Glaciers and river systems

The Himalayan range encompasses about 15,000 glaciers, which store about 12,000 km3 of freshwater. The 70 km-long Siachen Glacier at the India-Pakistan border is the second longest glacier in the world outside the polar region. Some of the other more famous glaciers include the Gangotri and Yamunotri (Uttarakhand), Nubra, Biafo and Baltoro (Karakoram region), Zemu (Sikkim) and Khumbu glaciers (Mount Everest region).

The higher regions of the Himalayas are snowbound throughout the year, in spite of their proximity to the tropics, and they form the sources for several large perennial rivers, most of which combine into two large river systems:

* The western rivers combine into the Indus Basin, of which the Indus River is the largest. The Indus begins in Tibet at the confluence of Sengge and Gar rivers and flows southwest through India and then through Pakistan to the Arabian Sea. It is fed by the Jhelum, the Chenab, the Ravi, the Beas, and the Sutlej rivers, among others.

* Most of the other Himalayan rivers drain the Ganga-Brahmaputra Basin. Its two main rivers are the Ganga and the Brahmaputra and the Yamuna, among other tributaries. The Brahmaputra originates as the Yarlung Tsangpo River in western Tibet, and flows east through Tibet and west through the plains of Assam. The Ganga and the Brahmaputra meet in Bangladesh, and drain into the Bay of Bengal through the world's largest river delta.[2]

The eastern-most Himalayan rivers feed the Ayeyarwady River, which originates in eastern Tibet and flows south through Myanmar to drain into the Andaman Sea.

The Salween, Mekong, Yangtze and the Huang He (Yellow River) all originate from parts of the Tibetan plateau that are geologically distinct from the Himalaya mountains, and are therefore not considered true Himalayan rivers. Some geologists refer to all the rivers collectively as the circum-Himalayan rivers.[3] In recent years, scientists have monitored a notable increase in the rate of glacier retreat across the region as a result of global climate change.[4] Although the effect of this will not be known for many years, it potentially could mean disaster for the hundreds of millions of people who rely on the glaciers to feed the rivers of northern India during the dry seasons.[5]
Lakes
A high Himalayan lake at an altitude of around 5,000 metres Sikkim, India

The Himalaya region is dotted with hundreds of lakes. Most lakes are found at altitudes of less than 5,000 m, with the size of the lakes diminishing with altitude. The largest lake is the Pangong Tso, which is spread across the border between India and China. It is situated at an altitude of 4,600 m, and is 8 km wide and nearly 134 km long. A notable high (but not the highest) lake is the Gurudogmar in North Sikkim, at an altitude of 5,148 m (17,100 ft) (altitude source: SRTM). Other major lakes include the Tsongmo lake, near the Indo-China border in Sikkim, and Tilicho lake in Nepal in the Annapurna massif, a large lake in an area that was closed to tourists until recently.

The mountain lakes are known to geographers as tarns if they are caused by glacial activity. Tarns are found mostly in the upper reaches of the Himalaya, above 5,500 metres. For more information about these,

Origin and growth

The 6,000 km plus journey of the India landmass (Indian Plate) before its collision with Asia (Eurasian Plate) about 40 to 50 million years ago
Main article: Geology of the Himalaya

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 a fold 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 the Eurasian 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 by sedimentary 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 the Andaman 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.

Ecology

The flora and fauna of the Himalayas varies with climate, rainfall, altitude, and soils. The climate ranges from tropical at the base of the mountains to permanent ice and snow at the highest elevations. The amount of yearly rainfall increases from west to east along the front of the range. This diversity of climate, altitude, rainfall and soil conditions generates a variety of distinct plant and animal communities.Lowland forests

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.
The Terai belt

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).
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 forests occupy 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.
Shiwalik Hills

Also called Churia or Margalla Hills, Sivalik 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. 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.
Inner Terai or Dun Valleys

The Inner Terai valleys are open valleys north of Shiwalik Hills or nestled between Shiwalik subranges. Examples include Dehra Dun in India and Chitwan in Nepal.
Lesser Himalaya

Also called Mahabharat Range, the Lesser Himalayas is a prominent range 2,000 to 3,000 metres high formed along the Main Boundary Thrust fault zone, with a steep southern face and gentler northern slopes. Nearly continuous except for river gorges. Rivers gather in candelabra form to the north to break through this range in relatively few places.
Midlands

This 'hilly' region (Pahad), averaging about 1,000 metres immediately north of the Mahabharat Range, rises over about 100 km to about 4,000 metres at the Main Central Thrust fault zone, where the Greater Himalaya begin.

* Montane forests - At the middle elevations of the range, the subtropical forests yield to a belt of temperate broadleaf and mixed forests, with the Western Himalayan broadleaf forests at the western end of the range, and the Eastern Himalayan broadleaf forests in Assam and Arunachal Pradesh. Above the broadleaf forests are the Western and Eastern Himalayan subalpine conifer forests. The treeline is about 3,500 meters, so patchy alpine ecology is found in the highest parts of the midlands.

Greater Himalaya

North of the Main Central Thrust, the highest ranges rise abruptly as much as 4,000 meters 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 meters north of the Dhaulagiri Himalaya in central Nepal.

* Alpine shrub and grasslands - Above the tree line are the Northwestern, Western, and Eastern Himalayan alpine shrub and meadows, which yield to tundra in the higher Himalayan range. The alpine meadows are the summer habitat of the endangered snow leopard (Uncia uncia).

Trans-Himalaya

The watershed between rivers flowing south into the Ganges or Indus and rivers flowing north into the Brahmaputra or mainstem Indus that flow around the ends of the entire range often follows somewhat lower, less rugged mountains tens of kilometers north of the highest ranges. South-flowing rivers form valleys in this region, often semi-arid due to rainshadow effects. These valleys hold some of the highest permanent villages on earth.

about Himalaya

The Himalaya Range (Sanskrit: literally, "abode of snow", हिमालय, IPA pronunciation: [hɪ'mɑlijə]), or Himalayas 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).[1]

The Himalayan system, which includes outlying subranges, stretches across six countries: Afghanistan, Bhutan, People's Republic of China, India, Nepal, and Pakistan. Some of the world's major rivers, the Indus, the Ganges, the Brahmaputra, and the Yangtze, rise in the Himalayas, and their combined drainage basin is home to some 1.3 billion people, including the people of Bangladesh. The Himalayas have profoundly shaped the cultures of South Asia; many Himalayan peaks are sacred in both Hinduism and Buddhism.

The main Himalaya range runs, west to east, from the Indus river valley to the Brahmaputra river valley, forming an arc 2,400 km (1,491 mi) long, which varies in width from 400 km (249 mi) in the western Kashmir-Xinjiang region to 150 km (93 mi) in the eastern Tibet-Arunachal Pradesh region. The range consists of three coextensive sub-ranges, with the northern-most, and highest, known as the Great or Inner Himalayas.