Himalayas
The Himalayas, or Himalaya, is a mountain range in Asia separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the Earth's highest peaks, including the highest, Mount Everest. More than 100 peaks exceeding elevations of above sea level lie in the Himalayas.
The Himalayas abut on or cross territories of five countries: Nepal, India, China, Bhutan and Pakistan. The sovereignty of the range in the Kashmir region is disputed among India, Pakistan, and China. The Himalayan range is bordered on the northwest by the Karakoram and Hindu Kush ranges, on the north by the Tibetan Plateau, and on the south by the Indo-Gangetic Plain. Some of the world's major rivers, the Indus, the Ganges, and the Tsangpo–Brahmaputra, rise in the vicinity of the Himalayas, and their combined drainage basin is home to some 600 million people; 53 million people live in the Himalayas. The Himalayas have profoundly shaped the cultures of South Asia and Tibet. Many Himalayan peaks are sacred in Hinduism and Buddhism. The summits of several—Kangchenjunga, Gangkhar Puensum, Machapuchare, Nanda Devi, and Kailash in the Tibetan Transhimalaya—are off-limits to climbers.
The Himalayas were uplifted after the collision of the Indian tectonic plate with the Eurasian plate, specifically, by the folding, or nappe-formation of the uppermost Indian crust, even as a lower layer continued to push on into Tibet and add thickness to its plateau; the still lower crust, along with the mantle, however, subducted under Eurasia. The Himalayan mountain range runs west-northwest to east-southeast in an arc long. Its western anchor, Nanga Parbat, lies just south of the northernmost bend of the Indus river. Its eastern anchor, Namcha Barwa, lies immediately west of the great bend of the Yarlung Tsangpo River. The Indus-Yarlung suture zone, along which the headwaters of these two rivers flow, separates the Himalayas from the Tibetan plateau; the rivers also separate the Himalayas from the Karakorams, the Hindu Kush, and the Transhimalaya. The range varies in width from in the west to in the east.
Etymology
The name of the range hails from the Sanskrit Himālaya, from hima and ālaya. The cognates include:- हिमालय Himālaya in Nepali and Hindi,
- हिंवाळ Hinvāl in Garhwali,
- हिमाल Himāl in Kumaoni,
- ཧི་མ་ལ་ཡ་ Himalaya in Tibetan,
- හිමාලය Himālaya in Sinhala,
- Himāliya in Urdu,
- হিমালয় Himaloẏ in Bengali,
- 喜马拉雅 or 喜馬拉雅 Xǐmǎlāyǎ in Chinese.
The name of the range is sometimes also given as Himavan in older writings, including the Sanskrit epic Mahabharata. Himavat '' or Himavan Himavān is a Hindu deity who is the personification of the Himalayan Mountain Range. Other epithets include Himaraja 'The Land of Snow' in Tibetan, or Parvateshwara.
Geography and key features
The Himalayas consists of four parallel mountain ranges from south to north: the Sivalik Hills on the south; the Lower Himalayan Range; the Great Himalayas, which is the highest and central range; and the Tibetan Himalayas on the north. The Karakoram are generally considered separate from the Himalayas.In the middle of the great curve of the Himalayan mountains lie the peaks of Dhaulagiri and Annapurna in Nepal, separated by the Kali Gandaki Gorge. The gorge splits the Himalayas into Western and Eastern sections, both ecologically and orographically – the pass at the head of the Kali Gandaki, the Kora La, is the lowest point on the ridgeline between Everest and K2. To the east of Annapurna are the peaks of Manaslu and across the border in Tibet, Shishapangma. To the south of these lies Kathmandu, the capital of Nepal and the largest city in the Himalayas. East of the Kathmandu Valley lies the valley of the Bhote/Sun Kosi river which rises in Tibet and provides the main overland route between Nepal and China – the Araniko Highway/China National Highway 318. Further east is the Mahalangur Himal with four of the world's six highest mountains, including the highest: Cho Oyu, Everest, Lhotse, and Makalu. The Khumbu region, popular for trekking, is found here on the south-western approaches to Everest. The Arun river drains the northern slopes of these mountains, before turning south and flowing to the range to the east of Makalu.
In the far east of Nepal, the Himalayas rise to the Kangchenjunga massif on the border with India, the third-highest mountain in the world, the most easterly summit and the highest point of India. The eastern side of Kangchenjunga is in the Indian state of Sikkim. Formerly an independent Kingdom, it lies on the main route from India to Lhasa, Tibet, which passes over the Nathu La pass into Tibet. East of Sikkim lies the ancient Buddhist Kingdom of Bhutan. The highest mountain in Bhutan is Gangkhar Puensum, which is also a strong candidate for the highest unclimbed mountain in the world. The Himalayas here are becoming increasingly rugged, with heavily forested steep valleys. The Himalayas continue, turning slightly northeast, through the Indian State of Arunachal Pradesh as well as Tibet, before reaching their easterly conclusion in the peak of Namche Barwa, situated in Tibet, inside the great bend of the Yarlang Tsangpo river. On the other side of the Tsangpo, to the east, are the Kangri Garpo mountains. The high mountains to the north of the Tsangpo, including Gyala Peri, however, are also sometimes included in the Himalayas.
