GEOSPATIAL TECHNOLOGIES IN EVALUATING MORPHOTECTONIC FEATURES IN SUB-HIMALAYAN REGION, INDIA

Abstract

The Himalaya is young mountain range with an extension of about 2400 kilometres from west to east having arc shape occurs along the northern edge of Indian sub-continent. It is the classic example of collision-type orogenic belt and it consists mostly of uplifted sedimentary and metamorphic rocks (Gansser, 1964; Dhital, 2015; Chakrabarti, 2016). The Himalaya was originated as a result of collision between the northward moving Indian continental mass with the Asian landmass. Due to continued moving and pushing of the Indian plate beneath the Eurasian plate several complex structures have developed in and around Himalayan region. Ongoing tectonic activity in the region is well indicated by moderate to large magnitude earthquakes, as well as prominent tectonically controlled geomorphic indicators. For this reason, it has attracted the attention of geoscientists for several decades. The northward movement of Indian plate resulted in crustal shortening in north which is accommodated by south-verging thrusts (Thakur, 2004). The major longitudinal tectonic features present are Indus-Tsangpo Suture Zone (ITSZ), Main Central Thrust (MCT), Main Boundary Thrust (MBT), and Himalayan Frontal Thrust (HFT). These thrusts show relatively young age and shallowing depth, suggesting that the main deformation front has shifted southward (Thakur, 2004). In the western Himalaya, large numbers of recesses are present in the deformation front. These recesses are described as re-entrants (Thakur and Rawat, 1992). Kangra re-entrant is the largest of these recesses. Karunakaran and Ranga Rao (1979) have attributed the formation of these re-entrants to the effect of basement wedges in the underlying Indian Plate. Himalayan belt is most seismo-tectonically active and youngest orogenic belt on the earth. Naturally occurring events such as earthquakes, cause sudden deformations inside the earth as well as on the surface. The HFT developing along the southernmost boundary of the Siwaliks belongs to the latest active region of the Himalaya. Some of the most destructive earthquakes have occurred historically in India took place within the Himalayan region. This research work is focused on the study of morphotectonic features based on morphometric indices, drainage anomaly etc. The study will also help in identifying occurrence of existing tectonic fault and terrain modification. As indicated by Gansser (1964) the Himalaya might be subdivided into five geological divisions from north to south in their longitudinal structure, by a progression of a parallel structural zones. The Sub-or Outer-Himalaya framing the foot-slope zone known as Siwaliks are delimited in the south by the Ganges alluvial plains, though the northern edge has an Abstract ii obviously illustrated structural component - the MBT. Between the MBT in the south and the MCT in the north lies the stretch of the Lesser Himalaya. Farther north, beyond MCT the zone is the Central Crystalline of Higher Himalaya. Present study area comprising Kangra re-entrant, Nahan salient and Dehradun re-entrant is located in Sub-Himalaya (actively deforming front of the Himalaya) and is bounded by HFT in south and MBT in north in Himachal Pradesh and Uttarakhand. It extends for about 350 km in length and average width of about 75 km. The Doon valley is bounded to the northeast by MBT that separates the Precambrian rocks of the Krol belt of the Lesser Himalaya to the Cenozoic sediments of the outer Himalaya (Thakur, 1992). The relief suddenly rises in the south in the form of Siwalik Hills (Mohand ridge) which is separated from the recent alluvial sediments by the Himalayan Frontal Thrust (HFT), commonly known as Mohand thrust. In the west the Mohand ridge is bounded by the Yamuna Fault and in the east, by the Ganga fault. The detailed and careful inspection of geomorphic features and geomorphic indices such as the Valley width, river sinuosity index, the river gradient index, and drainage pattern can help in the understanding of overall evolution of landform and its ongoing tectonic movement. Therefore, an integrated approach of Remote Sensing and Geographic Information Systems (GIS) is used in the present study. The north-western edge of Kangra re-entrant in the NW Himalaya witness of 1905 great Kangra earthquake.. It is bounded by Himalayan Frontal Thrust (HFT) in south and Main Boundary Thrust (MBT) in north in Himachal Pradesh. Ongoing tectonic activity in the region is well