Morphotectonic Analysis of the Himalayan Frontal Region of Northwest Himalaya in the Light of Geomorphic Signatures of Active Tectonics

Abstract

Among the principal thrust belts in the Himalaya such as Main Central Thrust (MCT), Main Boundary Thrust (MBT), and Himalayan Frontal Thrust (HFT), the HFT represents a zone of active deformation between the sub-Himalaya and Indo-Gangetic alluvial plain. The active deformation along the HFT causes tectonic tilting of the terrain and development of different types of tectonic landforms, subtle topographic breaks, and drainage anomalies. The landform development process in the Himalaya is a result of mutual interaction between climate and tectonics (Molnar 2003; Starkel 2003; Srivastava and Misra 2008; Kothyari et al. 2010). In fact, simultaneously operating tectonic and physical processes results in the present-day topography of the terrain (England and Molnar 1990; Bishop 2007). Various tectonic landforms such as fault scarps, stream terraces, back-tilted terraces, relict geomorphic surfaces, alluvial fan offsets, topographic breaks in piedmont-alluvial plain, drainage anomalies, and drainage diversions were observed in and around the HFT (Nakata 1972; Ruhe 1975; Thakur and Pandey 2004; Singh and Tandon 2008; Tandon and Singh 2014). A few-meter-high NW-SE trending scarp of discontinuous nature is observed in the piedmont-alluvial region in front of the HFT at several localities between Pinjore Dun and Dehra Dun (Thakur 2004). Besides, a number of archaeological evidences in the foothill regions of Uttarakhand (Piran Kaliyar in Roorkee district), Uttar Pradesh (Khajnawar and Bargaon in Saharanpur district), and Haryana (Bhirrana and Balu in Fatehabad district) raise the possibility of active tectonic events to cause such extinction and burial. Several factors such as topography, rock types, geological structures, soil, and vegetation cover essentially govern the development of a drainage system including channel morphology and drainage pattern. Primarily, active tectonics manifest itself by either steepening or reducing the local valley gradient which in turn changes the existing slope of the channels and introduces disturbance in the natural equilibrium of a drainage system. In the process of restoring the equilibrium, the river tries to adjust to the new conditions by changing its slope, cross-sectional shape, and meandering pattern (Vijith and Satheesh 2006; Pérez-Peña et al. 2010). In general, the phenomena like river incision, asymmetry of the catchment, and river diversion are accelerated by the tectonic processes (e.g., Cox 1994; Jackson et al. 1998; Clark et al. 2004; Salvany 2004; Schoenbohm et al. 2004). Several geomorphic parameters and indices describing tectonic tilting of the catchment, changes in the geometry and slope of the longitudinal and cross profiles of the rivers, anomalous hypsometric curve with high hypsometric integral value, anomalously low (< 1.0) valley floor width to valley ratio, and anomalous mountain front sinuosity index (close to 1.0) can be used to evaluate present-day tectonic activity on drainage basin scale (Bull and McFadden 1977; Rockwell et al. 1985; Keller and Gurrola 2000; Azor et al. 2002; Silva et al. 2003; Molin et al. 2004; Bull 2007; Malik and Mohanty 2007; Ata 2008; Pérez-Peña et al. 2010; Giaconia et al. 2012; Mahmood and Gloaguen 2012).