In
geology
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
, a chott, shott, or shatt (; ar, شط, šaṭṭ, lit=bank, coast) 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 litre). ...
in
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
's
Maghreb
The Maghreb (; ar, الْمَغْرِب, al-Maghrib, lit=the west), also known as the Arab Maghreb ( ar, المغرب العربي) and Northwest Africa, is the western part of North Africa and the Arab world. The region includes Algeria, ...
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
The capillary fringe is the subsurface layer in which groundwater seeps up from a water table by capillary action to fill pores. Pores at the base of the capillary fringe are filled with water due to tension saturation. This saturated portion of t ...
, 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 soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
sources in the
Sahara
, photo = Sahara real color.jpg
, photo_caption = The Sahara taken by Apollo 17 astronauts, 1972
, map =
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, 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 high
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
, 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 ocea ...
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
The Sahara Sea was the name of a hypothetical macro-engineering project which proposed flooding endorheic basins in the Sahara Desert with waters from the Atlantic Ocean or Mediterranean Sea. The goal of this unrealized project was to create an ...
") 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 planet
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
. 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. It became the most popular celestial object in fiction in the late 1800s as the Moon was evidently lifeless. At the time, the pred ...
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 el Djerid ( ar, شط الجريد ') also spelled ''Sciott Gerid'' and ''Shott el Jerid'', is a chott, a large endorheic salt lake in southern Tunisia. The name can be translated from the Arabic into English as "Lagoon of the Land of Palms" ...
*
Chott ech Chergui
*
Chott Melrhir
Chott Melrhir () also known as Chott Melghir or Chott Melhir is an endorheic chott-kind of salt lake in northeastern Algeria. It is the westernmost part of a series of depressions, which extend from the Gulf of Gabès into the Sahara. They were ...
*
Chott el Fejej
Chott el Fejej, also known as Chott el Fedjedj and Chott el Fejaj, is a long, narrow inlet of the endorheic salt lake Chott el Djerid in southern Tunisia.
History and geography
The bottom of Chott el Fejej lies below sea level and runs in a narr ...
*
Chott el Hodna
The ''Chott el Hodna'' ( ar, شط الحضنة) is a very shallow saline lake in Algeria. It is located within an endorheic basin in the Hodna region, towards the eastern end of the ''Hautes Plaines''. The ''Chott el Hodna'' includes seasonal brac ...
*
Shatt al Gharsah
Shatt al Gharsah, Chott el Gharsa (Arabic language شط الغرسة) is sedimentary basin and also intermittent salt lake in Tunisia
)
, image_map = Tunisia location (orthographic projection).svg
, map_caption = Locat ...
See also
*
Djerid
el-Djerid, also al-Jarīd, ( ar, الجريد; Derja: ''Jerīd''; ) or more precisely the South Western Tunisia Region is a semi-desert natural region comprising three southern Tunisian Governorates, Gafsa, Kebili and Tozeur with adjacent parts ...
*
Sabkha
A sabkha ( ar, سبخة) is a coastal, supratidal mudflat or sandflat in which evaporite-saline minerals accumulate as the result of semiarid to arid climate. Sabkhas are gradational between land and intertidal zone within restricted coastal p ...
*
Shatt al-Arab
The Shatt al-Arab ( ar, شط العرب, lit=River of the Arabs; fa, اروندرود, Arvand Rud, lit=Swift River) is a river of some in length that is formed at the confluence of the Euphrates and Tigris rivers in the town of al-Qurnah in ...
*
Nouakchott
, image_skyline = Nouakchott.jpg
, image_caption = City view of Nouakchott
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References
{{reflist
Lakes
Salt flats