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52-543: The term sabkha has also been used as a general term for any flat area, coastal or interior, where, as the result of evaporation, salt and other evaporite minerals precipitate near or at the surface. The term continental sabkha is used for such environments found within deserts. Because of the confusion created by using sabkha for salt flats and playas , it has been proposed that the usage of this term be abandoned for playas and other intracontinental basins and flats. The origin and progression of coastal sabkha development at

104-489: A salt pan , pan , or salt flat (the latter being a remnant of a salt lake ). Hardpan is the dry terminus of an internally drained basin in a dry climate, a designation typically used in the Great Basin of the western United States. Another term for dry lake bed is playa . The Spanish word playa ( pronounced [ˈplaʝa] ) literally means "beach". Dry lakes are known by this name in some parts of Mexico and

156-408: A playa ( / ˈ p l aɪ - ə / ), is a basin or depression that formerly contained a standing surface water body, which disappears when evaporation processes exceed recharge. If the floor of a dry lake is covered by deposits of alkaline compounds, it is known as an alkali flat. If covered with salt, it is known as a salt flat . If its basin is primarily salt , then a dry lake bed is called

208-444: A 'seed', such as a piece of a shell. Strong intertidal currents wash the 'seeds' around on the seabed, where they accumulate layers of chemically precipitated calcite from the supersaturated water. The oolites are commonly found in large current bedding structures that resemble sand dunes. The size of the oolites reflect the time that they were exposed to the water before they were covered with later sediment. Oolites are often used in

260-658: A decline from 1992 to 2020. Oolite Oolite or oölite (from Ancient Greek ᾠόν (ōión)  'egg stone') is a sedimentary rock formed from ooids , spherical grains composed of concentric layers. Strictly, oolites consist of ooids of diameter 0.25–2 millimetres; rocks composed of ooids larger than 2 mm are called pisolites . The term oolith can refer to oolite or individual ooids. Ooids are most commonly composed of calcium carbonate ( calcite or aragonite ), but can be composed of phosphate, clays, chert , dolomite or iron minerals, including hematite . Dolomitic and chert ooids are most likely

312-673: A dry lake bed for years until conditions are optimum for hatching. Lepidium davisii is another rare species, a perennial plant whose habitat is restricted to playas in southern Idaho and northern Nevada. Far from major rivers or lakes, playas are often the only water available to wildlife in the desert. Antelope and other wildlife gather there after rainstorms to drink. Threats to dry lakes include pollution from concentrated animal feeding operations such as cattle feedlots and dairies. Results are erosion; fertilizer, pesticide and sediment runoff from farms; and overgrazing . A non-native shrub that has been used for rangeland restoration in

364-582: A flat bed of clay, generally encrusted with precipitated salts. These evaporite minerals are a concentration of weathering products such as sodium carbonate, borax, and other salts. In deserts, a dry lake may be found in an area ringed by bajadas . Dry lakes are typically formed in semi- arid to arid regions of the world. The largest concentration of dry lakes (nearly 22,000) is in the southern High Plains of Texas and eastern New Mexico . Most dry lakes are small. However, Salar de Uyuni in Bolivia , near Potosí ,

416-419: A key role in the formation of sabkhas. The phenomenon of groundwater discharging to the surface doesn't always result in visible open water. Instead, the water evaporates upon reaching the surface, leading to the formation of salt deposits. The salt flats of Abu Dhabi are a typical example of this, with the evaporation of water occurring from the capillary fringe - a subsurface layer where groundwater seeps up from

468-837: A lot of surface area, which promotes high bacterial growth. Some exemplar oolitic limestone was formed in England during the Jurassic period, and forms the Cotswold Hills , the Isle of Portland with its famous Portland Stone , and part of the North York Moors . A particular type, Bath Stone , gives the buildings of the World Heritage City of Bath their distinctive appearance. Carboniferous Hunts Bay Oolite lies under much of south Wales . The Miami Rock Ridge of southeastern Florida,

