himalaya

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THE HIMALAYAN MOUNTAINS

INTRODUCTION : 

INTRODUCTION The Himalayas are among the youngest mountain ranges on the planet, and consist mostly of uplifted sedimentary and metamorphic rock. According to the modern theory of plate tectonics, their formation is a result of a continental collision or orogeny along the convergent boundary between the Indo-Australian Plate and the Eurasian Plate. This is referred to as afold mountain. The collision began in the Upper Cretaceous period about 70 million years ago, when the north-moving Indo-Australian Plate, moving at about 15 cm per year, collided with theEurasian Plate. About 50 million years ago, this fast moving Indo-Australian plate had completely closed the Tethys Ocean, the existence of which has been determined bysedimentary rocks settled on the ocean floor, and the volcanoes that fringed its edges. Since these sediments were light, they crumpled into mountain ranges rather than sinking to the floor. The Indo-Australian plate continues to be driven horizontally below the Tibetan plateau, which forces the plateau to move upwards. The Arakan Yoma highlands in Myanmar and theAndaman and Nicobar Islands in the Bay of Bengal were also formed as a result of this collision. The Indo-Australian plate is still moving at 67 mm per year, and over the next 10 million years it will travel about 1,500 km into Asia. About 20 mm per year of the India-Asia convergence is absorbed by thrusting along the Himalaya southern front. This leads to the Himalayas rising by about 5 mm per year, making them geologically active. The movement of the Indian plate into the Asian plate also makes this region seismically active, leading to earthquakes from time to time.

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The Himalaya Range or the Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau. By extension, it is also the name of a massive mountain system that includes the Karakoram, the Hindu Kush, and other, lesser, ranges that extend out from the Pamir Knot. Together, the Himalayan mountain system is the planet's highest, and home to the world's highest peaks, the Eight-thousanders, which include Mount Everest and K2. To comprehend the enormous scale of this mountain range, consider that Aconcagua, in the Andes, at 6,962 metres (22,841 ft) is the highest peak outside Asia, whereas the Himalayan system includes over 100 mountains exceeding 7,200 m (23,622 ft).

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On the Indo-Gangetic plain at the base of the mountains, an alluvial plain drained by the Indus and Ganga-Brahmaputra river systems, vegetation varies from west to east with rainfall. The xeric Northwestern thorn scrub forests occupy the plains of Pakistan and the Indian Punjab. Further east lie the Upper Gangetic plains moist deciduous forests of Uttarakhand and Uttar Pradesh and Lower Gangetic plains moist deciduous forests of Bihar and West Bengal. These are monsoon forests, with drought-deciduous trees that lose their leaves during the dry season. The moister Brahmaputra Valley semi-evergreen forests occupy the plains of Assam Lowland forests

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Above the alluvial plain lies the Terai strip, a seasonally marshy zone of sand and clay soils. The Terai has higher rainfall than the plains, and the downward-rushing rivers of the Himalaya slow down and spread out in the flatter Terai zone, depositing fertile silt during the monsoon season, and receding in the dry season. The Terai has a high water table due to groundwater percolating down from the adjacent zone. The central part of the Terai belt is occupied by the Terai-Duar savanna and grasslands, a mosaic of grasslands, savannas, deciduous and evergreen forests that includes some of the world's tallest grasslands. The grasslands of the Terai belt are home to the Indian rhinoceros (Rhinoceros unicornis). The Terai belt

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Bhabhar belt Above the Terai belt is an upland zone known as the Bhabhar, a zone of porous and rocky soils, made up of debris washed down from the higher ranges. The Bhabhar and the lower Shiwalik ranges have a subtropical climate. The Himalayan subtropical pine forestsoccupy the western end of the subtropical belt, with forests dominated by Chir Pine (Pinus roxburghii). The central part of the range is home to the Himalayan subtropical broadleaf forests, dominated by the sal tree (Shorea robusta). They are at the foot of the Himalayas where the Himalayan streams descend on to the plains.

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Shiwalik Hills Also called Churia or Margalla Hills, Shivalik Hills is an intermittent outermost range of foothills extending across the Himalayan region through Pakistan, India, Nepal and Bhutan. This region consists of many sub-ranges. Summits are generally 600 to 1,200 metres (2,000 to 3,900 ft). Steeper southern slopes form along a fault zone called Himalayan Frontal Thrust (HFT); northern slopes are gentler. Permeable conglomerates and other rocks allow rainwater to percolate downslope into the Bhabhar and Terai, supporting only scrubby forests upslope. The Himalayan subtropical pine and broadleaf forests continue here.

