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In geology
Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...
, a chott, shott, or shatt (; ) is a salt lake
A salt lake or saline lake is a landlocked body of water that has a concentration of salts (typically sodium chloride) and other dissolved minerals significantly higher than most lakes (often defined as at least three grams of salt per liter). I ...
in Africa
Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...
's Maghreb
The Maghreb (; ), also known as the Arab Maghreb () and Northwest Africa, is the western part of the Arab world. The region comprises western and central North Africa, including Algeria, Libya, Mauritania, Morocco, and Tunisia. The Maghreb al ...
that stays dry for much of the year but receives some water in the winter. The elevation of a chott surface is controlled by the position of the water table and capillary fringe, with sediment deflation occurring when the water table falls and sediment accumulation occurring when the water table rises.Swezey, C.S., 2003, The role of climate in the creation and destruction of continental
stratigraphic records: An example from the northern margin of the Sahara Desert, in Cecil, C.B., and Edgar, N.T., eds., Climate Controls on Stratigraphy: SEPM (Society for Sedimentary Geology) Special Publication 77, p. 207-225.
They are formed—within variable shores—by the spring thaw from the Atlas mountain range, along with occasional rainwater or groundwater
Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...
sources in the Sahara
The Sahara (, ) is a desert spanning across North Africa. With an area of , it is the largest hot desert in the world and the list of deserts by area, third-largest desert overall, smaller only than the deserts of Antarctica and the northern Ar ...
, such as the Bas Saharan Basin.
Water sources
The chotts of the Sahara are fed intermittently during periods of infrequent rainfall. They are subject to a high evaporation rate, hence salts eventually accumulate in the surface of the sediment. In fact, annual evaporation rates per year in chotts often exceed 20 times the annual precipitation rate. This salt accumulation can lead chotts to have particularly highalbedo
Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...
, albeit with comparable variability as well. While evaporite
An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...
deposition predominates on chotts, in more humid climatic periods, layers of mud can be deposited on the chott surface. When near a source of loose sand, aeolian deposition can also play a role in the sedimentary deposition on the chott surface.
Sahara Sea
As many lie below sea level, the chotts of the Sahara were viewed by some European colonialists and engineers as an opportunity to create an inland sea in the Sahara Desert (known by many as the " Sahara Sea") by cutting a canal to the Mediterranean Sea (or in some cases, the Atlantic Ocean). Such a channel would allow water from the sea to flow inland. The hope was that this would facilitate trade and naval warfare, as well as change the climatic conditions of the Sahara.Analogue to Martian landforms
Chotts have also been studied because they are believed to be an Earth analogue to similar features on the planetMars
Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...
. Although there are considerable differences between terrestrial and Martian
Mars, the fourth planet from the Sun, has appeared as a setting in works of fiction since at least the mid-1600s. Trends in the planet's portrayal have largely been influenced by advances in planetary science. It became the most popular celes ...
geology, some features on Mars are also believed to be evaporite basins, and consequently share at least some features of chotts. One example of a suspected Martian evaporite basin is Holden Crater.
List of major chotts
* Chott el Djerid * Chott ech Chergui * Chott Melrhir * Chott el Fejej * Chott el Hodna * Shatt al GharsahSee also
* Djerid *Sabkha
A sabkha () is a predominately coastal, supratidal mudflat or sandflat in which evaporite-saline minerals accumulate as the result of a semiarid to arid climate. Sabkhas are gradational between land and intertidal zone within restricted coast ...
*Shatt al-Arab
The Shatt al-Arab () is a river about in length that is formed at the confluence of the Euphrates and Tigris rivers in the town of al-Qurnah in the Basra Governorate of southern Iraq. The southern end of the river constitutes the Iran– ...
*Nouakchott
Nouakchott ( ) is the capital and largest city of Mauritania. Located in the southwestern part of the country, it is one of the largest cities in the Sahara. The city also serves as the administrative and economic center of Mauritania.
Once a ...
References
{{reflist Lakes Salt flats