Lop Nur

Lop Nur or Lop Nor (Uyghur: لوپنۇر, Oirat: ᠯᠣ᠊ᠫ
ᠨᡇᡇᠷ, romanized: Lob nuur, from an Oirat Mongolic name meaning "Lop Lake", where "Lop" is a toponym of unknown origin) is a now largely dried-up salt lake formerly located within the Lop Depression in the eastern fringe of the Tarim Basin in the southeastern portion of the Xinjiang Autonomous Region, northwestern China, between the Taklamakan and Kumtag deserts. Administratively, the lake is in Lop Nur town (Chinese: 罗布泊镇; pinyin: Luóbùpō zhèn), also known as Luozhong (罗中; Luózhōng) of Ruoqiang County, which in its turn is part of the Bayingolin Mongol Autonomous Prefecture.

The lake system, into which the Tarim River and Shule River drain from the west and east respectively, is the last remnant of the historical post-glacial Tarim Lake, which once covered more than 10,000 km² (3,900 sq mi) in the Tarim Basin but had progressively shrunk throughout the Holocene due to rain shadowing by the Tibetan Plateau. Lop Nur is hydrologically endorheic, it is landbound and has no outlet, and has relied largely on meltwater runoffs from the Tianshan, Kunlun and the western Qilian Mountains. The lake measured 3,100 km² (1,200 sq mi) in 1928, but has dried up due to construction of reservoirs which dammed the flow of water feeding into the lake, and only small seasonal lakes and salt marshes may form. The dried-up Lop Nur Basin is covered with a salt crust ranging from 30 to 100 cm (12 to 39 in) in thickness.

An area to the northwest of Lop Nur has been used as a nuclear testing site. Since the discovery of potash at the site in the mid-1990s, it is also the location of a large-scale mining operation. There are some restricted areas under military management and cultural relics protection points in the region, which are not open to the public.

From around 1800 BC until the 9th century the lake supported a thriving Tocharian culture. Archaeologists have discovered the buried remains of settlements, as well as several of the Tarim mummies, along its ancient shoreline. Former water resources of the Tarim River and Lop Nur nurtured the kingdom of Loulan since the second century BC, an ancient civilisation along the Silk Road, which skirted the lake-filled basin. Loulan became a client state of the Chinese empire in 55 BC, renamed Shanshan. Faxian went by the Lop Desert on his way to the Indus valley (395–414), followed by later Chinese pilgrims. Marco Polo in his travels passed through the Lop Desert. In the 19th century and early 20th century, the explorers Ferdinand von Richthofen, Nikolai Przhevalsky, Sven Hedin and Aurel Stein visited and studied the area. It is also likely that Swedish soldier Johan Gustaf Renat had visited the area when he was helping the Zunghars to produce maps over the area in the eighteenth century.

The lake was given various names in ancient Chinese texts. In Shiji it was called Yan Ze (鹽澤, literally Salt Marsh), indicating its saline nature, near which was located the ancient Loulan Kingdom. In Hanshu it was called Puchang Hai (蒲昌海, literally Sea of Abundant Reed) and was given a dimension of 300 to 400 li (roughly 120–160 km) in length and breadth, indicating it was once a lake of great size. These early texts also mentioned the belief, mistaken as it turns out, that the lake joins the Yellow River at Jishi through an underground channel as the source of the river.

The lake was referred to as the "Wandering Lake" in the early 20th century due to the Tarim River changing its course, causing its terminal lake to alter its location between the Lop Nur dried basin, the Kara-Koshun dried basin and the Taitema Lake basin. This shift of the terminal lake caused some confusion amongst the early explorers as to the exact location of Lop Nur. Imperial maps from the Qing dynasty showed Lop Nur to be located in similar position to the present Lop Nur dried basin, but the Russian geographer Nikolay Przhevalsky instead found the terminal lake at Kara-Koshun in 1867. Sven Hedin visited the area in 1900–1901 and suggested that the Tarim river periodically changed its course to and from between its southbound and northbound direction, resulting in a shift in the position of the terminal lake. The change in the course of the river, which resulted in Lop Nur drying up, was also suggested by Hedin as the reason why ancient settlements such as Loulan had perished.

In 1921, due to human intervention, the terminal lake shifted its position back to Lop Nur. The lake measured 2400 km² in area in 1930–1931. In 1934, Sven Hedin went down the new Kuruk Darya ("Dry River") in a canoe. He found the delta to be a maze of channels and the new lake so shallow that it was difficult to navigate even in a canoe. He had previously walked the dry Kuruk Darya in a caravan in 1900.

In 1952 the terminal lake then shifted to Taitema Lake when the Tarim River and Konque River were separated through human intervention, and Lop Nur dried out again by 1964. In 1972, the Daxihaizi Reservoir was built at Tikanlik, water supply to the lake was cut off, and all the lakes for the most part then dried out, with only small seasonal lakes forming in local depressions in Taitema. The loss of water to the lower Tarim River Valley also led to the deterioration and loss of poplar forests and tamarix shrubs that used to be extensively distributed along the lower Tarim River Valley forming the so-called "Green Corridor". In 2000, in an effort to prevent further deterioration of the ecosystem, water was diverted from Lake Bosten in an attempt to fill the Taitema Lake. The Taitema Lake however had shifted 30 to 40 kilometres (19 to 25 mi) westwards during the past 40 years due in part to the spread of the desert. Another cause of the destabilization of the desert has been the cutting of poplars and willows for firewood; in response, a restoration project to reclaim the poplar forests was initiated.