Assessing neotectonic activity in the Ladhiya River basin, Eastern Kumaun Himalaya using Index of relative active tectonics (IRAT)

The Ladhiya River, flowing from west to east, drains the Lesser Himalayan zone and intersects several active faults, thrusts, and lithotectonic units before merging with the Kali River at Chuki Gaon. The present study aimed to evaluate the effectiveness of geomorphic indices in assessing neotectonic activity within the Ladhiya River Basin, located in the Eastern Kumaun region of the Himalayas. Utilizing Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEM data, the total 7 watershed were delineated at a 50,000 threshold and the drainage network at a 100 threshold for detailed processing and analysis. The study focused on determining the relative tectonic activity of the Ladhiya River Basin by employing the Index of Relative Active Tectonics (IRAT), which incorporates various geomorphic indices such as Drainage Density (Dd), Drainage Texture (Dt), Hypsometric Integral (HI), Bifurcation Ratio (Br), Asymmetry Factor (Af), Valley Floor Width to Height Ratio (Vf), Stream Length Gradient (SL), and Mean Stream Length (MSL). These indices were categorized into three classes to rank each sub-basin, ultimately deriving the IRAT. The sub-basins situated on the left bank of the Ladhiya River exhibited a pronounced influence of neotectonic activity. This was particularly evident in the stream length gradient values, wherein the Dholigaon, Bigrakot, and Khatoli sub-basins display relatively high magnitudes, indicating active tectonic adjustments within these areas. The IRAT results show that areas near the trunk stream experience strong denudation, while regions farther away exhibit tectonic uplift, providing a clear picture of neotectonic activity in the Ladhiya River Basin.