Salt dome
Overview
 
A salt dome is a type of structural dome
Dome (geology)
In structural geology, a dome is a deformational feature consisting of symmetrically-dipping anticlines; their general outline on a geologic map is circular or oval...

 formed when a thick bed of evaporite
Evaporite
Evaporite is a name for a water-soluble mineral sediment that result from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporate deposits, marine which can also be described as ocean deposits, and non-marine which are found in standing bodies of...

 minerals (mainly salt, or halite
Halite
Halite , commonly known as rock salt, is the mineral form of sodium chloride . Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on the amount and type of impurities...

) found at depth intrudes vertically into surrounding rock strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

, forming a diapir
Diapir
A diapir is a type of intrusion in which a more mobile and ductily-deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh-Taylor instability-type structures in regions with low tectonic stress...

.

The salt that forms these domes was deposited within restricted marine basins. Due to restricted flow of water into a basin, evaporation occurs resulting in the precipitation of salts from solution, depositing evaporites.
Encyclopedia
A salt dome is a type of structural dome
Dome (geology)
In structural geology, a dome is a deformational feature consisting of symmetrically-dipping anticlines; their general outline on a geologic map is circular or oval...

 formed when a thick bed of evaporite
Evaporite
Evaporite is a name for a water-soluble mineral sediment that result from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporate deposits, marine which can also be described as ocean deposits, and non-marine which are found in standing bodies of...

 minerals (mainly salt, or halite
Halite
Halite , commonly known as rock salt, is the mineral form of sodium chloride . Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on the amount and type of impurities...

) found at depth intrudes vertically into surrounding rock strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

, forming a diapir
Diapir
A diapir is a type of intrusion in which a more mobile and ductily-deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh-Taylor instability-type structures in regions with low tectonic stress...

.

The salt that forms these domes was deposited within restricted marine basins. Due to restricted flow of water into a basin, evaporation occurs resulting in the precipitation of salts from solution, depositing evaporites. It is recognised that a single evaporation event is rarely enough to produce the vast quantities of salt found in evaporite deposits indicating that a sustained period of episodic flooding and evaporation of the basin must occur, as can be seen from the example of the Mediterranean Messinian salinity crisis
Messinian salinity crisis
The Messinian Salinity Crisis, also referred to as the Messinian Event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partly or nearly complete desiccation throughout the latter part of the Messinian age of the Miocene...

. At the present day, evaporite deposits can be seen accumulating in basins that merely have restricted access but do not completely dry out; they provide an analogue to some deposits recognised in the Geological record, such as the Garabogazköl
Garabogazköl
The Garabogazköl Aylagy, alternatively the Kara-Bogaz-Gol is a shallow inundated depression in the northwestern corner of Turkmenistan. It forms a lagoon of the Caspian Sea with a surface area of about...

 basin in Turkmenistan
Turkmenistan
Turkmenistan , formerly also known as Turkmenia is one of the Turkic states in Central Asia. Until 1991, it was a constituent republic of the Soviet Union, the Turkmen Soviet Socialist Republic . Turkmenistan is one of the six independent Turkic states...

.

Over time, the salt is covered with sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

 and becomes buried. Since the density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 of salt is generally less than that of surrounding material, it has a tendency to move upward toward the surface, forming large bulbous domes, diapirs, sheets, pillars and other structures as it rises (see salt tectonics
Salt tectonics
500px|thumb|rightSalt tectonics is concerned with the geometries and processes associated with the presence of significant thicknesses of evaporites containing rock salt within a stratigraphic sequence of rocks...

). If the rising salt diapir breaches the surface, it can become a flowing salt glacier
Salt glacier
A salt glacier is a flow of salt that is created when a rising diapir in a salt dome breaches the surface. Gravity causes the salt to flow like glaciers into adjacent valleys. Most of the flow occurs during the winter, when the salt is wet, as the strength of salt is critically dependent on its...

. In cross section, these large domes may be anywhere from 1 to 10 km (0.621372736649807 to 6.2 ) across, and extend as far down as 6.5 kilometres (4 mi).

