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Himalaya is one of the highest mountain range in the world evolved through the subduction of Indian plate under the Eurasian plate. The Himalayan chain extend from Europe through Iran, Afghanistan, Pakistan, India, Nepal and Burma, to Indonesian arc system starting from Nanga-Parbat (8125m) in the west to the Namcha Barwa (7828m) in the east. The 325-425 Km broad Himalayan range extends for a length of about 2500 Km. It forms two sharp hair-pin bends at its northwestern and northeastern limits referred to as “ Syntaxial- bends” (Wadia, 1931).
The Himalayan range is embraced at its western and eastern extremities by the Indus and Brahmputra rivers respectively. The arc-shaped mountain is convex southwards towards the Indian shield and embodies big bulges and inward pointing acute angles called the re-enterants of the mountain ranges (Valdiya, 1998).
The Indian plate collision to Eurasian plates and northwest ward movement created the Himalayan mountain arc system which stretch 2,500 km (1,500 mi), between 75°E and 98°E, from Kashmir in the West to Arunachal in the East.
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In the primary phase Tethys Sea situated at southern part of Eurasia plate, which separated of the two continents. The collision of Indian plate with Eurasian plate produced the world highest topographic landscape on globe. The Himalaya orogeny characterize one of the major tectonic zones in earth, where a continental crust under-thrust another continental crust.
The movement of Indian land mass toward northwest direction causes the underneath sedimentary masses with its solid basement under multiple deformation and divided by faulting, folding and thrusting.
(Kayal, 2014). The deformation contact zone from northern to southern is the Indus Suture Thrust (IST), the Main boundary Thrust (MBT), The Main Central Thrust (MCT) and the Himalayan Frontal Thrust (HFT). The IST represents the junction of two continents collision region. Main central thrust (MCT) is the fault system that develops along the south part of Higher Himalaya and separated the higher Himalaya between lesser Himalayas. Likewise, Main Boundary thrust (MBT) is north dipping series of thrust fault situated on the south part of the lesser Himalaya and separated the sub-Himalayan rocks. The Himalayan frontal thrust identify the north dipping thrust fault system which separated the Himalayan orogeny to Indian plate.
The Himalayan orogeny classified based on the criterion of geography, stratigraphy, structure, and political. Observation of Ganesser, Wadia, Lefort, the Himalayan region categorized into four geological Unit. These units are supposed to continuous along the whole Himalayan structures.
The Sub-Himalaya region composed of mainly Himalayan river deposit and diastrophism. The Siwalik Hills are the product of folding, faulting and upliftment of sub-Himalaya rocks. Along the MBT, Lesser Himalayas rocks have been under-thrust by sub-Himalaya. In the sub- Himalaya area the process of diastrophism begun during Pliocene time and has been presented as dynamic through the Pleistocene. The Himalayan frontal thrust (HFT) is south boundary of the Sub-Himalaya rocks. Lesser Himalaya region is restricted by Main Boundary Thrust (MBT) and Main Central Thrust in south and North respectively. In lesser Himalaya major rock units is green-schist metamorphism rocks, and sedimentary rock varieties from Indian plates.
Sequence of anticlines and synclines are presented in lesser Himalayan region. The Central Crystalline Zone, contained of ductile distorted metamorphic rocks and marks the axis of orogenic uplift is recognized as Higher Himalayan zone. The main rock variety in topmost higher Himalayan zone is Mica schist, quartzite, parageneiss, migmatites and leucogranite. These rocks represents a multiphase distortion results, the initial existence Barrovian type, or ordinary geothermal gradient situation. Main central thrust (MCT) is connected north to south direction along deformation zone, which conveys the Higher Himalaya on top of the Lower Himalayas.
