Lake Van (; ; ) is the largest lake in Turkey. It lies in the far east of Turkey, in the provinces of Van and Bitlis in the Armenian highlands. It is a saline soda lake, receiving water from many small streams that descend from the surrounding mountains. It is one of the world's few endorheic lakes (a lake having no outlet) of size greater than and has 38% of the country's surface water (including rivers). A volcanic eruption blocked its original outlet in prehistoric times. It is situated at above sea level. Despite the high altitude and winter highs below , high salinity usually prevents it from freezing; the shallow northern section can freeze, but rarely. Hydrology and chemistry Lake Van is across at its widest point. It averages deep. Its greatest known depth is . The surface lies above sea level and the shore length is . It covers and contains (has volume of) . The western portion of the lake is deepest, with a large basin deeper than 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 on its northwest side where it joins the rest of the lake. The Erciş arm is much shallower, mostly less than , with a maximum depth of about . The lake water is strongly alkaline (pH 9.7–9.8) and rich in sodium carbonate and other salts. Some is extracted in salt evaporation ponds alongside, used in or as detergents. Geology Lake Van is primarily a tectonic lake, formed more than 600,000 years ago by the gradual subsidence of a large block of the earth's crust due to movement on several major faults that run through this portion of Eastern Anatolia. The lake's southern margin demarcates: a metamorphic rock zone of the Bitlis Massif and volcanic strata of the Neogene and Quaternary periods. The deep, western portion of the lake is an antidome basin in a tectonic depression. This was formed by normal and strike-slip faulting and thrusting. The lake's proximity to the Karlıova Triple Junction has led to molten fluids of the Earth's mantle accumulating in the strata beneath, still driving gradual change. Dominating the lake's northern shore is the stratovolcano Mount Süphan. The broad crater of a second, dormant volcano, Mount Nemrut, is close to the western tip of the lake. There