Going west from Dhaulagiri, Western Nepal is somewhat remote and lacks major high mountains, but is home to Rara Lake, the largest lake in Nepal. The Karnali River rises in Tibet but cuts through the centre of the region. Further west, the border with India follows the Sarda River and provides a trade route into China, where on the Tibetan plateau lies the high peak of Gurla Mandhata. Just across Lake Manasarovar from this lies the sacred Mount Kailash in the Kailash Ranges, which stands close to the source of the four main rivers of Himalayas and is revered in Hinduism, Jainism, Buddhism, Sufism and Bonpo. In Uttarakhand, the Himalayas are regionally divided into the Kumaon and Garhwal Himalayas with the high peaks of Nanda Devi and Kamet. The state is also home to the important pilgrimage destinations of Chota Chaar Dhaam, with Gangotri, the source of the holy river Ganges, Yamunotri, the source of the river Yamuna, and the temples at Badrinath and Kedarnath.
The next Himalayan Indian state, Himachal Pradesh, is noted for its hill stations, particularly Shimla, the summer capital of the British Raj, and Dharamsala, the centre of the Tibetan community and government in exile in India. This area marks the start of the Punjab Himalaya and the Sutlej river, the most easterly of the five tributaries of the Indus, cuts through the range here. Further west, the Himalayas form much of the disputed Indian-administered union territory of Jammu and Kashmir where lie the mountainous Jammu region and the renowned Kashmir Valley with the town and lakes of Srinagar. The Himalayas form most of the south-west portion of the disputed Indian-administered union territory of Ladakh. The twin peaks of Nun Kun are the only mountains over in this part of the Himalayas. Finally, the Himalayas reach their western end in the dramatic 8000 m peak of Nanga Parbat, which rises over above the Indus valley and is the most westerly of the 8000 m summits. The western end terminates at a magnificent point near Nanga Parbat where the Himalayas intersect with the Karakoram and Hindu Kush ranges, in the disputed Pakistani-administered territory of Gilgit-Baltistan. Some portion of the Himalayas, such as the Kaghan Valley, Margalla Hills, and Galyat tract, extend into the Pakistani provinces of Khyber Pakhtunkhwa and Punjab.
Geology
, the recurring physical changes that affect the arrangement of the Earth's crust, and plate tectonics, the movement of large regions of the Earth's crust in the manner of planar rigid bodies, are key to understanding the formation of the Himalayas. The Earth's crust rests directly on its mantle. Tectonic plates, comprising the crust and the upper portions of their underlying mantle, are moved around by convection in the asthenosphere. The oceanic crust, found beneath oceans, is, on average, thick. It is created from upwelling magma at mid-ocean ridges and predominantly consists of basalt, the principal igneous rock on Earth. In contrast, the continental crust underlying dry land has an average thickness of and is rich in silica, which is less dense than basalt. It makes the continental tectonic plates more buoyant than the oceanic.India's defining geologic processes, which began 70 million years ago, had involved India rifting, or splitting away, from Gondwana, and the Indian continental plate along with the Neo-Tethys oceanic plate above it jointly moving northward. As these eventually reached the Eurasian plate, the less buoyant oceanic plate subducted, or slid under Eurasia and was carried into the deeper asthenosphere. In contrast, the Indian continental plate was obstructed because of its thickness and buoyancy. The lateral compression generated by the obstruction caused the plate to be sheared horizontally. Its lower crust and mantle slid under, but one layer of the upper crust piled up in sheets ahead of the subduction zone. Geophysicist Peter Molnar noted that most of the Himalayas are "slices of rock that once were the top part of India's crust." This is the process of mountain building, or orogeny, in the Himalayas.
Before the orogeny, the Eurasian coastline had been similar to today's Central Andes. Along such coastlines, the adjoining oceanic plate subducts and erupts as volcanoes. Magma, which eventually crystallizes into granite, rises into the Earth's crust below the active volcanoes but not to the surface. When India's continental plate pushed against Eurasia, not only did a part of the upper crust fold in nappes, but another stiffer part began to push against Eurasia's ancient volcanic mountains farther north. As a result, the crust of this formerly coastal region shortened under compression and thickened to become what is today the Tibetan Plateau. Isostatic equilibrium, or the balance between the gravitational force pulling down on the crust and the force of buoyancy pushing up from the mantle, gives the Tibetan Plateau its notable thickness and altitude.
