This paper focuses on the analysis of geomorphic landform development, particularly between the Trans Himadri Fault and the Main Central Thrust including Berinag Thrust and other major NNE–SSW and NW–SE striking faults/thrusts in the Higher Central Kumaun Himalaya. Digital analysis of remote sensing data, field investigations including drainage analysis, and development of landforms have been carried out to understand the morphotectonic evolution and, thereby, the neotectonics in this region. A number of morphometric indices [(stream length‐gradient index (SL), steepness index (ks), Chi (χ)] were computed together with knick point analysis. Offsetting of the major river and tributaries was observed along a NNW–SSE direction. Other tectonic landforms, including truncated saddles and disturbed terrace patterns, show that the area is presently undergoing active deformation. The valley floor morphology in the vicinity of the major thrusts provides evidence for aggradation of recent fluvial activity. Developments of various neotectonic features, such as starth terraces, off‐streams, truncated saddles, disrupted terraces, and palaeolake deposits, are evidences for recent tectonic activities associated with the major thrusts/faults. Cut‐and‐fill terraces with thick alluvial cover, debris‐flow terraces, and alluvial fan terraces are significant aggradational landforms observed within the valley that provide signatures of past climatic records. Our study reveals that the fluvially modified debris‐flow terraces were formed between 5 and 20 ka. We infer that the major phase of valley‐fill happened between 5 and 12 ka, whereas the youngest phase of aggradation may have responded to the Holocene tectonic activity that took place around 5–6 ka. The study is significant to understand the recent geomorphic development and tectonic deformation in the study area and may be helpful for future infrastructural development in the region.
We have analysed the geomorphic signatures in aggregation with the geomorphic indices with respect to hinterland and foreland neotectonic variability across the major Himalayan thrust system along the Kali River valley of eastern Kumaun Himalaya. The valley floor morphology in the vicinity of the major thrust gave rise to the accommodation space for the aggradation of the recent fluvial sediments.
For a longitudinal distance of 212 km between the South Tibet Detachment (STD)and Himalayan Frontal Thrust (HFT), the valley has preserved significant aggradational landforms. These landforms have been physically examined to explain the spatial and temporal variability in phases of aggradation/incision in response to the tectonic activity during the late Quaternary. Fossil valleys and associated epigenetic gorges, cut-and-fill terraces with thick alluvial cover, debris-flow terraces, bedrock strath terraces, and alluvial fan terraces are the significant aggradational landforms observed within the valley. They provide signatures of tectonic activity and past climatic records. We have analysed various geomorphic indices, namely, stream-gradient index (SL), steepness index (Ks), hypsometric curve and index (HI), and asymmetric factor (AF) to map the spatial variability in tectonic processes across the major thrusts. The channel morphology (depth and width) of a river becomes adjusted in geological time because of long-term tectonic and erosional processes. However, the channel geometry and deviations can be highly adjustable in a tectonically disturbed mountainous region. The deviations along the river course can be attributed to active tectonic movement along thrusts/faults or because of erosion/sedimentation processes. We applied a novel method called the river Gradient Length Anomaly (GLA) for 37 subbasins of the Kali River to deduce active deformation (uplift/subsidence) corresponding to the increased sedimentation and erosional rates, both from the upstream and downstream parts of the thrusted blocks, from where river flows through. The results of basin-wise morphometric indices were corroborated with GLA anomaly and field observations, which suggests that the area has undergone active deformation between the Main Central Thrust (MCT) and Himalayan Frontal Thrust (HFT), which is attributed to the regional compression. The results of geomorphic and morphometric data are validated with the focal mechanisms of moderate earthquakes. The geomorphic analysis suggests that the hinterland part of eastern Kumaun is more active than the foreland region.
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