An integrated geomorphological and geophysical study of neotectonic activity: Analysis of heavy siltation in the Chilka Lake of Odisha, India

Abstract

The present study investigates the reasons for the heavy siltation in Chilka Lake which is analysed by satellite imagery, ground survey and geophysical studies. Modified normalized difference water index (MNDWI) and linear spectral unmixing method (LSU) reveal the presence of a wetland, suspended sediments and aquatic weeds along the northeastern boundary of the lake and beyond. Gravity, magnetic data and 3D inversion modelling reveal various sets of faults that were periodically reactivated to form uplifted and subsided blocks around the lake. Geomorphic evidence like low valley width/height ratio (Vf) with <1.5 (valley undercutting due to uplift), low mountain front sinuosity index (Smf), basin asymmetry, transverse topographic symmetry (T), compressed meanders, and flow diversion are all indicative of neotectonic activity and the resulting reactivation of faults. Neotectonic activity is also evidenced from the occurrence of seismic tremors in and around the Chilka region which lies in Zone III of the seismic zonation map of India. This neotectonic activity can be related to the compressional stresses persisting over most parts of the Indian Shield due to the Himalayan Orogeny. The resulting uplift and subsidence led to erosion of the uplifted block and sedimentations in the subsided block by the rivers Daya and Bhargabi. This is the probable cause of heavy siltation in Chilka Lake, where the eroded sediments of the uplifted block are deposited by these two rivers. This work reveals an interconnection between geomorphic features and subsurface structures that together control neotectonic activity in the Chilka region. Compressive stresses related to the Himalayan Orogeny reactivate ancient NW–SE and NE–SW trending faults, resulting in uplift and subsidence of basement blocks. Recent sedimentation is controlled by these basement uplifts and depressions. Uplifts trigger river erosion, transferring large volumes of sediment into the Chilka Lake depression. Organic nutrients transported with the sediments are responsible for the enhanced growth of aquatic weeds in the northeastern part of Chilka Lake. This work reveals an interconnection between geomorphic features and subsurface structures that together control neotectonic activity in the Chilka region. Compressive stresses related to the Himalayan Orogeny reactivate ancient NW–SE and NE–SW trending faults, resulting in uplift and subsidence of basement blocks. Recent sedimentation is controlled by these basement uplifts and depressions. Uplifts trigger river erosion, transferring large volumes of sediment into the Chilka Lake depression. Organic nutrients transported with the sediments are responsible for the enhanced growth of aquatic weeds in the northeastern part of Chilka Lake.