The boundary between Eurasia and Indian plate or northern boundary of Himalaya marked as Indus-Tsangpo Suture Zone (ITZS). Main rock criterion of theses zone are ophiolites and ophiolitic complexes. The Himalayan progression has been largely separated into two phases (a) The Eo-Himalayan event that happened during the middle Eocene to Oligocene (45-25 Ma) and the, (b) The Neo- Himalayan event that occurred the early Miocene. Stratigraphically, the Himalayan Orogeny consists of the Neogene Siwalik Group, the Lower Himalayan Sequence (LHS), and the Proterozoic-Ordovician Greater Himalayan Crystalline Complex (GHC) and the Proterozoic to Eocene Tethyan Himalayan Sequence (THS). The major Tectonic-stratigraphic units in the Himalayan orogeny are separate as the Main Frontal Thrust hanging wall, Main Boundary Thrust hanging wall, Main Central Thrust hanging wall, and South Tibetan detachment hanging wall. Figure 2 Major Division of Himalaya (Picture taken From IITK repository)
Geomorphology of Himalaya are controlled by surface upliftment, Plate tectonics setting, climate variation and exhumation processes. Himalayan region have great diversity in height variation in south to north followed by Himalayan foot hill region 640 m. to greater Himalaya 8,850 m. from MSL, the change in altitude and climate factor effected in regional Himalayan geomorphology. Plate tectonic setting; The continent collision between Eurasia and India produce world highest mountain, collision begun about 50 Myr ago but present movement of Indian plate beneath Eurasian plate cause upliftment of young mountain. Precipitation; the monsoon effect in Himalaya is the major factor of mass wasting.
Slope instability, drainage density, fluvial action, effect the regional landscape in Himalayan region. In sub Himalayan region where mountain building movement are high reflected in fluvial geomorphological surface where River Terraces, old alluvial remanent reproduces the break of the continuous production of fluvial surface. The sequence of depositional and erosional process of fluvial agent controlled by tectonics uplift movement and monsoonal variation in Himalayan foot hill region. (Nakata, 1972). The rivers of foot hill zone are clearly indicate the active tectonics zone by drainage deflection, along the fault/thrust line, uplifted block of old alluvial remanent.
The progression of Himalayan foot hill landforms is orderly by slow tectonic change and river geomorphology, multi cyclic geomorphic surface gives the surface indicator of break in old alluvial plain. The Himalayan Frontal Thrust divides the Sub-Himalayas from the Lower Himalayas. Width of lower Himalaya is 60 to 70 km and altitude of lower Himalaya is 2,000 to 3,300 m (Nakata, 1972). These ranges contain of unfossiliferous Palaeozoic and Mesozoic formations of extremely tectonic deformed formation. South margin of lesser Himalayas are thrust over the sub-Himalaya along the HFT. Sub-Himalayas average altitude is 1,300 m in elevation and width is 10 to 90 km, dominated by Siwalik formation the Molasses of the Himalayas.
The distortedly folded bedding plane primarily dipping in direction of north indicate the Siwaliks zone, dissimilar structure pattern and alignment of deposited feature make difference with sub-Himalayas. The HFT and surrounding area are primary place of deposition because of abrupt change in high relief to low relief area and geomorphic factors. The strong lineament indication presented in southern part of Himalaya shows that same origin as other margins boundary. The HFT region categorized on the basis of their geologic structure and geomorphological characteristics which indicate different type of lithological formation and crustal movements on different foothill region. HFT region is described by mainly three types of structures area, the piedmont are located in northern part of Indo- Gangetic Plain made by Khadar and Bāngar soils.
Dun is special type of longitudinal depression between Siwalik and lesser Himalayan region, somewhere dun area are not present along Siwalik because lesser Himalaya and Siwalik are merged with each other. And last one is Re-entrant types, which means a surface is made with two parallel ridges in low elevated area. Piedmont zone are dominantly presented in Eastern Himalayas, Dun are presented where Siwalik and lesser Himalaya separated by valley in Central Himalayas, the last one western Himalayas is cover by Re-entrant Type. (Nakata, 1972).
