Tibetan Plateau

 

The Tibetan Plateau, also known as the Qinghai-Tibet Plateau or the Qing-Zang Plateau or as the Himalayan Plateau in India, is a vast elevated plateau located at the intersection of South, Central and East Asia covering most of the Tibet Autonomous Region,most of Qinghai, western half of Sichuan, Southern Gansu provinces in Western China, southern Xinjiang, Bhutan, the Indian regions of Ladakh and Lahaul and Spiti (Himachal Pradesh) as well as Gilgit-Baltistan in Pakistan, northwestern Nepal, eastern Tajikistan and southern Kyrgyzstan.

 

It stretches approximately 1,000 kilometres north to south and 2,500 kilometres east to west. It is the world's highest and largest plateau above sea level, with an area of 2,500,000 square kilometres (about five times the size of Metropolitan France). With an average elevation exceeding 4,500 metres and being surrounded by imposing mountain ranges that harbor the world's two highest summits, Mount Everest and K2, the Tibetan Plateau is often referred to as "the Roof of the World".

The Tibetan Plateau contains the headwaters of the drainage basins of most of the streams and rivers in surrounding regions. This includes the three longest rivers in Asia (the Yellow, Yangtze, and Mekong). Its tens of thousands of glaciers and other geographical and ecological features serve as a "water tower" storing water and maintaining flow. It is sometimes termed the Third Pole because its ice fields contain the largest reserve of fresh water outside the polar regions. The impact of climate change on the Tibetan Plateau is of ongoing scientific interest.

Description

The Tibetan Plateau is surrounded by the massive mountain ranges of high-mountain Asia. The plateau is bordered to the south by the inner Himalayan range, to the north by the Kunlun Mountains, which separate it from the Tarim Basin, and to the northeast by the Qilian Mountains, which separate the plateau from the Hexi Corridor and Gobi Desert. To the east and southeast the plateau gives way to the forested gorge and ridge geography of the mountainous headwaters of the Salween, Mekong, and Yangtze rivers in northwest Yunnan and western Sichuan (the Hengduan Mountains). In the west, the curve of the rugged Karakoram range of northern Kashmir embraces the plateau. The Indus River originates in the western Tibetan Plateau in the vicinity of Lake Manasarovar.

The Tibetan Plateau is bounded in the north by a broad escarpment where the altitude drops from around 5,000 metres (16,000 ft) to 1,500 metres over a horizontal distance of less than 150 kilometres. Along the escarpment is a range of mountains. In the west, the Kunlun Mountains separate the plateau from the Tarim Basin. About halfway across the Tarim the bounding range becomes the Altyn-Tagh and the Kunluns, by convention, continue somewhat to the south. In the 'V' formed by this split is the western part of the Qaidam Basin. The Altyn-Tagh ends near the Dangjin pass on the Dunhuang–Golmud road. To the west are short ranges called the Danghe, Yema, Shule, and Tulai Nanshans. The easternmost range is the Qilian Mountains. The line of mountains continues east of the plateau as the Qinling, which separates the Ordos Plateau from Sichuan. North of the mountains runs the Gansu or Hexi Corridor which was the main silk-road route from China proper to the West.

The plateau is a high-altitude arid steppe interspersed with mountain ranges and large brackish lakes. Annual precipitation ranges from 100 to 300 millimetres and falls mainly as hail. The southern and eastern edges of the steppe have grasslands that can sustainably support populations of nomadic herdsmen, although frost occurs for six months of the year. Permafrost occurs over extensive parts of the plateau. Proceeding to the north and northwest, the plateau becomes progressively higher, colder, and drier, until reaching the remote Changtang region in the northwestern part of the plateau. Here the average altitude exceeds 5,000 metres (16,000 ft) and winter temperatures can drop to −40 °C. As a result of this extremely inhospitable environment, the Changthang region (together with the adjoining Kekexili region) is the least populous region in Asia and the third least populous area in the world after Antarctica and northern Greenland.

Geology anh Geological History

The geological history of the Tibetan Plateau is closely related to that of the Himalayas. The Himalayas belong to the Alpine Orogeny and are therefore among the younger mountain ranges on the planet, consisting mostly of uplifted sedimentary and metamorphic rock. Their formation is a result of a continental collision or orogeny along the convergent boundary between the Indo-Australian Plate and the Eurasian Plate.

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. Palaeobotanical evidence indicates that Tibet remained a tropical or subtropical lowland until the latest Oligocene or Early Miocene. The Indo-Australian plate continues to be driven horizontally below the Tibetan Plateau, which forces the plateau to move upwards; the plateau is still rising at a rate of approximately 5 mm per year (although erosion reduces the actual increase in height).

Much of the Tibetan Plateau is of relatively low relief. The cause of this is debated among geologists. Some argue that the Tibetan Plateau is an uplifted peneplain formed at low altitude, while others argue that the low relief stems from erosion and infill of topographic depressions that occurred at already high elevations.

The current tectonics of the plateau is much debated. The two end-member models are the block model, in which the crust of the plateau is formed of several blocks with little internal deformation separated by major strike-slip faults. In the alternative continuum model, the plateau is affected by distributed deformation resulting from flow within the crust.

Environment

The Tibetan Plateau supports a variety of ecosystems, most of them classified as montane grasslands. While parts of the plateau feature an alpine tundra-like environment, other areas feature monsoon-influenced shrublands and forests. Species diversity is generally reduced on the plateau due to the elevation and low precipitation. The Tibetan Plateau hosts the Tibetan wolf, and species of snow leopard, wild yak, wild donkey, cranes, vultures, hawks, geese, snakes, and water buffalo. One notable animal is the high-altitude jumping spider, that can live at elevations of over 6,500 metres.