Salween River
Geology

The present course of the Salween began to form about 5 million years ago as the Indian subcontinent collided with Asia, resulting in the uplift of the Himalaya mountains and the Tibetan Plateau. Prior to the Himalaya orogeny, what are now the upper Irrawaddy, Salween, Mekong and Yangtze rivers may have all flowed into the Red River, emptying into the South China Sea. The landscape was hilly but not particularly rugged, with average elevations of 1,000 m (3,300 ft) or less. As the continents converged, a complex jumble of mountains arose, breaking the ancestral Red into different drainage systems, with the Yangtze heading east towards the Pacific, and the Mekong and Salween flowing south into what is now Thailand's Chao Phraya River. About 1.5 million years ago, volcanic activity diverted the Salween west towards the Andaman Sea, roughly creating the modern path of the river.

The parallel modern courses of the upper Salween, Mekong and Yangtze are located where the eastern Tibetan Plateau intersects the uplands of the Yunnan-Guizhou Plateau. The mountain ranges separating these rivers are individual terranes (crustal fragments) that accreted separately to the Asian continent – forming a basin and range landscape with drainage running from north to south – then compressed together such that the rivers flow only 20 km (12 mi) apart in places. As the mountains continued to rise, the rivers incised into the landscape along parallel fault zones, creating the deep canyons of the present day. The Nujiang fault zone stretches over 600 km (370 mi) along the river in Yunnan.

The formation of the Himalayas blocked drainage from the Tibetan Plateau south towards the Indian Ocean, forcing drainage north of the mountains east towards the Yangtze river. This east-flowing river, the predecessor of the modern Yarlung Tsangpo river, was repeatedly captured into drainages to the south, finding various routes to the sea via the Red, Mekong, Salween and Irrawaddy rivers. The combined Salween–Yarlung Tsangpo drainage would have been much longer than the modern Salween, stretching an additional 1,500 km (930 mi) west across the Tibetan Plateau. Ultimately the Yarlung Tsangpo was captured by the Brahmaputra River in present-day India. The Salween may once have had additional tributaries above its present source, but due to the uplift of the Himalaya blocking moisture from the Indian Ocean, these tributaries dried up, leaving the numerous terminal lakes scattered across Nagqu today.

The Salween carries an estimated 108 to 237 million tonnes of sediment per year. About 92 percent of sediment is delivered to the ocean during the monsoon season. The Salween delta is physically contiguous with the Irrawaddy and Sittaung deltas. The Irrawaddy–Sittaung–Salween delta is relatively stable, with the coastline advancing an average of 3.4 m (11 ft) per year between 1925 and 2006. Sediment accumulation is largely balanced out by subsidence and transport by ocean currents. However, proposed dams along the Salween would trap much of the sediment with potential detrimental impacts to coastal erosion.
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