Van Lake
Van Lake is the largest lake in Turkey, located in the far
east of the country. It is a saline and 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). The original
outlet from the basin was blocked by an ancient volcanic
eruption.
Hydrology and chemistry
Lake Van is 119 km 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
(5,381 ft) above sea level and the shore length is 430
kilometres (267 mi). Lake Van has an area of 3,755 km²
(1,450 sq mi) and a volume of 607 cubic kilometers (145.6 cu
mi).
The western portion of the lake is deepest, with a large
basin deeper than 400 m (1,312 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 (164 ft), with a maximum
depth of about 150 m (492 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.
Geology
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, 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 (72m above the current height) had been during the
last ice age, about 18,000 years ago. About 9,500 years ago
there was a dramatic drop to more than 300m below the
present level. This was followed by an equally dramatic rise
around 6,500 years ago.
Similar but smaller fluctuations have been seen recently.
The level of the lake rose by at least three metres during
the 1990s, drowning much agricultural land, and (after a
brief period of stability and then retreat) seems to be
rising again. The level has risen about two meters in the
ten years immediatey prior to 2004.
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 400m thick in places, and has
attracted climatologists and vulcanologists interested in
drilling cores to examine the layered sediments.
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 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.