Lake Van
Lake Van is the largest lake in Turkey. It lies in the Eastern Anatolia region 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 of size greater than and has 38% of the country's surface water. A volcanic eruption blocked its original outlet in prehistoric times. It is situated at above sea level. Despite the high altitude and winter averages 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 .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 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 is hydrothermal activity throughout the region.
For much of its history, until the Pleistocene, Lake Van has had an outlet towards the southwest. However, the level of this threshold has varied over time, as the lake has been blocked by successive lava flows from Nemrut volcano westward towards the Muş Plain. This threshold has then been lowered at times by erosion.
Bathymetry
The first acoustic survey of Lake Van was performed in 1974.Kempe and Degens later identified three physiographic provinces comprising the lake:
- a lacustrine shelf from the shore to a clear gradient change
- a steeper lacustrine slope
- a deep, relatively flat basin province in the western center of the lake.
Prehistoric lake levels
Land terraces above the present shore have long been recognized. On a visit in 1898, geologist Felix Oswald noted three raised beaches at 5, 15, and 30 m above the lake then, as well as recently drowned trees. Research in the past century has identified many similar terraces, and the lake's level has fluctuated significantly during that time.Image:Çadır Dağı seen from the island of Akdamar in lake Van.jpg|right|thumb|The dormant volcano Mount Çadır viewed from Akdamar Island
In 1989 and 1990, an international team of geologists led by Stephan Kempe from the University of Hamburg retrieved ten sediment cores from depths up to. 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.
The PALEOVAN project has studied in detail the paleolimnology, paleoclimatology, and sedimentology of Lake Van over the last 600,000 years by using seismic reflection and continuous cores recovered from deep borings. These techniques along with investigation of the chronology and sedimentology of associated onshore terraces have been used to reconstruct past climatic, volcanic, and tectonic activity since the formation of Lake Van about 600,000 years ago when a single pull-apart basin was separated into Van and Mus basins by the eruptions of the Nemrut Volcano which also blocked Lake Van's outlet.
The PALEOVAN project found that the lake level of Lake Van has varied by as much as during the past 600,000 years. During this period of time, five major lowstands of lake level occurred circa 600, 365–340, 290–230, 150–130, and 30–14 ka BP. Between 600 and 230 ka BP, the lake varied dramatically, by hundreds of meters. The occurrence of major lowstands of Lake Van during glacial periods suggest regional paleoclimate, i.e. greatly reduced precipitation, was the dominant cause for the dramatic changes in lake level of Lake Van. However, volcanic and tectonic forcing factors may have contributed to lake level changes as well.
Over the last 90,000 years, significant variations in the lake level of Lake Van have been inferred based on the presence of lowstand deltas and onlap sequences in seismic reflection profiles; the analysis of data extracted PALEOVAN cores; and studies of coastal terraces of differing elevations. First, a major lowstand of below modern lake level occurred between 71 and 59 ka BP as inferred from the presence of lowstand deltas and onlap sequences in seismic reflection profiles. Between 60 and 34 ka BP., the lake level of Lake Van was in general lower than the modern lake level with highstands at 57, 53, 46 and 35 ka BP. About 34 ka BP, a dramatic rise in lake level to about above the present lake level occurred as indicated by the formation of terraces circa above present-day lake level and the presence of onlapping seismic onlap sequences. This rapid rise in lake level was likely either the result of increased melt water delivery or the deposition of a large quantities of tephra and lahars created during a caldera forming eruption of Mount Nemrut. Two terraces dated at 26 to 24.5 and 21 to 20 ka BP reaching above the present lake level and the occurrence of lowstand deltas and onlap sequences in the seismic reflection profiles indicate high lake levels during the end of Last Glacial period. These two terraces were likely deposited during the interstadial events. Between 16 and 15 ka BP, the complete desiccation of Lake Van dropped lake levels to m below modern levels. By the Bøllinge-Allerød period, lake levels were possibly similar to or little lower than the modern lake level. During the Younger Dryas cold period lake levels dropped to lower than the modern level. The early Holocene was characterized by variable lake levels above and below modern with amplitudes of a few tens of meters. These variations in lake levels during the Holocene are indicated by the presence of early to middle Holocene terraces near river mouths,
Recent lake level change
Similar but smaller fluctuations have been seen recently. The level of the lake rose by at least during the 1990s, drowning much agricultural land, and seems to be rising again. The level rose approximately in the 10 years immediately prior to 2004. But in the early 2020s it fell.Climate
Lake Van is in the highest and largest region of Turkey, which has a Mediterranean-influenced humid continental climate. Average temperatures in July are between 22 and 25 °C, and in January between −3 °C and −12 °C. On some cold winter nights the temperature has reached −30 °C.The lake, particularly on its urban townscape shore, tempers the climate in the city of Van, where the average temperature in July is 22.5 °C, and in January −3.5 °C. The average annual rainfall in the basin ranges from 400 to 700 mm.
Ecology
Prior to 2018, the only fish known to live in the brackish water of Lake Van was Alburnus tarichi or Pearl Mullet, a Cyprinid fish related to chub and dace, which is caught during the spring floods. In May and June, these fish migrate from the lake to less alkaline water, spawning either near the mouths of the rivers feeding the lake or in the rivers themselves. After spawning season it returns to the lake. In 2018, a new species of fish, which is deemed as Oxynoemacheilus ercisianus, has been discovered inside a microbialite.103 species of phytoplankton have been recorded in the lake including cyanobacteria, flagellates, diatoms, green algae, and brown algae. 36 species of zooplankton have also been recorded including Rotatoria, Cladocera, and Copepoda in the lake.
In 1991, researchers reported the discovery of tall microbialites in the lake. These are solid towers on the lake bed formed by coccoid cyanobacteria, which create mats of aragonite that combine with calcite precipitating out of the lake water.
The region hosts the rare Van cat breed of cat, having - among other things - an unusual fascination with water. The lake is mainly surrounded by fruit orchards and grain fields, interspersed by some non-agricultural trees.
Monster myth
According to legend, the lake hosts the mysterious Lake Van Monster that lurks below the surface, long with brown scaly skin, an elongated reptilian head and flippers. Apart from some inconclusive amateur photographs and videos, there has never been any evidence of it. The claimed profile resembles an extinct mosasaurus or basilosaurus.History
, the capital of Urartu, near the shores, on the site of what became medieval Van's castle, west of present-day Van city. The ruins of the medieval city of Van are still visible below the southern slopes of the rock on which Van Castle stands.In 2017, archaeologists from Van Yüzüncü Yil University and a team of independent divers who were exploring Lake Van reported the discovery of a large underwater fortress spanning roughly one kilometer. The team estimates that this fortress was constructed during the Urartian period, based on their visual assessments. The archaeologists believe that the fortress, along with other parts of the ancient city that surrounded it at the time, had slowly become submerged over the millennia by the gradually rising lake.