indicated by moderate to large magnitude earthquakes, as well as prominent tectonically controlled geomorphic indicators. Identification of morphotectonic features, analysis of drainage network and finding out its relation to tectonics are the main objective of the present study. It has been observed that due to the Kangra re-entrant structure, large number of landforms has developed which are marked by NW-SE trending linear ridges. Extensive river network also have formed in the area and rivers have crossed the ridges at several places. The longitudinal profile of the Beas River clearly shows the HFT, Jwalamukhi thrust and MBT. Among these, Jwalamukhi thrust and MBT are very prominent. River becomes braided within the Kangra valley after entering Jaisingpur and near Jwalamukhi thrust. The sinuosity of the river increases and deep valley can be seen formed before the thrust. Hypsometric curve and hypsometric integral are used for watershed health indicator. In a tectonically active region, the basin topography is generally dynamic and its evolution responds Abstract iii to the stress regime of the region. The basin topography is also highly affected by the extent of erosional activities ongoing in the region. In Himalayan system, which is a highly active orogeny, the fluvial erosion plays a significant role in modifying the morphology. The quantification of this interplay of the tectonic uplift and subsequent erosion can be done in the form of a geomorphic index (Weissel et al., 1994). Based on the very same understanding of this interaction, several researchers have carried out hypsometric analysis to study the tectono-geomorphic evolution of different regions (Pandey et al., 2004; Singh et al., 2008a; Singh et al., 2008b; Sharma and Seth 2010 and Sharma et al., 2011). The basins can be classified by analysing the shape of hypsometric curves. These curves may be convex upward, S-shaped (concave upwards at high elevations and convex downwards at low elevations) or concave upward implying the youth, mature and peneplain stage of the basin, respectively (Strahler, 1952). The hypsometric integral value has applications for soil and water conservation measures also as it can be used to assess the erosion status of watershed (Singh et al. 2008). The present work involves study of role of active tectonics in channel modification and watershed geometry over Mohand anticline using morphometric tools. Hypsometric analysis of the study area also shows significant changes in sub-basins of all major rivers comes under study area that are Beas, Sutlej, Yamuna and Ganga. Hypsometric analysis of watershed demonstrates the complexity of denudation processes and the rate of morphological changes. Therefore, it is useful to comprehend the erosion status of watersheds and prioritize them for undertaking soil and water conservation measures. With the hypsometric integral and hypsometric profile, we can identify and predict the geological stages of all watersheds. According to the hypsometric curves of watersheds, it is observed that Khajnaur Rao and Mohan Rao watersheds are having more influence of tectonic activity. According to hypsometric integral values of the entire watersheds lie on the Mohand Anticline showing different geological stages. Hypsometric integral (HI) of Khajnaur Rao and Mohand Rao watersheds are having values 0.41 and 0.44 respectively. This also indicates that Mohand Rao and Khajnaur Rao watershed are more prone to erosion in comparison to other watersheds adjacent to it. The most important confirmation for fault identification has been given by the dislocation and displacement of mountain ridges and valleys, clearly recognizable lineaments, and drainage offsets observed in the true colour composite image of the area. Also, the morphometric Abstract iv analysis and shaded relief models (SRMs) created from DEM, further substantiates the presence of such features in the study area. Significant and unique tectonic feature depicting re-entrant and salient have formed comprising both the curved and northwest-southeast trending linear ridges. The folded rocks forming linear ridges are the result of fault propagation operated in these regions under the influence of prevailed convergent tectonics. The present topography exhibit effect of extensive erosion carving out several erosional features in the area. These ridges also reveal effect of faulting through dislocations at many places. The nature of folded rocks in the re-entrant areas indicate the area were subjected to slow and low intensity deformation.