520-402: A number of rare species that occur nowhere else but in the inhospitable environment of seasonally flooded playas. A new species of giant fairy shrimp was found in 2006. Although a large predatory species, it evaded detection because of the murkiness of the playa's water caused by winds and a fine clay load. This shrimp species is able to regenerate using tiny undetectable cysts that can remain in

572-400: A perfect coincidence of events. First, the playa has to fill with water, which must be deep enough to form floating ice during winter, but still shallow enough that the rocks are exposed. When the temperature drops at night, this pond freezes into thin sheets of "windowpane" ice, which then must be thick enough to maintain strength, but thin enough to move freely. Finally, when the sun comes out,

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624-600: A playa in the Black Rock Desert in western Nevada every year. Fangfang Yao et al (2023), at the University of Virginia reported that more than half of the world's large lakes are drying up. They assessed almost 2,000 large lakes using satellite measurements combined with climate and hydrological models. They found that unsustainable human use, changes in rainfall and run-off, sedimentation, and rising temperatures have driven lake levels down globally, with 53% of lakes showing

676-410: A sabkha coastal plain . These coastal plains are very flat, with reliefs between 10–50 cm, and their seaward slope can be as little as 1:1,000. These environments can be found laterally contemporaneous in parallel belts to the coast as well. Coral reefs , barrier islands , and oolite shoals form the barrier with the open shelf. These types of deposits are indicative of higher energy and protect

728-439: A small tidal range (1–2 m) and low wave energy as a result of the limited fetch. High rates of evaporation result in salinities of 45–46 g l along the open-marine coast of Abu Dhabi and up to 89 g l in more-restricted lagoons. The coast of Abu Dhabi is locally protected from open-marine conditions by a number of peninsulas and offshore shoals and islands associated with the east–west trending Great Pearl Bank. Groundwater plays

780-582: A water table - which intersects the surface. This activity has contributed to the creation of an expansive salt flat, covering approximately 36,000 square kilometers. Much of the chemical content in these flats is attributed to groundwater that seeps to the surface. This seepage results in a concentration of these dissolved substances, which is estimated to be about ten times that found in seawater. The arid conditions of such regions are often characterized by sparse or even completely absent vegetation. This lack of plant cover allows aeolian processes to interact with

832-428: A “chicken wire” crystalline structure. Below this are the intertidal deposits typified by laminated, organic-rich muds formed by the microbial mats that grade downward into more bioturbated muds. The subtidal facies show carbonate grainstones and lagoonal muds. These facies sequences, except for the halite that is frequently re-dissolved when wetted, can easily be preserved. Factors enabling preservation include

884-457: Is a dry inland desert in the Gobi region, flooded by ground water from nearby mountains. The climate is one of the main factors in sabkha development. Rainfall in this arid region usually occurs as thunderstorms and averages 4 cm/year. Temperatures can range in excess of 50 °C to as low as 0 °C. Humidity is linked to the wind direction, with humidity as low as 20% in the mornings from off

936-941: Is also found in Indiana in the United States . The town of Oolitic, Indiana , was founded for the trade in limestone and bears its name. Quarries in Oolitic, Bedford , and Bloomington contributed the materials for such U.S. landmarks as the Empire State Building in New York and the Pentagon in Arlington, Virginia . Many of the buildings on the Indiana University campus in Bloomington are built with native oolitic limestone material, and

988-428: Is formed when water from rain or other sources, like intersection with a water table, flows into a dry depression in the landscape, creating a pond or lake. If the total annual evaporation rate exceeds the total annual inflow, the depression will eventually become dry again, forming a dry lake. Salts originally dissolved in the water precipitate out and are left behind, gradually building up over time. A dry lake appears as

1040-600: Is very little water, dunes can form. The Racetrack Playa , located in Death Valley, California , features a geological phenomenon known as " sailing stones " that leave linear "racetrack" imprints as they slowly move across the surface without human or animal intervention. These rocks have been recently filmed in motion by the Scripps Institution of Oceanography at the University of California, San Diego and are due to

