The Tibetan Plateau, also known in China as the Qinghai-Tibet Plateau or Himalayan Plateau,
is a vast elevated plateau in Central Asia or East Asia, covering most of the Tibet Autonomous
Region and Qinghai Province in western China, as well as part of Ladakh in Jammu and Kashmir
state of India. It stretches approximately 1,000 kilometres north to south and 2,500
kilometres east to west. With an average elevation exceeding 4,500 metres, the Tibetan Plateau
is sometimes called "the Roof of the World" and is the world's highest and largest plateau,
with an area of 2,500,000 square kilometres. Sometimes termed the "Third Pole", the Tibetan
Plateau is the headwaters of the drainage basins of most of the streams in surrounding
regions. Its tens of thousands of glaciers and other geographical and ecological features
serve as a "water tower" storing water and maintaining flow. The impact of global warming
on the Tibetan Plateau is of intense scientific interest.
Description The Tibetan Plateau is surrounded by massive
mountain ranges. The plateau is bordered to the south by the Himalayan range, to the north
by the Kunlun Range which separates it from the Tarim Basin, and to the northeast by the
Qilian Range which separates 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 western Sichuan
and southwest Qinghai. In the west the curve of the rugged Karakoram range of northern
Kashmir embraces it.
The Tibetan Plateau is bounded on the north by a broad escarpment where the altitude drops
from around 5,000 metres to 1,500 metres in 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 half way 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 Qin Mountains which separate the Ordos Region 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 hailstorms. The southern and eastern edges
of the steppe have grasslands which 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 Changthang region in the northwestern part of the plateau.
Here the average altitude exceeds 5,000 metres and winter temperatures can drop to −40 °C.
As a result of this extremely inhospitable environment, the Changthang region is the
least populous region in Asia, and the third least populous area in the world after Antarctica
and northern Greenland.
Geology and geological history
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.
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 plateau is still rising about 5 mm per year.
Animal and plant life
Tibet's elevation and lack of precipitation produces an alpine tundra environment, which
reduces species diversity. Tibet hosts species of wolf, wild donkey, cranes, vultures, hawks,
geese, snakes, and buffalo. One notable animal is the high-altitude jumping spider, that
can live at over 6,500 metres of elevation. Nomadic culture
Nomads on the Tibetan Plateau and in the Himalayas are the remainders of nomadic practices historically
once widespread in Asia and Africa. Pastoral nomads constitute about 40% of ethnic Tibetan
population. Their presence was made possible by the adaptation of nomadic people to survive
on the world's grassland by raising livestock rather than crops which are unsuitable to
the terrain. Archaeological evidence suggests that the colonization leading to the full-time
occupation of the plateau occurred much later than the previously thought 30,000 years ago.
Impact on other regions Role in monsoons
Monsoons are caused by the larger amplitude of the seasonal cycle of land temperature
compared to that of nearby oceans. This differential warming happens because heat in the ocean
is mixed vertically through a "mixed layer" that may be fifty meters deep, through the
action of wind and buoyancy-generated turbulence, whereas the land surface conducts heat slowly,
with the seasonal signal penetrating perhaps a meter or so. Additionally, the specific
heat capacity of liquid water is significantly higher than that of most materials that make
up land. Together, these factors mean that the heat capacity of the layer participating
in the seasonal cycle is much larger over the oceans than over land, with the consequence
that the air over the land warms faster and reaches a higher temperature than the air
over the ocean. The hot air over the land tends to rise, creating an area of low pressure.
This creates a steady wind blowing toward the land, bringing the moist near-surface
air over the oceans with it. Similar rainfall is caused by the moist ocean air being lifted
upwards by mountains, surface heating, convergence at the surface, divergence aloft, or from
storm-produced outflows at the surface. However the lifting occurs, the air cools due expansion
in lower pressure, which in turn produces condensation.
In winter, the land cools off quickly, but the ocean keeps the heat longer. The hot air
over the ocean rises, creating a low pressure area and a breeze from land to ocean while
a large area of drying high pressure is formed over the land, increased by wintertime cooling.