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Lesser Himalaya Also called Mahabharat Range, the Lesser Himalayas is a prominent range 2,000 to 3,000 metres (6,600 to 9,800 ft) high formed along the Main Boundary Thrust fault zone, with a steep southern face and gentler northern slopes. They are nearly continuous except for river gorges, where rivers from to the north gather like candelabra in a handful of places to break through the range. At these elevations and above the biogeography of the Himalayas is generally divided by the Kali Gandaki Gorge in central Nepal, one of the deepest canyons in the world. At the middle elevations of the range, the subtropical forests yield to a belt of temperate broadleaf and mixed forests growing between 1,500 and 3,000 metres (4,900 and 9,800 ft), with the western Himalayan broadleaf forests to the west of the Gandaki River, and the eastern Himalayan broadleaf forests to the east. The western broadleaf forests stretch from the Kashmir Valley, across Himachal Pradesh and Uttarakhand, and through western Nepal. The eastern broadleaf forests stretch across eastern Nepal, through Sikkim and Bhutan, and through much of Arunachal Pradesh.

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Midlands This 'hilly' region (Pahad), averaging about 1,000 metres (3,300 ft) immediately north of the Mahabharat Range, rises over about 100 kilometres (330,000 ft) to about 4,000 metres (13,000 ft) at the Main Central Thrust fault zone, where the Greater Himalaya begin. Above the broadleaf forests, between 3,000 and 4,000 metres (9,800 and 13,000 ft), are temperate coniferous forests, likewise split by the Gandaki River. The western Himalayan subalpine conifer forests are found below treeline in northern Pakistan, Jammu and Kashmir, Himachal Pradesh, Uttarakhand, and western Nepal. The eastern Himalayan subalpine conifer forests are found in eastern Nepal, Sikkim, Bhutan, and Arunachal Pradesh. Along the border between Arunachal Pradesh and Tibet, the eastern subalpine conifer forests mix with the northeastern Himalayan subalpine conifer forests. East Himalayan Fir, West Himalayan Spruce, and Himalayan Hemlock are some important trees of these forests. Rhododendrons are exceptionally diverse here, with over 60 species recorded in the northeastern Himalayan subalpine conifer forests.

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Greater Himalaya North of the Main Central Thrust, the highest ranges rise abruptly as much as 4,000 metres (13,000 ft) into the realm of perpetual snow and ice. As the Himalayan system becomes wider from east to west, the number of parallel high ranges increases. For example,Kagmara and Kanjiroba ranges both reach well over 6,000 metres (20,000 ft) north of the Dhaulagiri Himalaya in central Nepal. Montane grasslands and shrublands grow above treeline. The northwestern Himalayan alpine shrub and meadows are found in the high elevations of northern Pakistan, Jammu and Kashmir, and Himachal Pradesh. To the east, the western Himalayan alpine shrub and meadows cover extensive areas along the Tibetan border with Uttarakhand and western Nepal. The eastern Himalayan alpine shrub and meadows grow above the eastern and northeastern subalpine conifer forests, along the Tibetan border with eastern Nepal, Sikkim, Bhutan, and Arunachal Pradesh. The shrublands are composed of junipers as well as a wide variety of rhododendrons. They also possess a remarkable variety of wildflowers: Valley of Flowers National Park in the western Himalayan alpine shrub and meadows contains hundreds of species. The upper limit of the grasslands increases from west to east, rising from 3,500 metres (11,500 ft) to 5,500 metres (18,000 ft). The grasslands are the summer habitat of the endangered snow leopard (Uncia uncia).

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Mountain passes The rugged terrain makes few routes through the mountains possible. Some of these routes include: Banihal is an important pass connecting the hill areas of Jammu to the Kashmir Valley. Zoji La lies between the vale of Kashmir and the Kargil district, and is the only Western entrance to the highlands of Ladakh. Rohtang Pass in Himachal Pradesh, India. Mohan Pass is the principal pass in the Siwalik Hills, the southern most and geologically youngest foothills running parallel to the main Himalayas in Sikkim. Kora La at 4,594 metres (15,072 ft) elevation on the Nepal-Tibet border at the upper end of Mustang. The Kali Gandaki Gorge (agraben), transects the main Himalaya and Transhimalayan ranges. Kora La is the lowest pass through both ranges between K2 and Everest, but some 300 metres (980 ft) higher than Nathula and Jelepla passes further east between Sikkim and Tibet. Arniko Rajmarg/Friendship Highway route from Kathmandu, Nepal crossing into Tibet at Kodari/Zhangmu, to Nyalam, Lalung-La pass (5,050m/16,570'), Tingri, Xêgar, Lakpa La pass (5,250m/17,225'), to Lhatse on the Yarlung Tsangpo /Brahmaputra River about 460 road kilometers west of Lhasa. Gangtok in Sikkim to Lhasa in Tibet, via the Nathula Pass and Jelepla Passes (offshoots of the ancient Silk Road).

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Submitted by- Abhinav M S

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The End