Geography

Even though the roof of the world has existed for uncountable years, in geological terms, the creation of the Himalayas and the rising of the Tibetan plateau are extremely recent events. The mountains originated less than four million years ago, making them among the youngest in the world.
About 80 million years ago India broke away from an early massive protocontinent. Slowly and steadily it moved across the ancient Sea of Tethys, collecting hard sheets of rock along the way. Eventually it rammed into the soft underside of Asia, which the rock easily penetrated and pushed up, creating the Himalayas. From sea level these mountains rose rapidly to a height of nearly 9,000 meters. Today the succession of parallel ranges, running east to west for nearly 3,200 kilometers, reveals this original plate boundary between India and Asia. In fact, the movement of sub-continental India is still forcing the Himalayas upwards at a rate of two centimeters per year in places.
The rivers of Tibet existed before the collision of India and Asia. As the soft sedimentary rocks that formed the bottom of the Sea of Tethys were folded up, the rivers were able to cut through them and maintain their original north-to-south course. As a result there are many spectacular gorges and mountain ranges sliced up into individual massifs.
Much of Tibet, once well-forested, lush and fertile, is today one of the world's most unforgiving places. As the Himalayas increased in height, less and less moisture reached the areas north of the range. The result has been a slow botanical death to the great northern plateau, the desertification of huge regions of Tibet and Xinjiang.
There are three distinct geographical regions in Tibet. By far the largest natural region is the northern plateau. It covers about half of Tibet's total surface area and there is little rainfall and no outlet for the rivers. As a result, the region is characterized by myriad salty and brackish lakes.
These factors-constant wind, low rainfall and salt in the soil-severely limit the types of plant life that can survive, these being mostly grasses and herbs. There are fewer than 60 species of flowering plants, only three of which are woody.
The second main geographical region of Tibet, the outer plateau, extends in a great arc for nearly 3,500 kilometers. It is a relatively narrow strip, with the Himalayas forming the southern boundary. It is the most populous part of Tibet and contains almost all the major human settlements.
The outer plateau differs from the northern plateau in several important ways. First, the temperature and climate are milder, and consequently there is a richer distribution of flora and fauna. Secondly, agriculture exists in the outer plateau in many old and well-developed agricultural regions. The area around Shigatse and the Lhasa Valley are clear examples of this. Contrary to popular images of Tibet, Lhasa has a pleasant climate, with nearly all its rainfall occurring in the summer. For most of the year the weather is sunny and dry, mild during the day from April to October, and not unbearably cold in winter.
In the west, the outer plateau is an expanse of gravelly land, where vegetation is poor, but in the east it becomes a grassy steppe, running all the way to the Yellow River, where there is more rainfall, warmer weather and significantly more vegetation.
The other main geographical region is the southeastern plateau, comprising only one-tenth of the total area of Tibet. Plant and animal life here is vastly richer than in the other regions. Forests are very muck a characteristic of the southeastern plateau; its western and northern boundaries follow the natural limits of trees.
The transition from the outer plateau to the southeastern plateau is gradual, though marked by a steady increase in trees and a decline in altitude. The lowest point in Tibet is near the great bend of the Yarlong Tsangpo as it turns southward towards India. This region has an abundance of alpine and tropical plants such as laurel, rhododendron, azalea, bamboo, magnolia, oak, and even tea and banana, most of which appear in or near dense, moist evergreen forests.
The most dramatic geographical phenomena here are the deep river gorges formed by the upper reaches of the Salween, the Mekong and the Yangzi, three of Asia's mightiest rivers. These gorges erode and dissect the land, allowing moisture bearing winds of the summer monsoon to reach the southeastern plateau.
Many animal groups are impoverished by the high altitude and severe climate of Tibet. There are very few amphibians or reptiles, limiting the number of insectivorous birds, moles and shrews. Fish are generally members of the salmon and carp family. They abound in rivers and some large lakes, such as Namtso, but many lakes have so much salt that no fish at all can survive.
Most of the animals of the northern and outer plateau are desert and steppe species. These animals are well adapted to the harsh conditions and wide open landscapes, which require them to migrate long distances in search of food.
The shaggy, powerful yak is a shining example of animal adaptation to the awful demands of Tibet. Another typical animal is the wild ass. It often gathers in large herds, especially in western Tibet, and makes extremely long journeys in search of pasture. The wild ass is the fastest runner on the plateau. Another remarkable and very beautiful beast is the Tibetan antelope, outstanding for its long, thin, almost vertical horns, which can attain 70 centimeters in length.
The most numerous mammals in Tibet are rodents, which are ubiquitous wherever there is sufficient plant material to support them. Predators such as wolves, foxes and bears rely to a large extent on these rodents. Another predator, and perhaps the most magnificent of all Tibet's creatures, is the extremely rare snow leopard.
More than 500 species of birds have been recorded in Tibet, and even the most casual observer can easily identify 20 or 30 separate varieties. This number can quickly be doubled with a bit of careful study or just a visit to one of Tibet's great Lakes.
Anyway, as soon as the great plateau comes into your eyes, you will be full occupied by everything belonging to her.