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). ...

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 ...

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 An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographic ...

, 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 = , map_image = , location = , country = , country1 = , ...

, such as the

Bas Saharan Basin The Bas Saharan Basin () is an artesian aquifer system which covers most of the Algerian and Tunisian Sahara and extends to Libya, enclosing the whole of the Grand Erg Oriental The Grand Erg Oriental (English: 'Great Eastern Sand Sea') is a large ...

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 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 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 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 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 narro ...

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

References

{{reflist Lakes Salt flats

Water sources

Sahara Sea

Analogue to Martian landforms

List of major chotts

See also

References