1092-594: The Chrissiesmeer area, to the extensive pans of the Northern Cape province. Terms used in Australia include salt pans (where evaporite minerals are present) and clay pans . In Arabic, a salt flat is called a sabkha (also spelled sabkhah , subkha or sebkha ) or shott ( chott ). In Central Asia, a similar "cracked mud" salt flat is known as a takyr . In Iran salt flats are called kavir . A dry lake

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1144-555: The Oman fold and thrust belt can be as narrow as several hundred meters. If the coast has dune fields, then flooding creates many smaller pools between the crests of the dunes. In some parts of the world, these lakes can also form in inland deserts, filled by rain or a rising water table from underground aquifers . For example, large parts of the Empty Quarter in Saudi Arabia and

1196-610: The Permian Basin in Texas, as well as the Jurassic Gulf of Mexico . Modern sabkhas are present in varying form along the coasts of North Africa , Baja California , and at Shark Bay in Australia . Execution of construction and civil engineering works in sabkhas must overcome a number of geotechnical engineering issues. Sabkha soils are often distinguished by their low strength, as

1248-461: The phreatic surface to form unique landforms, such as sabkhas. Due to the minimal vegetation, aeolian activity has the capacity to cause deep erosion into the surface sediments. However, it's unable to displace material below the capillary zone due to the full saturation of this zone preventing its uplift by the wind. As a result, the Earth’s surface in such regions tends to mimic the shape and slope of

1300-492: The Plain formed the bed of Lake Idaho . Wave action in the lake washed sediments back and forth in the shallows on the southwestern shore, forming ooids and depositing them on steeper benches near the shore in 2- to 40-foot thicknesses. When the lake drained (2 to 4 million years ago), the oolite was left behind, along with siltstone , volcanic tuffs and alluvium from adjacent mountain slopes. The other sediments eroded away, while

1352-422: The concentrated salt solutions found in sabkha brines can weaken the soil structure. In addition, the extreme climatic conditions under which sabkha deposits form - such as substantial temperature fluctuations and recurrent cycles of wetting and drying - can induce instability in these soils, and some minerals that act as binding agents, or 'cements', in these soils have a high solubility, which can potentially reduce

1404-492: The continental sabkha fill with shallow layers of water, and cannot be crossed until they dry out to form a new crust. When the ground is partly dried, a salt crust forms over soft mud or hollow cavities, and a vehicle will become stuck after breaking through the crust. Here are two current examples of dune fields being flooded. The first is not a desert, but a coastal dune field in the Amazon region, flooded by heavy rains. The second

1456-497: The dry interior and building in the afternoon as a strong, onshore wind prevail. At night, relative humidity of 100% can lead to dense fogs. Water temperatures vary by depth with shallow water as much as 10 °C warmer. These high temperatures drive high rates of evaporation in the Persian Gulf , as much as 124 cm/year leading salinity to increase in the shallow lagoons to as much as 70 ppt. The net rate of evaporation from

1508-456: The features silt up, or the land rises, or the sea level falls, then the trapped water evaporates , leaving a flat salt pan, or sabkha . If the coastal region has irregular topography , then the flooding creates large independent creeks, or khors. A khor is a shallow, subtidal flat or tidal inlet. The inlet may host grey mangroves , depending on whether less saline water is available from wadis or groundwater . As sediment begins to accumulate,

1560-678: The ground level. Notably, the sodium chloride concentration can be substantial enough to pose a risk of corrosion . Conversely, the mineral composition within inland sabkhas tends to be more variable when compared to their coastal counterparts. The precipitated minerals within the soil of these inland sabkhas depend significantly on the specific composition of the local groundwater. Thus, the geological and chemical composition of these environments may differ widely based on regional groundwater characteristics. Techniques used to improve sabkha soils for construction purposes include dynamic compaction . Dry lake A dry lake bed , also known as

1612-470: The home aquarium industry because their small grain size (0.2 to 1.22 mm) is ideal for shallow static beds and bottom covering of up to 1" in depth. Also known as "oolitic" sand, the sugar-sized round grains of this sand pass easily through the gills of gobies and other sand-sifting organisms. This unusually smooth sand promotes the growth of bacteria, which are important biofilters in home aquaria. Because of its extremely small grain size, oolitic sand has

