The Qarhan Playa or Salt Plain, also misleadingly described as Qarhan Lake, is a playa in the Golmud and Dulan counties of Haixi Prefecture, Qinghai, China. Formerly a single unitary lake, it is now an expansive salt flat divided into four greater sections (Dabusun, Big/Small Bieletan, Suli, and N./S. Huoluxun) which contain a number of smaller salt lakes, the largest of which is Dabusun Lake. The area is heavily exploited for its valuable salt, mineral, and rare earth reserves but parts are also protected as a national park and contribute to regional tourism.
Name Qarhan is the GNC romanization of the area's Mongolian name, originally derived from the word for "white" (Modern Mongolian: цагаан, tsagaan, or ᠴᠠᠭᠠᠨ, čaɣan). Cha'erhan is the pinyin romanization of the Mandarin pronunciation of 察爾汗, a modification of the original transcription into Chinese characters of the same name; it is also sometimes clipped into Charhan in English sources. The Chinese name, which does not distinguish between actual salt lakes and playas, also causes the playa to be called a "lake" or even "the largest salt lake in China" in less careful English sources.
Geography The Qarhan Playa covers an area of 5,856 km2 (2,261 sq mi), stretching over 160 km (100 mi) east to west and usually between 20–40 km (12–25 mi) north to south. The southwest lies in Golmud and the northeast in Dulan County, both in Haixi Prefecture, Qinghai, China. The roughly 60,000 km2 (23,000 sq mi) area of Qarhan inclusive of Taijinar to its west is sometimes known as the Sanhu ("Three Lakes"), after the two Taijinar lakes, Suli Lake, and Dabusun. Qarhan is part of the larger Qaidam Basin, lying between the Kunlun Mountains to the south, the Altun to the west, and the Qilian to the north. Qarhan's lakes lie between 2,675–2,680 m (8,780–8,790 ft) above sea level, with Dabusun and North Hulsan being the lowest and Xiezuo being the highest. The effect of elevation is such that despite lying on the same latitude as Greece, Algeria, and Virginia in the United States, Qarhan has a mean annual temperature of 0.1 °C (32.2 °F). The mean air speed is 4.3 m/s (9.6 mph), and the mean relative humidity is 27.7%. In the playa's hyperarid climate, there is generally only 28–40 mm (1–2 in) of annual rainfall but 3,000–3,564 mm (118.1–140.3 in) of annual evaporation. Despite this, meltwater rivers and mineral springs fill the basins of the salt flat's four main sections—Bieletan, Dabusun, Qarhan, and Huoluxun—with about ten large but shallow lakes usually collectively occupying an area of about 460 km2 (180 sq mi): Suli Lake in the west, fed from the west by the Urt Moron; the Little and Big Biele Lakes beside it, fed from the south by the Tuolahai and Qingshui Rivers; West Dabusun and Dabusun Lake (the largest), in the center, fed from the south by the Golmud River; Dongling Lake to their northwest; Xiezuo and Tuanjie Lakes to their east, fed respectively by the intermittent Quanji and Shougong Rivers; and North and South Hulsan Lakes at the east end of the playa, fed from the east by the Qaidam, Nuomuhong, and Suolinguole Rivers. All of these are usually less than 1 m (3 ft 3 in) deep. There are also some ephemeral lakes. Most of the streams contributing to these lakes flow north into the playa from the Kunlun and its foothills. The Golmud River is the main contributor, providing a mean annual influx of 19.2 trillion L (5.07 trillion gal) of water. There is also contribution of about 1% from mineral springs, especially on the north end of the playa, which play an important role in the chemical composition of the sediment. The local flora consists of sparse forbs (particularly members of Chenopodioideae) and shrubs, especially members of Ephedra and Tamarix.
Geology Most of the Qarhan Playa is solid halite underlain by a layer of brine to about 1.3 m (4 ft 3 in) under the soil, and it holds enormous reserves of salt, with solid layers extending between 2–20 m (6 ft 7 in – 65 ft 7 in). The 50 billion metric tons (55 billion short tons) are estimated sufficient to meet present world demand for 1,000 years. The area around Dabusun Lake has halite to depths of at least 40 m (130 ft), although with alternating layers of mud in places. The salinity of the playa's lakes varies between 164.81 and 359.50 g/L (1.3–3 lb/gal); their pH values are between 5.4 and 7.85. Other minerals include potash, carnallite (potassium magnesium chloride), calcium chloride, magnesium, lithium, boron, iodine, and sylvite. The basin is one of China's richest sources for potassium, with an estimated 360 million metric tons (400 million short tons) of potassium oxide. Its reserves are also important as the world's largest present-day accumulation of potassium-rich salt in the world, which helped scientists better understand the chemical and evaporation pathways involved in the creation of natural potash and disprove previous suppositions that it only formed in marine environments. The Bieletan subbasin in the west is the richest source of brine lithium in China, with an estimated reserve of 7.74 million metric tons (8.53 million short tons) of lithium chloride. The Sanhu as a whole holds 83% of the country's known lithium reserves, with some areas having concentrations of 330 ppm.
History
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