of apparently randomly spaced badlands development in the Western Deccan is more probable than a paleoclimatic or anthropogenic interpretation.

Keywords

badlandtectonismlineamentpleistoceneholocenedeccan