Caspian Depression
Caspian Depression or Pricaspian/Peri-Caspian Depression/Lowland is a low-lying
In physical geography, a lowland is any broad expanse of land with a general low level. The term is thus applied to the landward portion of the upward slope from oceanic depths to continental highlands, to a region of depression in the interior of a mountainous region, to a plain of denudation, or...

Flatland (disambiguation)
Flatland is a 1884 novella written by Edwin Abbott.Flatland may also refer to:* Flatland , a 2007 full-length computer animated film based on the novella...

 region encompassing the northern part of the Caspian Sea
Caspian Sea
The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...

, the largest enclosed body of water
Body of water
A body of water or waterbody is any significant accumulation of water, usually covering the Earth or another planet. The term body of water most often refers to large accumulations of water, such as oceans, seas, and lakes, but it may also include smaller pools of water such as ponds, puddles or...

  on Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. It is the larger northern part of the wider Aral-Caspian Depression
Aral-Caspian Depression
The Aral-Caspian Depression is a lowland depression straddling Europe and Asia around the Aral Sea and Northern Caspian Sea. The most northern part is called the Caspian Depression. The desert part to the east of the Caspian Depression and Caspian is called the Turan Depression...

 around the Aral
Aral Sea
The Aral Sea was a lake that lay between Kazakhstan in the north and Karakalpakstan, an autonomous region of Uzbekistan, in the south...

 and Caspian seas.

The lowest point of the depression is 28m or 92 feet below sea level. The depression
Depression (geology)
A depression in geology is a landform sunken or depressed below the surrounding area. Depressions may be formed by various mechanisms.Structural or tectonic related:...

 lies at the southern end of the Ryn Desert
Ryn Desert
The Ryn Desert or Ryn-Peski Desert , is a desert in western Kazakhstan and southeastern Russia, north of the Caspian Sea and southeast of the Volga Upland. The borders of the desert are very loosely defined. Some maps show the desert almost entirely within the Caspian Depression, stretching almost...

, and is in both Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...

 and Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

. Most of the Russian Republic of Kalmykia
The Republic of Kalmykia is a federal subject of Russia . Population: It is the only Buddhist region in Europe. It has also become well-known as an international chess mecca because its former President, Kirsan Ilyumzhinov, is the head of the International Chess Federation .-Geography:*Area:...

 lies in the Caspian Depression. The Volga River
Volga River
The Volga is the largest river in Europe in terms of length, discharge, and watershed. It flows through central Russia, and is widely viewed as the national river of Russia. Out of the twenty largest cities of Russia, eleven, including the capital Moscow, are situated in the Volga's drainage...

 and the Ural River
Ural River
The Ural or Jayıq/Zhayyq , known as Yaik before 1775, is a river flowing through Russia and Kazakhstan. It arises in the southern Ural Mountains and ends at the Caspian Sea. Its total length is 1,511 mi making it the third longest river in Europe after the Volga and the Danube...

 flow into the Caspian Sea through this region. The deltas of the Ural and Volga Rivers are extensive wetlands.

The North Caspian depression is part of the continental
Continental climate
Continental climate is a climate characterized by important annual variation in temperature due to the lack of significant bodies of water nearby...

 or semi-arid
A semi-arid climate or steppe climate describes climatic regions that receive precipitation below potential evapotranspiration, but not extremely...

 desert biome
Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a...

. The area receives 300 mm (12 in) of rain or less per year, on average, and less than 10% of the region is irrigated. Karagiye
Karagiye is a long karst trench close to the Caspian Sea. At approximately below sea level it is the lowest point both in Kazakhstan and the former USSR...

, the lowest point in Kazakhstan, is in the depression, at 132 metres (433 ft) below sea level.

Much of the Caspian Depression is below sea-level, consisting of large areas of marshlands in the eastern region. It is one of the largest flat lowland areas in Central Asia
Central Asia
Central Asia is a core region of the Asian continent from the Caspian Sea in the west, China in the east, Afghanistan in the south, and Russia in the north...

, covering approximately 200,000 kilometres² (77,220 miles²). The area is very rich in underground oil and gas reserves, and oil and natural gas pipelines cross the depression from north to south and east to west. Many geologists believe the Caspian Sea and the depression were formed by tectonic forces. Some of them also believe that the North Caspian depression became separated from the open ocean in ancient times to form an enormous salt lake. Part of the ancient Silk Road
Silk Road
The Silk Road or Silk Route refers to a historical network of interlinking trade routes across the Afro-Eurasian landmass that connected East, South, and Western Asia with the Mediterranean and European world, as well as parts of North and East Africa...

 ran through this region. The two largest cities in the depression are Astrakhan
Astrakhan is a major city in southern European Russia and the administrative center of Astrakhan Oblast. The city lies on the left bank of the Volga River, close to where it discharges into the Caspian Sea at an altitude of below the sea level. Population:...

 in Russia, and Atyrau
Atyrau , known as Guryev until 1991, is a city in Kazakhstan, and the capital of Atyrau Province. It is located at the mouth of the Ural River, 2700 kilometers west of Almaty and 350 kilometers east of the Russian city of Astrakhan. Other transliterations include Aterau, Atirau, Atyraw, Atyraou,...

 in Kazakhstan. Today, the region is used mainly for livestock raising.

The depression is also noted for salt dome
Salt dome
A salt dome is a type of structural dome formed when a thick bed of evaporite minerals found at depth intrudes vertically into surrounding rock strata, forming a diapir....

s, particularly Volgograd salt, whose sizes increase dramatically as one travels from the Ryn Desert
Ryn Desert
The Ryn Desert or Ryn-Peski Desert , is a desert in western Kazakhstan and southeastern Russia, north of the Caspian Sea and southeast of the Volga Upland. The borders of the desert are very loosely defined. Some maps show the desert almost entirely within the Caspian Depression, stretching almost...

 toward the Caspian Sea. Russian satellite photos have revealed huge deposits of salt domes (about 1,200), in the Caspian Depression in western Kazakhstan. One dome, called the Chelkar Deposit, covers an area of 3,237 kilometres² (1,249 miles²) and is nearly 8 kilometres (5 mi) deep.

The southern region of the depression, or the north coast of the Caspian Sea, is characterized by large development of damp sites resulting from tidal phenomena. The depression is also home to a large number of insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

, with several thousand different species likely living in the region around the Caspian Sea. Studies have shown that water pollution
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....

, mostly coming from the Volga River, poses a serious threat to the biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...

 of the Caspian Depression. Water pollution is contributed mainly by industrial
Industry refers to the production of an economic good or service within an economy.-Industrial sectors:There are four key industrial economic sectors: the primary sector, largely raw material extraction industries such as mining and farming; the secondary sector, involving refining, construction,...

, agricultural, and household discharges.
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