Morphometric Analysis on Two Contrasting Litho-units of a Southern Part of West Khasi Hills District, Meghalaya, Based on Some Derived Aerial and Relief Parameters: Inferences on Neotectonism

The present study area, occupying a major south-central part of the Jadukata river basin of the West Khasi Hills District of Meghalaya, predominantly comprises two contrasting litho-units viz., the Precambrian gneissic unit (PGU) towards the north of the study area and the Mahadek Formation constituted of sedimentary rocks (MFS) in the south. Derived areal and relief morphometric parameters have been analysed on five sub-basins two of which are in the PGU (Umlang and Umkyrtha) and the other three (Umsophew, Wah-Phodthra, and Khandow) predominantly in the MFS. The drainage density (Dd) and stream frequency (Fs) values are relatively lower for the sub-basins of PGU suggesting higher overland flow. This is substantiated by higher values of the constant of channel maintenance (C) and length of overland flow (Lg). The relief ratio (Rr) and ruggedness number (Rn) are higher for the sub-basins of MFS implying more dissection. High hypsometric integral (HI) and pseudo-hypsometric integral (PHI) suggest youthful stage and neotectonic rejuvenation with a tilt towards the west as indicated by asymmetry factor (AF) and topographic profile. Association of distinct knickpoints of longitudinal profiles with prominent lineaments indicates active fault. Preferred orientation of lower order streams in the PGU sub-basins suggests neotectonism. Deep incision by Umsophew, Wah-Phodthra, and Khandow rivers, forming V-shaped valleys through the MFS is the result of neotectonic uplift which has been further substantiated by very low valley floor-to-height ratio (Vf) at nearby locations of the confluence of these rivers with the Kynshi.