Pothole: a unique geomorphological feature from the bedrocks of Ghaghghar River, Son valley, India

Abstract

In this study, we report for the first time, the occurrence of pothole features and the processes of their development on the bedrocks of Ghaghghar River, Son valley, India. Pothole geometries were identified and measured from the middle reaches of Ghaghghar River, where it is flowing exclusively over the Rohtas limestone (a Meso-Proterozoic age) of Vindhyan Supergroup, near to the Gurma village. On the basis of field survey and remote sensing study, it has been ascertained that potholes developed in the river bed were only related to local geological and geomorphological conditions of a stream. They are mainly developed due to abrupt slope change along the river course and usually associated with intersect fractures, joints, and veins in the bedrock. The knick point of the river profile also confirms the abrupt slope change of the river in Gurma region. The river changes its course from E-W to N-S due to Markundi fault (ENE-WSW) occurring in the study area and causes the tectonic disturbances to support the development of potholes. The formations of potholes on bedrock of Ghaghghar River were generally governed by abrasion of rock fragments during high-flow regime. The geometrical dimensions of the potholes are controlled by the joints, fractures, and veins developed in bedrock of the river. The veins are typically calcitic in nature and the orientations of long axis of potholes are analogous to the trend direction of the vein. The collapse bedrocks suggest that a pothole can be formed within a short period, but cannot be fully developed and maintained for a long time in a strong incision of riverbed.

Keywords

• Ghaghghar River
• Bedrock
• Pothole
• Rohtas Limestone
• Son Valley
• India