Monsoons are similar to sea and land breezes, a term usually referring to the localized,
diurnal cycle of circulation near coastlines everywhere, but they are much larger in scale,
stronger and seasonal. The seasonal monsoon wind shift and weather associated with the
heating and cooling of the Tibetan plateau is the strongest such monsoon on Earth.
Glaciology: the Ice Age and at present
Today, Tibet is an important heating surface of the atmosphere. However, during the Last
Ice Age a c. 2,400,000 square kilometres ice sheet covered the plateau. Due to its great
extent, this glaciation in the subtropics was an important element of radiative forcing.
With a much lower latitude, the ice in Tibet reflected at least 4 times more radiation
energy per unit area into space than ice at higher latitudes. Thus, what at present adds
heat to the atmosphere subtracted it instead. This cooling had multiple effects on regional
climate. Without the thermal low caused by the heating, there was no monsoon over the
Indian subcontinent. This lack of monsoon caused extensive rainfall over the Sahara
desert, expansion of the Thar desert, more dust deposited into the Arabian Sea, and a
lowering of the biotic life zones on the Indian subcontinent. Animals responded to this shift
in climate, with the Javan Rusa deer migrating into India.
In addition, the glaciers in Tibet created meltwater lakes in the Qaidam Basin, the Tarim
Basin and the Gobi Desert, despite the strong evaporation caused by the low latitude. Silt
and clay from the glaciers accumulated in these lakes: when the lakes dried at the end
of the ice age, the silt and clay were blown by the downslope wind off the Plateau. These
airborne fine grains produced the enormous amount of loess in the Chinese lowlands.
Since the end of the ice age, Tibet has risen at approximately 10 millimetres per year,
at the same rate as the Himalaya. While the Himalaya rise can be explained by plate tectonics,
the rise of Tibet can be explained as the isostatic rebound of the crust rising after
the weight of the ice was removed. The amount of isostatic rebound since the last ice age
is approximately 650 metres. Effect of climate warming
The Tibetan Plateau contains the world's third-largest store of ice. Qin Dahe, the former head of
the China Meteorological Administration, said that the recent fast pace of melting and warmer
temperatures will be good for agriculture and tourism in the short term; but issued
a strong warning:
"Temperatures are rising four times faster than elsewhere in China, and the Tibetan glaciers
are retreating at a higher speed than in any other part of the world." "In the short term,
this will cause lakes to expand and bring floods and mudflows." "In the long run, the
glaciers are vital lifelines for Asian rivers, including the Indus and the Ganges. Once they
vanish, water supplies in those regions will be in peril."
In popular culture Zhang Qianyi composed a song about the Tibetan
plateau, named 青藏高原, which is performed by both Han Hong and subsequently by Russian
singer Vitas. In the Teen Titans animated series, the superhero
Jericho lives atop a mountain in Tibet, living an isolated lifestyle. However, Jericho only
appeared on his mountain in one episode. See also
Geography of Tibet Geology of the Himalaya
Changtang Taklamakan Desert
Yunnan-Guizhou Plateau Lop Nur
Kingdom of Tibet Notes
References Hopkirk, Peter. Trespassers on the Roof of
the World: The Secret Exploration of Tibet. J. P. Tarcher. ISBN 0-87477-257-5.
Brantingham, P. J. & Xing, G.. "Peopling of the northern Tibetan Plateau". World Archaeology
38: 387–414. doi:10.1080/00438240600813301. External links
ON THINNER ICE 如履薄冰 The End of Earth's Summer
Long Rivers and Distant Sources "Roof of the Earth" Offers Clues About How
Our Planet Was Shaped Plateau Perspectives
Leaf morphology and the timing of the rise of the Tibetan Plateau
Todays weather in the eastern Chang Tang Protected areas of the Tibetan Plateau region
"North Tibetan Plateau-Kunlun Mountains alpine desert". Terrestrial Ecoregions. World Wildlife
Fund. Photos of Tibetan nomads
"Roof of the Earth" Offers Clues About How Our Planet Was Shaped
Contemporary lifestyle and language learning center from Tibet lhasa, the official language
of Tibetan. podcast.