Lake Van the largest lake in Turkey, lies in the far east of that country in the provinces of Van and Bitlis. It is a saline soda lake, receiving water from numerous small streams that descend from the surrounding mountains. Lake Van is one of the world's largest endorheic lakes (having no outlet) – a volcanic eruption blocked the original outlet from the basin in ancient times. Although Lake Van has an altitude of 1,640 m (5,380 ft) in a region with harsh winters, its high salinity prevents most of it from freezing, and even the shallow northern section freezes only rarely.
Lake Van is 119 kilometres (74 mi) across at its widest point, averaging a depth of 171 metres (561 ft) with a maximum recorded depth of 451 metres (1,480 ft). The lake surface lies 1,640 metres (5,380 ft) above sea level and the shore length is 430 kilometres (270 mi). Lake Van has an area of 3,755 km2 (1,450 sq mi) and a volume of 607 cubic kilometres (146 cu mi). The western portion of the lake is deepest, with a large basin deeper than 400 m (1,300 ft) lying northeast of Tatvan and south of Ahlat. The eastern arms of the lake are shallower. The Van-Ahtamar portion shelves gradually, with a maximum depth of about 250 m (820 ft) on its northwest side where it joins the rest of the lake. The Erciş arm is much shallower, mostly less than 50 m (160 ft), with a maximum depth of about 150 m (490 ft). The lake water is strongly alkaline (pH 9.7–9.8) and rich in sodium carbonate and other salts, which are extracted by evaporation and used as detergents.
The lake's outlet was blocked at some time during the Pleistocene, when lava flows from Nemrut volcano blocked westward outflow towards the Muş Plain. Now dormant, Nemrut Dağı is close to the western shore of the lake, and another dormant stratovolcano, Süphan Dağı dominates the northern side of the lake. The water level of the lake has often altered dramatically: near Tatvan, Felix Oswald (see Geology of Armenia, 1901) noted a raised beach high above the present level of the lake as well as recently drowned trees. Investigation by Degens and others in the early 1980s determined that the highest lake levels (72 metres (236 ft) above the current height) had been during the last ice age, about 18,000 years ago. Approximately 9,500 years ago there was a dramatic drop to more than 300 metres (980 ft) below the present level. This was followed by an equally-dramatic rise around 6,500 years ago.
In 1989 and 1990, an international team of geologists led by Dr. Stephan Kempe from the University of Hamburg (now Professor at the Technische Universität Darmstadt) retrieved ten sediment cores from depths up to 446 m (1,463 ft). Although these cores only penetrated the first few meters of sediment, they provided sufficient varves to give proxy climate data for up to 14,570 years BP. A team of scientists headed by palaeontologist Professor Thomas Litt at the University of Bonn has applied for funding from the International Continental Scientific Drilling Program (ICDP) for a new, deeper-drilling project to examine the lake's sediments. Litt expects to find that "Lake Van stores the climate history of the last 800,000 years—an incomparable treasure house of data which we want to tap for at least the last 500,000 years." A test drilling in 2004 detected evidence of 15 volcanic eruptions in the past 20,000 years.
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