An endorheic basin (from Greek endo ‘inside’ + rhein ‘to flow’; also terminal or closed basin) is a closed drainage basin that retains water and allows no outflow to other bodies of water such as rivers or oceans. Normally the water accruing in drainage basins flows out through surface rivers or by underground diffusion through permeable rock to the oceans. However, in an endorheic basin, rain (or other precipitation) that falls within it does not flow out but may only leave the drainage system by evaporation and seepage. Endorheic basins are also called internal drainage systems.

Endorheic regions, in contrast to exorheic regions which flow to the ocean in geologically defined patterns, are closed hydroloic systems. Their surface waters drain to inland terminal locations where the water evaporates or seeps into the ground, having no access to discharge into the sea. Endorheic water bodies include some of the largest lakes in the world, such the Aral Sea and the Caspian Sea, the world’s largest saline body of water cut off from the ocean.

Endorheic lakes

Endorheic lakes are bodies of water that do not flow into the sea. Most of the water falling on earth masses finds its way to the oceans through a network of rivers, lakes and wetlands or through evaporation. However, there is a class of water bodies that are located in closed or endorheic watersheds where the topography prevents their drainage to the oceans. These endorheic watersheds (containing water in rivers or lakes that form a balance of surface inflows, evaporation and seepage) are often called terminal lakes or sink lakes.

Endorheic lakes are usually in the interior of a body mass, far from an ocean. Their watersheds often confined by natural geologic land formations such as a mountain range, cutting off water access to the ocean. The inland water flow into dry watersheds where the water evaporates, leaving a high concentration of minerals and other inflow erosion products. Over time this imput of erosion products can cause the endorheic lake to become relatively saline. Since the main outflow pathways of these lakes are chiefly through evaporation and seepage, endorheic lakes are usually more sensitive to environmental pollutants inputs than water bodies that have access to oceans.

Occurrence

Endorheic regions can occur in any climate but are most commonly found in hot desert locations. In areas where rainfall is higher, riparian erosion will generally carve drainage channels (particularly in times of flood), breaking the enclosed endorheic hydrological system’s geographical barrier and opening it to the surrounding terrain. The Black Sea was likely such a lake, having once been an independent hydrological system before the Mediterranean Sea broke through the terrain separating the two.

Endorheic regions tend to be far inland with their boundaries defined by mountains or other geological features that sever their access to oceans. Since the inflowing water can evacuate only through seepage or evaporation, dried minerals or other products collect in the basin, eventually making the water saline and also making the basin vulnerable to pollution. Continents vary in their concentration of endorheic regions due to conditions of geography and climate. Australia has the highest percentage of endorheic regions at 18 percent while North America has the least at 5 percent. Approximately 18 percent of the earth’s land drains to endorheic lakes or seas, the largest of these land areas being the interior of Asia.

In hot deserts, water inflow is low and loss to solar evaporation high, drastically reducing the formation of complete drainage systems. Closed water flow areas often lead to the concentration of salts and other minerals in the basin. Minerals leached from the surrounding rocks are deposited in the basin, and left behind when the water evaporates. Thus endorheic basins often contain extensive salt pans (also called salt flats, salt lakes, alkali flats or playas). These areas tend to be large, flat hardened surfaces and are sometimes used for aviation runways or land speed record attempts.

Both permanent and seasonal endorheic lakes can form in endorheic basins. Some endorheic basins are essentially stable, climate change having reduced precipitation to the degree that a lake no longer forms. Even most permanent endorheic lakes change size and shape dramatically over time, often becoming much smaller or breaking into several smaller parts during the dry season. As humans have expanded into previously uninhabitable desert areas, the river systems that feed many endorheic lakes have been altered by the construction of dams and aqueducts. As a result many endorheic lakes in developed or developing countries have contracted dramatically, resulting in increased salinity, higher concentrations of pollutants, and the disruption ecosystems.

Notable endorheic basins and lakes

One of the few endorheic lakes in a cold desert location, Antarctica’s Lake Vida remains liquid because its salinity is seven times that of seawater.

Asia

Much of western and Central Asia is a single, giant inland basin. It contains a number of lakes, including:

• The Central Asian Internal Drainage Basin, the largest of the three major basins covering Mongolia.
• The Caspian Sea, the largest lake on Earth. In fact, a large part of Eastern Europe drained by the Volga River also belongs to its basin.
• The Aral Sea, whose tributary rivers have been diverted, leading to a dramatic shrinkage of the lake. The resulting ecological disaster has brought the plight faced by internal drainage basins to public attention.
• Lake Balkhash (Kazakhstan)
• Lop Nur Basin, in the southeastern portion of Xinjiang Uygur Autonomous Region in northwestern China
• Issyk-Kul, Son-Kul and Chatyr-Kul lakes in Kyrgyzstan
• Sistan Basin covering areas of Iran and Afghanistan
• Tarim Basin in Xinjiang Uyghur Autonomous Region
• Uvs Nuur basin, Mongolia, Tuvan Republic of Russia
• The Dead Sea, the lowest surface point on Earth and one of its saltiest bodies of water, lies between Israel and Jordan.
• Sambhar Lake in Rajasthan, north-western India, is also the terminal point of an endorheic basin.

