Tibet is bounded on the north and east by China Proper, on the west by the Kashmir Region of India and on the south by Nepal, India and Bhutan. Most of Tibet sits atop a geological structure known as the Tibetan Plateau which includes the Himalaya and many of the highest mountain peaks in the world.
High mountain peaks include Changtse, Lhotse, Makalu, Gauri Sankar, Gurla Mandhata Cho Oyu, Jomolhari, Gyachung Kang, Gyala Peri, Mount Kailash, Kawagebo, Khumbutse, Melungtse, Mount Nyainqentanglha Namcha Barwa, Mount Nyainqentanglha, Shishapangma and Yangra . Mountain passes include Cherko la, and North Col. Smaller mountains include Mount Gephel and Gurla Mandhata.
Physically, Tibet may be divided into two parts, the "lake region" in the west and north-west, and the "river region", which spreads out on three sides of the former on the east, south, and west. Both regions receive limited amounts of rainfall as they lie in the rain shadow of the Himalayas, however the region names are useful in contrasting their hydrological structures, and also in contrasting their different cultural uses which is nomadic in the lake region and agricultural in the river region. On the south it is bounded by the Himalayas, on the north by a broad mountain system. The system at no point narrows to a single range; generally there are three or four across its breadth. As a whole the system forms the watershed between rivers flowing to the Indian Ocean �C the Indus, Brahmaputra and Salween and its tributaries �C and the streams flowing into the undrained salt lakes to the north.
The lake region extends from the Pangong Tso Lake in Ladakh, Lake Rakshastal, Yamdrok Lake and Lake Manasarovar near the source of the Indus River, to the sources of the Salween, the Mekong and the Yangtze. Other lakes include Dagze Co, Nam Co, and Pagsum Co. The lake region is an arid and wind-swept desert. This region is called the Chang Tang (Byang sang) or 'Northern Plateau' by the people of Tibet. It is some 1100 km (700 mi) broad, and covers an area about equal to that of France. Due to its great distance from the ocean it is extremely arid and possesses no river outlet. The mountain ranges are spread out, rounded, disconnected, separated by flat valleys relatively of little depth. The country is dotted over with large and small lakes, generally salt or alkaline, and intersected by streams. Due to the presence of discontinuous permafrost over the Chang Tang, the soil is boggy and covered with tussocks of grass, thus resembling the Siberian tundra. Salt and fresh-water lakes are intermingled. The lakes are generally without outlet, or have only a small effluent. The deposits consist of soda, potash, borax and common salt. The lake region is noted for a vast number of hot springs, which are widely distributed between the Himalaya and 34�� N., but are most numerous to the west of Tengri Nor (north-west of Lhasa). So intense is the cold in this part of Tibet that these springs are sometimes represented by columns of ice, the nearly boiling water having frozen in the act of ejection.
The river region is characterized by fertile mountain valleys and includes the Yarlung Tsangpo River (the upper courses of the Brahmaputra) and its major tributary, the Nyang River, the Salween, the Yangtze, the Mekong, and the Yellow River. The Yarlung Tsangpo Canyon, formed by a horseshoe bend in the river where it flows around Namcha Barwa, is the deepest, and possibly longest canyon in the world. Among the mountains there are many narrow valleys. The valleys of Lhasa, Shigatse, Gyantse and the Brahmaputra are free from permafrost, covered with good soil and groves of trees, well irrigated, and richly cultivated.
The South Tibet Valley is formed by the Yarlung Zangbo River during its middle reaches, where it travels from west to east. The valley is approximately 1200 kilometres long and 300 kilometres wide. The valley descends from 4500 metres above sea level to 2800 metres. The mountains on either side of the valley are usually around 5000 metres high. Lakes here include Lake Paiku and Lake Puma Yumco.