The Indian plate was not the only landmass that had rifted from Gondwana and drifted northward toward Eurasia. Before the India-Eurasia collision in Middle Paleocene and subsequent Himalayan orogeny, two other landmasses, the Qiangtang terrane and Lhasa terrane, had drifted up from Gondwana. Qiangtang, a geological region in what is today northern Tibet, had done so in Late Triassic. The Lhasa terrane collided with the southern boundary of the Qiangtang in the Early Cretaceous. The collision caused the lithospheric mantle of the Lhasa terrane to thicken and shorten, forming a barrier that later prevented the Indian lithosphere from fully subducting under Tibet and leading to further thickening of the Tibetan plateau. The suture zones, or remains of the subduction zone and the terranes that are joined, are found in the Tibetan plateau. The Qiantang and Lhasa terranes were part of the string of microcontinents Cimmeria, today constituting parts of Turkey, Iran, Pakistan, China, Myanmar, Thailand and Malaysia, which had rifted from Gondwana earlier, closing the Paleo-Tethys Ocean above them and opening the Neo-Tethys Ocean between them and Gondwana, eventually colliding with Eurasia, and creating the Cimmerian Orogeny.
After the Lhasa terrane had adjoined Eurasia, an active continental margin opened along its southern flank, below which the Neo-Tethys oceanic plate had begun to subduct. Magmatic activity along this flank produced the Gangdese batholith in what is today the Tibetan trans-Himalaya. Another subduction zone opened to the west, in the ocean basin above the Kohistan-Ladakh island arc. This island arc—formed by one oceanic plate subducting beneath another, its magma rising and creating continental crust—drifted north, closed its ocean basin and collided with Eurasia.
The collision of India with Eurasia closed the Neo-Tethys Ocean. The suture zone, which marks India's welding to Eurasia, is called the Indus-Yarlung suture zone. It lies north of the Himalayas. The headwaters of the Indus River and the Yarlung Tsangpo flow along this suture zone. These two Eurasian rivers, whose courses were continually diverted by the rising Himalayas, define the western and eastern limits, respectively, of the Himalayan mountain range.
During the India-Eurasia collision, two elongated protrusions located on either side of the northern border of the Indian continent generated areas of extreme deformation. A point where mountain ranges with different directions of extension, and thus formed by tectonic forces at varying angles, converge is called a syntaxis. The two syntaxes, Nanga Parbat and Namche Barwa, on the northwestern and northeastern corners of the Indian continent, respectively, are characterized by the quick upward movement of land or rocks that were once deeply buried and significantly altered by extreme heat and pressure. Geologists have estimated the rate of uplift of these rocks to be per year, or per million years. The protruding regions have some of the highest mountain peaks at and, respectively. The regions also have the greatest topographical relief in the interior of a continent, approximately over a horizontal distance of. Nanga Parbat has a narrow, anticline, or arch-shaped fold whose crest dips sharply to the north, perpendicular to the general direction along which the Himalayas extend. The Indus and Yarlung Tsangpo, which originally emptied into the New-Tethys, now bend around the Nanga Parbat and Namche Barwa, respectively, to eventually empty into the Indian Ocean.
Geologists Wolfgang Frisch, Martin Meschede, and Ronand Blakey write, "India rapidly marched northward towards Asia with a velocity of ca. 20 cm/yr, a plate velocity that exceeds any modern example. This velocity considerably slowed to ca. 5 cm/yr following the collision, yet India continued to protrude into Asia for more than 2000 km.... The irregular northern margin of the Indian continental crust first came into contact with Eurasia along its northwestern corner, approximately 55 Ma. As a consequence, India underwent a counter-clockwise rotation to close the remaining part of the Neotethys in scissor-like fashion from west to east. The closure of the Neotethys was completed approximately 40 Ma."
Today, the Indian plate continues to be driven horizontally at the Tibetan Plateau, which forces the plateau to continue to move upwards. The Indian plate is moving at per year, and over the next 10 million years, it will travel into Asia. Approximately 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 annually, 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.
The Himalayan mountain range consists of three sub-ranges: the Higher- or "Tethys" Himalayas, the Lesser Himalayas, and the Siwaliks. The nappes—large, stacked sheets of rock—found in the Tethys Himalayan mountain range, are primarily composed of sedimentary rocks, such as limestone formed from the accumulation and compression of sediments like sand, mud, and shells deposited in the Neo-Tethys seabed during the Paleogene". Below the sedimentary rocks in the Higher and Lesser Himalayas is a bottom layer, or basement, composed of metamorphic rock formed much earlier during the Pan-African-Cadomian orogeny between 650 Mya and 550 Mya. The lowest subrange, the Siwaliks, represents the sedimentary rock deposits washed off the rising Himalayas in a foreland basin, a low-lying crustal region, at their foot. It primarily consists of sandstones, shales, and conglomerates formed during the Neogene period.
Geologists Wolfgang Frisch, Martin Meschede, and Ronand Blakey further write, "The Siwaliks are both underlain and overlain by thrusts; they have been overridden by the nappe stack of the Higher and Lesser Himalayas and, in turn, are thrust over more interior parts of the Indian continent. Each of the three mega-units is internally imbricated into several individual nappes. Fensters and klippen provide important structural information regarding the thrust belts and help document the existence of broad thrust sheets, some of which record thrust distances in excess of 100 km. A fenster or window is an erosional hole through a thrust sheet that exposes a tectonically lower unit framed by a higher unit; a klippe is detached by erosion and forms a remnant of a nappe or higher thrust sheet
that rests on top of a lower unit."