Australia

Australia, being very dry and having exceedingly low runoff ratios due to its ancient soils, has a great prominence of variable, endorheic drainages. The most important are:

• Lake Eyre Basin, which drains into the highly variable Lake Eyre and includes Lake Frome.
• Lake Torrens, to the west of the Flinders Ranges in South Australia.
• Lake Corangamite, a highly saline crater lake in western Victoria.
• Lake George, formerly connected to the Murray-Darling Basin

Africa

• Lake Turkana in Kenya
• The Okavango Delta, an endorheic inland delta in the Kalahari Desert of Botswana
• Lake Ngami in Botswana
• Lake Chad (between Chad and Cameroon), fed by the Chari and Logon rivers
• Etosha pan in Namibia’s Etosha National Park
• Qattara Depression in Egypt
• Chott Melrhir in Algeria
• Lake Chilwa in Malawi
• Afar Depression in Eritrea, Ethiopia and Djibouti

North America

• The Valley of Mexico. In Pre-Columbian times, the Valley was substantially covered with five lakes, including Lake Texcoco, Lake Xochimilco, and Lake Chalco.
• Crater Lake in Oregon
• Devil's Lake (North Dakota)
• Devil's Lake (Wisconsin)
• The Great Divide Basin in Wyoming, a small endorheic basin that straddles the Continental Divide.
• The United States’ Great Basin, which covers much of Nevada and Utah, includes:
• The Black Rock Desert in Nevada, location of the Thrust2 and ThrustSSC landspeed record runs, and the annual home to the Burning Man festival
• Death Valley in California and Nevada, the lowest land point in the United States
• Groom Dry Lake in Nevada, location of the secret Area 51 base
• Utah’s Great Salt Lake, the largest terminal lake in the Western Hemisphere
• Salton Sea in California, a lake accidentally created in 1905 when irrigation canals ruptured, filling a desert endorheic basin and recreating an ancient saline sea
• Utah’s Sevier Lake
• Pyramid Lake in Nevada
• Mono Lake in California
• Tulare Lake, an endorheic basin at the southern end of the San Joaquin Valley fed by the Kern River; since the late 19th century the lake bed has been reclaimed and used as farmland, though it occasionally floods when rainfall is especially heavy
• New Mexico has a number of desert endorheic basins including:
• The Tularosa Basin, a rift valley;
• Zuni Salt Lake, a maar;
• Bolsón de Mapimí, in northern Mexico;
• Guzmán Basin, in northern Mexico southwestern New Mexico;
• Lago de Atitlán, in the highlands of Guatemala;

Europe

• Neusiedlersee in Austria
• Lake Trasimeno in Italy
• Lake Prespa between Albania, Greece and Macedonia

All these lakes are drained however either through manmade canals or via karstic phenomena. Minor additional endorheic lakes exist throughout the Mediterranean countries Spain (e.g. Laguna de Gallocanta), Italy, Cyprus (Larnaca and Akrotiri salt lakes) and Greece.

South America

• Altiplano basin, one of the largest and second highest in the world.
• Lake Valencia (Spanish: Lago de Valencia) the second largest lake in Venezuela.
• Salar de Atacama, Atacama Desert, Chile (although close to the Altiplano it is not part of it)
• Northwest Pampas Basins in the Dry Pampas of Argentina
• Southwest Pampas Basins in the Dry Pampas of Argentina
• Meseta Somuncura in the Patagonia region of Argentina

Ancient

Some of the Earth’s ancient endorheic systems include:

• The Black Sea, until its merger with the Mediterranean
• The Mediterranean Sea itself and all its tributary basins, during its Messinian desiccation (5 m.y. BP aprox.) as it became disconnected from the Atlantic Ocean.
• Lake Lahontan in the western US
• Ebro and Duero basins, draining most of northern Spain during the Neogene and perhaps Pliocene.
• Lake Bonneville (Utah)

See also

• List of endorheic basins

References

External links

• Primer on endorheic lakes
• The Silk Roads and Eurasian Geography
• The role of climate during high plateau formation. Insights from numerical experiments