Together, the Himalayan mountain system is the planet's highest and home to the world's highest peaks: the Eight-thousanders, including Mount Everest and K2. To comprehend the enormous scale of this mountain range consider that Aconcagua, in the Andes, at 6,962 m, is the highest peak outside Asia, while the Himalayan system includes over 100 mountains exceeding 7,200 meters.[2]
The Himalayan system, which includes outlying subranges, stretches across six countries: Bhutan, China, India, Nepal, Pakistan and Afghanistan. They are the source of three of the world's major river systems, the Indus, the Ganga-Brahmaputra, and the Yangtze. Approximately 1.3 billion people live in the drainage basin of the Himalayan rivers.
The range proper runs west to east, from the Indus river valley to the Brahmaputra river valley, thereby forming an arc 2,400 km long, which varies in width from 400 km in the western Kashmir-Xinjiang region to 150 km in the eastern Tibet-Arunachal Pradesh region. The Himalaya chain consists of three parallel ranges, with the northern-most range known as the Great or Inner Himalayas.
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, or extinct animals.
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 we
st 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 Siwalik 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 sal (Shorea robusta).
Siwalik Hills
Also called Churia or Margalla Hills. Intermittent outermost range of foothills extending across Himalayan region through Pakistan, India, Nepal and Bhutan. Consists of many sub-ranges. Summits generally 600 to 1,200 meters. Steeper southern slopes form along a fault zone called Main Frontal Thrust; 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
Open valleys north of Siwalik Hills or nestled between Siwalik subranges. Examples include Dehra Dun in India and Chitwan in Nepal.
Lesser Himalaya
Prominent range 2,000 to 3,000 meters high forming 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 place
Origins and growth
The Himalayas are among the youngest mountain ranges on the planet. 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 called 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/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/year, and over the next 10 million years it will travel about 1,500 km into Asia. About 20 mm/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/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.
Lakes
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 Tibet. 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 (16,890 ft) (altitude source: SRTM). Other major lakes include the Tsongmo lake, near the Indo-China border in Sikkim(India), and Tilicho lake in Nepal in the Annapurna massif, a large lake in an area that was closed to outsiders 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.
Impact on climate
The Himalayas have a profound effect on the climate of the Indian subcontinent and the Tibetan plateau. They prevent frigid, dry Arctic winds from blowing south into the subcontinent, which keeps South Asia much warmer than corresponding temperate regions in the other continents. It also forms a barrier for the monsoon winds, keeping them from traveling northwards, and causing heavy rainfall in the Terai region. The Himalayas are also believed to play an important part in the formation of Central Asian deserts such as the Taklamakan and Gobi deserts.
The mountain ranges also prevent western winter disturbances from Iran from traveling further, resulting in snow in Kashmir and rainfall for parts of Punjab and northern India. Despite being a barrier to the cold northernly winter winds, the Brahmaputra valley receives part of the frigid winds, thus lowering the temperature in the northeast Indian states and Bangladesh. These winds also cause the North East monsoon during this season for these parts.
In turn, the weather phenomenon called Jet Stream affects our image of the highest peaks on earth. The strong stream of winds from the west pass through Everest, creating a familiar plume of snows blowing from the summit, and visible from a great distance.
Mountain passes
The rugged terrain of the Himalaya makes few routes through the mountains possible. Some of these routes include:
* Gangtok in Sikkim to Lhasa in Tibet, via the Nathula Pass and Jelepla Passes (offshoots of the ancient Silk Road).
* Bhadgaon in Nepal to Nyalam in Tibet.
* Rohtang Pass in Himachal Pradesh, India.
* The road from Srinagar in Kashmir via Leh to Tibet. This pass is now less used because of regional troubles. Many people are affected.
* 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.
Himalaya
Himalaya is made up of two samskrit words - "Him" which means snow and "alaya" means house, together meaning the abode of snow
Him also means Nepalese "snow-covered mountain" and is used to name the various mountains of the Himalayas. In Nepal, these are as follows:
* Sagarmatha Himal
* Annapurna Himal
* Ganesh Himal
* Langtang Himal
* Manaslu Himal
* Rolwaling Himal
* Jugal Himal
* Gauri Sankar Himal
* Kanjirowa Himal
* Khumbu Himal
* Dhaulagiri Himal
