Geomorphologic study of the valley floor in different tectonic segments along Kosi River valley between South Almora Thrust and Himalayan Frontal Thrust: Kumaun Himalaya, India

Abstract

In the Kumaun Himalaya, a portion of the Kosi River valley of ~90 km in length is chosen to study the fluvial morphology that provides first‐order information about the dynamic response of bedrock channels to tectonic impulse. The Kosi River flows across/along major tectonic boundaries such as the South Almora Thrust, Ramgarh Thrust, Main Boundary Thrust, and the Himalayan Frontal Thrust, and local transverse and longitudinal faults. Varied fluvial landforms correspond to different tectonic settings, lithologies, bedrock channels, hillslopes, large landslides, terraces, and fans. The longitudinal valleys are also the sites for thick aggradational landforms. Some portion of these valleys fall in the areas of active extensional tectonics and is characterized by one of the widest valley floor sections in the Lesser Himalaya. In contrast, the transverse valley sections are incised by deep‐cut v‐shaped valleys and the narrowest valley section. Swerving of the Kosi River is observed in the Ramgarh Thrust and Amel Fault zones and also in the Main Boundary Thrust zone. Recent tectonic activity is evident from the presence of the faulted Quaternary deposits, linear fault scarps, abandoned channels, incised meandering, and multiple levels of terraces/strath terraces. Field observations and the computed ratio of valley floor width to valley height (Vf) corroborate each other. Valleys developed parallel to the strike of faults and bedrocks have relatively broader valleys with higher Vf values whereas in contrast, the valleys developed across the bedrock strike are narrow with smaller Vf values. The results of computed stream length gradient (SL) and steepness (Ks) indices show considerable correlations between the obtained SL and Ks data and the field evidences; high values of SL and Ks are characterized by the presence of knick points observed at the prominent thrusts and faults.

Late Quaternary deformation in parts of the Belt of Schuppen of Dimapur and Peren districts, Nagaland, NE India

“…A change in the trend of the mountain front has resulted in the formation of a local syntaxial bend. A similar localized syntaxial bend along the mountain front is reported from the Tanakpur area of the Kumaun Himalaya, which was formed because of indentation of the Moradabad Fault into the Himalaya (Luirei et al, ; Raiverman, ; Valdiya, ). The curve in the mountain front in the present study area may be because of the subsurface extension of the Karbi Anglong (formerly Mikir) Hills, indenting into the frontal part of the Naga Hills in the form of a subsurface ridge.…”

“…Surface evidences include offset streams, diverted streams, strath terraces, faulted terraces, warped terraces, and tilted terraces (Keller & Pinter, ; Pérez‐Peña, Azor, Azañón, & Keller, ; Sieh & Jahns, ). In the Himalayas, diversions of major rivers and streams are directly related to neotectonics; swerving of rivers is observed in the major thrust zones and growing anticlines (Gupta, ; Luirei , Bhakuni, & Kothyari, ; Singh & Tandon, ). To supplement field evidences, morphometric analyses have been carried out in various tectonic terrains of the world.…”

Spatial interrelationship of landslides, litho‐tectonics, and climate regime, Satluj valley, Northwest Himalaya

“…Considering the mapping limitations of the GE Imagery, ground truthing has also been practiced to undermine these limitations by comparing known distances on the ground with GE measurement (Cascini et al, ; Mohammed, Ghazi, & Mustafa, ). To infer spatially varying tectonic regime, steepness index (k s ) of stream power erosion law (Flint, ) and valley floor width to valley height ratio (V f ), proposed by Bull and McFadden () have been used as common proxies in different studies (Howard & Kerby, ; Luirei, Bhakuni, & Kothyari, ; Wobus et al, ). Topographic swath profile is another such proxy that has been found useful in revealing tectonic influences on the topography (Telbisz, Kovács, Székely, & Szabó, ).…”

Quaternary landform study in Kosi and Dabka river valleys in Kumaun sub‐Himalaya: Implication of reactivation of thrusts

“…All the terraces of the Syat–Patliya section are predominantly made up of clasts of the Mussoorie Group. In the adjoining Kosi River valley, the MBT zone is defined by the development of broad terraces that measure about 1.5 km in width; a sudden narrowing down of valley is observed in the footwall block of the MBT (Luirei, Bhakuni, & Kothyari, ). Further downstream at Garjiya, the Kosi River valley narrows down from 1.2 km to about 122 m in the footwall block of the Sarpduli–Dhikala Thrust zone.…”

“…Morphotectonic evidences of the neotectonic activity along the HFT are reported from various segments of the Himalaya, from the classical works of Nakata () including palaeoseismic (Valdiya, ; Yeats et al, ; Valdiya, ; Wesnousky, Kumar, Mohindra, & Thakur, ; Lavé & Avouac, , ; Lavé et al, ; Malik & Nakata, ; Thakur, ; Goswami & Pant, , ; Agarwal, Bali, & Singh, ; Luirei & Bhakuni, ; Singh & Tandon, ; Parkash, Rathor, Pati, Jakhmola, & Singh, ; Agarwal & Sharma, ; Agarwal, Prakash, Nawaz Ali, & Jahan, ; Philip, Bhakuni, & Suresh, ; Mukul & Singh, ; Luirei, Bhakuni, & Kothyari, ). Tectonic‐induced stream migrations in the frontal part of the mountain front have been dealt with in detail by Malik et al () and Luirei, Bhakuni and Kothyari ().…”