Editing Lake Van (section)

==Geology==
{{image frame|content={{Van lake map|font-size=85%}}|width=370|align=right|caption=Lakes near Lake Van.}}
Lake Van is primarily a [[Lake#Tectonic lakes|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 fault|normal]] and [[strike-slip fault|strike-slip]] faulting and thrusting.{{sfn|Toker|Sengör|Filiz|Demirbağ|2017|p=166}}

The lake's proximity to the [[Karlıova triple junction]] has led to molten fluids of the Earth's [[mantle (geology)|mantle]] accumulating in the strata beneath, still driving gradual change.{{sfn|Toker|Sengör|Filiz|Demirbağ|2017|p=166}} Dominating the lake's northern shore is the [[stratovolcano]] [[Mount Süphan]]. The broad crater of a second, dormant volcano, [[Nemrut (volcano)|Mount Nemrut]], is close to the western tip of the lake. There is hydrothermal activity throughout the region.{{sfn|Toker|Sengör|Filiz|Demirbağ|2017|p=166}}

For much of its history, until the [[Pleistocene]], Lake Van has had an outlet towards the southwest (into the [[Murat River]] and eventually into the [[Euphrates river]]). However, the level of this threshold has varied over time, as the lake has been blocked by successive [[lava flows]] from [[Nemrut (volcano)|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.{{sfn|Wong|Degens|1978}}{{sfn|Toker|Sengör|Filiz|Demirbağ|2017|p=167}}

Kempe and Degens later identified three physiographic provinces comprising the lake: 
*a lacustrine shelf (27% of the lake) from the shore to a clear gradient change
*a steeper lacustrine slope (63%)
*a deep, relatively flat basin province (10%) in the western center of the lake.{{sfn|Kempe|Degens|1978}}

The deepest part of the lake is the Tatvan basin, which is almost completely bounded by faults.{{sfn|Toker|Sengör|Filiz|Demirbağ|2017|p=167}}

===Prehistoric lake levels===
[[File:Old beach lines shown on section of north rim of Sheikh Ora volcano near Tatvan Felix Oswald Geology of Armenia 1906 p103f-b (cropped).png|thumb|Section of north rim of the Sheikh Ora crater, showing old beach lines, drawn by Felix Oswald, 1906]]
[[File:Turkey, Van Lake 10.jpg|thumb|left|200px|View of Lake Van from the air.]]
Land terraces (remnant dry, upper banks from previous shorelines) above the present shore have long been recognized. On a visit in 1898, geologist [[Felix Oswald (archaeologist)|Felix Oswald]] noted three raised beaches at 15, 50 and 100 feet (5, 15 and 30 meters) above the lake then, as well as recently drowned trees.{{sfn|Oswald|1906|pp=102–103}} Research in the past century has identified many similar terraces, and the lake's level has fluctuated significantly during that time.

As the lake has no outlet, the level over recent millennia rests on inflow and evaporation.

The water level has vacillated greatly. Investigation by a team including Degens in the early 1980s determined that the highest lake levels ({{convert|72|m}} 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 {{convert|300|m}} below the present level. This was followed by an equally-dramatic rise around 6,500 years ago.{{sfn|Degens|Wong|Kempe|Kurtman|1984}}

As a deep lake with no outlet, Lake Van has accumulated great amounts of sediment washed in from surrounding plains and valleys, and occasionally deposited as ash from eruptions of nearby volcanoes.
This layer of sediment is estimated to be up to {{convert|400|m}} thick in places, and has attracted climatologists and vulcanologists interested in drilling cores to examine the layered sediments.

[[Image:Çadır Dağı seen from the island of Akdamar in lake Van.jpg|right|thumb|The dormant volcano [[Mount Artos|Mount Çadır]] viewed from [[Akdamar Island]]]]
In 1989 and 1990, an international team of geologists led by Stephan Kempe from the University of Hamburg{{efn|Later Professor at the Technische Universität Darmstadt}} retrieved ten sediment cores from depths up to {{convert|446|m|ft|abbr=on}}. 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 [[Before Present|BP]].{{sfn|Landmann|Reimera|Lemcke|Kempe|1996}}

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 an akin deeper-drilling project. This expects to find it "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."{{sfn|University of Bonn|2007}} A test drilling in 2004 detected evidence of 15 volcanic eruptions in the past 20,000 years.

===Recent lake level change===
Similar but smaller fluctuations have been seen recently. The level of the lake rose by at least {{cvt|3|m|ft}} during the 1990s, drowning much agricultural land, and (after a brief period of stability and then retreat) seems to be rising again. The level rose approximately {{cvt|2|m|ft}} in the 10 years immediately prior to 2004.{{sfn|Coskun|Musaoğlu|2004}} But in the early 2020s it fell.<ref>{{Cite web |title=Recession continues in Turkey's largest lake |url=https://bianet.org/haber/recession-continues-in-turkey-s-largest-lake-283991 |access-date=2023-12-12 |website=[[Bianet]] |language=en}}</ref>