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1664-524: The ice melts and cracks into floating panels; these are blown across the playa by light winds, propelling the rocks in front of them. The stones only move once every two or three years and most tracks last for three or four years. While a dry lake bed is itself typically devoid of vegetation, they are commonly ringed by shadscale , saltbrush and other salt-tolerant plants that provide critical winter fodder for livestock and other herbivores . In southwest Idaho and parts of Nevada and Utah there are

1716-720: The islands of the Lower Florida Keys , and much of the Everglades , are underlain by Miami Oolite . This limestone was formed by deposition when shallow seas covered the area between periods of glaciation . The material consolidated and eroded during later exposure above the ocean surface. One of the world's largest freshwater lakebed oolites is the Shoofly Oolite, a section of the Glenns Ferry Formation on southwestern Idaho 's Snake River Plain . 10 million years ago,

1768-404: The khor-lagoon environments, allowing for the growth of mangrove swamps and algal and cyano-bacterial mats that prefer the more closed, lower energy environment. Inland of this are the supratidal sabkhas. The sabkhas can be as wide as 15 km when seaward of dune fields supplying large amounts of sediment. Sabkhas seaward of low outcrops of Miocene carbonate-evaporites or alluvial fans off

1820-429: The khors become more shallow and form a lagoon , or intertidal flat. The lagoons continue to fill until the lagoon floor is exposed at low tide, and the sabkha begins to form. A sabkha may be inundated during higher than normal spring tides, after rainstorms, or when driving winds push seawater onshore to a depth of a few centimeters. Mature sabkhas are only flooded after heavy rainstorms and may eventually coalesce to form

1872-422: The largest salt flat in the world, comprises 4,085 square miles (10,582 square km). Many dry lakes contain shallow water during the rainy season, especially during wet years. If the layer of water is thin and is moved around the dry lake bed by wind, an exceedingly hard and smooth surface may develop. Thicker layers of water may result in a "cracked-mud" surface and teepee structure desiccation features. If there

1924-555: The microbial mats and mangrove paleosoils , found in the sabkha sequence, that have total organic carbon up to 8.2% and hydrogen indices typical of marine type II kerogens . Some ancient analogs include immediate subsurface formations such as the Permian Khuff Formation , Jurassic Arab and Hith anhydrites , and Tertiary sedimentary rocks. Similar deposits are also found in the Ordovician Williston Basin ,

1976-510: The more resistant oolite weathered into hummocks, small arches and other natural "sculptures". The Shoofly Oolite lies on public land west of Bruneau, Idaho managed by the Bureau of Land Management (BLM). The physical and chemical properties of the Shoofly Oolite are the setting for a suite of rare plants, which the BLM protects through land use management and on-site interpretation. This type of limestone

2028-426: The northwest "shamal” gale-force winds that create waves of greater height than the intertidal height and drive water as much as 5 km inland over the sabkha to a depth of a few centimeters. The climate variations lead to the very dynamic nature of a sabkha. Halite is deposited on the surface of the sabkha and gypsum and aragonite precipitate in the subsurface via capillary action from brines brought up from

2080-457: The overall structural integrity. Coastal sabkhas are composed predominantly of minerals such as calcite , dolomite , and gypsum . These are accompanied by smaller quantities of anhydrite , magnesite , halite , and carnalite , as well as various other sulfates and chlorides. The groundwater in these areas is characterized by its high salinity, with sodium chloride levels potentially reaching up to 23%. This saline water often resides close to

2132-507: The progradation of the sabkha with sedimentation rates of 1 m/1000 years and the creation of Stokes surfaces. These surfaces are created by the deflation of the sabkha surface that is related to the level of the groundwater table acting as a local base level. Sabkha deposits are believed to form some of the major subsurface hydrocarbon reservoirs in the Middle East (and elsewhere). The source of these hydrocarbons (both gas and oil) may be

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2184-399: The result of the replacement of the original texture in limestone. Oolitic hematite occurs at Red Mountain near Birmingham, Alabama , along with oolitic limestone. They are usually formed in warm, supersaturated, shallow, highly agitated marine water intertidal environments, though some are formed in inland lakes. The mechanism of formation starts with a small fragment of sediment acting as