Major occurrences of salt domes are found along the Gulf Coast of the USA in Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

 and Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

. One example of an island
Island
An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...

 formed by a salt dome is Avery Island in Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

. At present ocean levels it is no longer surrounded by the sea but it is surrounded by bayou
Bayou
A bayou is an American term for a body of water typically found in flat, low-lying areas, and can refer either to an extremely slow-moving stream or river , or to a marshy lake or wetland. The name "bayou" can also refer to creeks that see level changes due to tides and hold brackish water which...

s on all sides.

Another example of an emergent salt dome is at Onion Creek, Utah / Fisher Towers
Fisher Towers
Fisher Towers are a series of towers made of Cutler sandstone capped with Moenkopi sandstone and caked with a stucco of red mud located near Moab, Utah . The Towers are named for a miner who lived near them in the 1880s. The Tower is world renowned as a subject for photography and for its classic...

 near Moab, Utah, U.S. These two images show a Cretaceous age salt body that has risen as a ridge through several hundred meters of overburden, predominately sandstone. As the salt body rose, the overburden formed an anticline (arching upward along its centerline) which fractured and eroded to expose the salt body.
The term "salt dome" is also sometimes inaccurately used to refer to dome-shaped silo
Silo
A silo is a structure for storing bulk materials.Silo may also refer to:* Silo , a 3D modeling software* Silo , a defunct chain of retail electronics stores* SILO , used in Linux...

s used to store rock salt for melting snow on highways. These domes are actually called monolithic dome
Monolithic dome
A monolithic dome is a structure cast in a one-piece form. The form may be permanent or temporary and may or may not remain part of the finished structure....

s and are used to store a variety of bulk goods.

Commercial uses

The rock salt that is found in salt domes is mostly impermeable. As the salt moves up towards the surface, it can penetrate and/or bend strata of existing rock with it. As these strata are penetrated, they are generally bent slightly upwards at the point of contact with the dome, and can form pockets where petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

 and natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 can collect between impermeable strata of rock and the salt. The strata immediately above the dome that are not penetrated are pushed upward, creating a dome-like reservoir above the salt where petroleum can also gather. These oil pools can eventually be extracted, and indeed form a major source of the petroleum produced along the coast of the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

.

The caprock above the salt domes is sometimes the site of deposits of native sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

, which is recovered by the Frasch process
Frasch process
The Frasch process is a method to extract sulfur from underground deposits. It is the only economic method of recovering sulfur from elemental deposits...

.

Other uses include storing oil
Strategic Petroleum Reserve
The Strategic Petroleum Reserve is an emergency fuel storage of oil maintained by the United States Department of Energy.- United States :The US SPR is the largest emergency supply in the world with the current capacity to hold up to ....

, natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

, hydrogen gas, or even hazardous waste
Waste Isolation Pilot Plant
The Waste Isolation Pilot Plant, or WIPP, is the world's third deep geological repository licensed to permanently dispose of transuranic radioactive waste for 10,000 years that is left from the research and production of nuclear weapons...

 in large caverns
Cave
A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like rock shelters, sea caves, and grottos.Speleology is the science of exploration and study...

 formed after salt mining, as well as excavating the domes themselves for uses in everything from table salt
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

 to the granular material used to prevent roadways from icing over.

See also

  • Plasticity (physics)
    Plasticity (physics)
    In physics and materials science, plasticity describes the deformation of a material undergoing non-reversible changes of shape in response to applied forces. For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the...

  • Salt tectonics
    Salt tectonics
    500px|thumb|rightSalt tectonics is concerned with the geometries and processes associated with the presence of significant thicknesses of evaporites containing rock salt within a stratigraphic sequence of rocks...

  • Strategic Petroleum Reserve
    Strategic Petroleum Reserve
    The Strategic Petroleum Reserve is an emergency fuel storage of oil maintained by the United States Department of Energy.- United States :The US SPR is the largest emergency supply in the world with the current capacity to hold up to ....

  • Underground hydrogen storage
    Underground hydrogen storage
    Underground hydrogen storage is the practice of hydrogen storage in underground caverns, salt domes and depleted oil/gas fields. Large quantities of gaseous hydrogen have been stored in underground caverns by ICI for many years without any difficulties...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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