Morphotectonics branch of geomorphology concerned with the form and tectonic origins of large topographic features of the earth's surface (as continents, mountain ranges, river basins, etc.). Morphotectonics refers to the study of short- and long-term superficial evidences of tectonic activity. The surface expression of endogenous mechanism driving the tectonic activity is always represented by relative movements such as uplifting, subsidence and translation of the crust. The most sensitive parameter is the drainage and its relationship with structures which control the courses. The continuous processes of weathering and erosion leads to formation of landforms manifesting the control of tectonics. Multi-sensor and multi-date remotely sensed data and advanced digital image processing techniques are extremely useful to observe and map morphotectonic features.
In areas where rate of present day tectonism is considerable, several field indications can be directly observed. However, in other cases where rate of tectonism is mild or very slow, evidences mainly comes from morphotectonic investigations, which may demarcate the areas for detailed field investigations. The study of aerial photographs, satellite images topographic maps supported by ground truth survey reveals that the study area has a network of interlinked subsurface fractures. The features of neo-tectonic activities in the form of faults and lineaments has a definite control on the alignment of many rivers and their tributaries. Geology and Morphotectonics describes the regional geology and its correlation with major and minor geological structures. The study of slopes, aspects, drainage network represents the geology and helps in categorization of the land forms into different geomorphological classes representing the relationship of the geological structures.
Identification and Mapping of active fault on the premise of geographical, geomorphological and geophysical data, in the region of active tectonics several geomorphological indicator are presented like, atypical river terraces, controlled drainage, Knick points, pull-apart basins, sag ponds, shutter ridges, stream migration, sudden discontinuity of alluvial fans, triangular facets. With the development of satellite technology, remote sensing has been widely used to interpret the structures of active tectonic, fault zones and monitor ground deformations.
Geomorphological approach recognized the recently active breaks in terms of the related geomorphic features like channel offset, channel shift, linear ridge, linear valley, parallel ridges, sag pond, scarps, shutter ridge, spring, terrace and triangulated facet. The fault activity changes the geomorphic landform according to fault movement and fault geometry. The surface indicator of land form clearly marked on remote sensing satellite images/ aerial photo, the Digital elevation model is best explain the active tectonics area on remote sensing and GIS system. Morphotectonic investigation is fundamental tools in geomorphology to classify the relatively active region of area, Lineament study recognize the linear ridge, and parallel ridge and fault line on surface or under the subsurface. The special characteristic of geomorphic land surface are correlated with probable active fault area.
Drainage analysis is useful to identifying the active zone of the area, where plate movement, structure deformation and mass wasting is taking place. Drainage is surficial indicator of underneath geological and geotectonic setting. Drainage anomalies are the abnormalities from the probable drainage in a region. Certain drainage anomalies like deflected drainages, and compressed meanders reflect underlying faults with well-defined morphology. Interpretation of drainage anomalies and the related lineaments/faults provides information for neo-tectonic as well as active tectonic study in the area. Structural or morphotectonic control influences displacement; strike, dip (angles and directions) on landforms due to active tectonics. Sometimes surface expression of structural features is not clear hence includes the stratigraphy of the area; different structural pattern such as joints, faults, folds and bedding planes and lithology.
Drainage anomaly is part of regional drainage where drainage is controlled by climate, lithology or active tectonics. Drainage anomaly mainly shows the pattern of drainage in not follow the surrounding topographic rules. The drainage anomaly classified based on drainage special characteristic as Rectilinearity of drainage in homogenous medium, local or compress meandering, abrupt change is channel flow and change the river direction in opposite to topographic slope.
Drainage always follow the easiest path on a terrain until it connects with other streams in the drainage system. The behavior of drainage pattern influenced by different geologic structures underneath as well as terrain movement. Any abnormal deviation from the normal stream defines drainage distortion such as abrupt change in drainage direction, existence of compressed meanders and abrupt termination of drainage.
The Himalayan Mountain Range. (2021, Dec 17). Retrieved from https://studymoose.com/the-himalayan-mountain-range-essay
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