2236-442: The sabkha can be as much as an order of magnitude less and has averaged 6 cm for the last 4,000 to 5,000 years. The reasons for this are that the sabkha surface is not a free-water surface, the high humidity during the night, and vertical stratification of the air column. Despite the loss of water due to evaporation, the groundwater, never deeper than 1.5 m, flows seawards and is recharged by continental waters, rainstorms, and

2288-952: The smoothness of the surface allows low-clearance vehicles to travel very fast without any risk of disruption by surface irregularities, and the path traveled has no obstacles to avoid. The dry lake beds at Bonneville Salt Flats in Utah and Black Rock Desert in Nevada have both been used for setting land speed records. Lake Eyre and Lake Gairdner in South Australia have also been used for various land speed record attempts. Dry lake beds that rarely fill with water are sometimes used as locations for air bases for similar reasons. Examples include Groom Lake at Area 51 in Nevada and Edwards Air Force Base (known initially as Muroc Dry Lake) in California. Brines from

2340-476: The southern UAE consist of patterns of high drifting barchan dunes alternating with continental sabkha filled with salt flats. In some places, the continental sabkha connect to form long accessible corridors into the desert. The third picture shows the area south of the crescent-shaped Liwa Oasis in the southern UAE . The picture is about 80 km wide, with each continental sabkha about 2-3 km long and 1 km wide. You can see white deposits of salt covering

2392-456: The southern shore of the Persian Gulf was first discussed in detail in the seminal paper by Evans et al. 1969. The southern shoreline of the Persian Gulf is a shallow, low-angle carbonate ramp characterised by an evaporitic supratidal system passing offshore, via a broad carbonate–evaporite intertidal environment, into a carbonate-dominated subtidal system. This is a low-energy setting with

2444-503: The subsurface of dry lakes are often exploited for valuable minerals in solution. See, for example, Searles Dry Lake and Lithium resources . Under United States law, a "playa lake" may be considered isolated wetlands and may be eligible to enroll in the new wetlands component of the Conservation Reserve Program , enacted in the 2002 farm bill (P.L. 107–171, Sec. 2101). The Burning Man yearly event takes place in

2496-473: The surface of the continental sabkha. The Moreeb Dune , rising 120 m above the continental sabkha, is located roughly in the middle of the picture. The border between Saudi Arabia and the UAE is shown in red. The floor of a continental sabkha is usually a hard-packed combination of sand, mud and salt. It is easy to walk or drive 4x4 vehicles across the dry, continental sabkha. However, after rains and flash-floods,

2548-403: The underlying water table. The resultant surfaces evolve into vast, flat, discharge areas where the process of evaporation leads to the accumulation of salts. Over time, these accumulations form crusts of a salty nature, characterizing the unique landscape of these regions. In the khor-lagoon-sabkha model, an initial rise in sea-level floods coastal areas and creates shallow water features. If

2600-436: The water table. In drier parts of the sabkha the gypsum can be altered to anhydrite and the aragonite can be dolomitized diagenetically . Thermal contraction at night and expansion during the day leads to concave polygonal pans as the edges have been upturned, in part due to growth of evaporites wedging the crack apart. Below this is a gypsum mush where nodules of anhydrite and other sulfates may develop. These might also form

2652-424: The west, Kochia prostrata , also poses a significant threat to playas and their associated rare species, as it capable of crowding out native vegetation and draining a playa's standing water because of its root growth. The extremely flat, smooth, and hard surfaces of dry lake beds make them ideal for fast motor vehicles and motorcycles. Large-sized dry lakes are excellent spots for pursuing land speed records , as

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2704-591: The western United States. This term is used e.g. on the Llano Estacado and other parts of the Southern High Plains and is commonly used to address paleolake sediments in the Sahara like Lake Ptolemy . In South America, the usual term for a dry lake bed is salar or salina , Spanish for salt pan . Pan is the term used in most of South Africa. These may include the small round highveld pans, typical of

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