Salt Domes

There are 11 interior salt domes in north Louisiana and not less than 100 salt domes in the coastal area. Salt domes, or plugs, are an important element in the origin of the south Louisiana oil fields. 

Exploration for oil and gas has revealed salt domes in more than 100 sedimentary basins that contain rock salt layers several hundred meters or more thick. Salt domes are known in every ocean and continent. 

Salt domes supply industrial commodities, including fuel, minerals, chemical feedstock, and storage caverns. Giant oil or gas fields are associated with salt domes in many basins around the world, especially in the Middle East, North Sea, and South Atlantic regions. Salt domes are also used to store crude oil, natural gas (methane), liquefied petroleum gas, and radioactive or toxic wastes.

Salt domes are largely subsurface geologic structure that consists of a vertical cylinder of salt embedded in horizontal or inclined strata. In the broadest sense, the term includes both the core of salt and the strata that surround and are “domed” by the core. Major accumulations of oil and natural gas are associated with salt domes in the U.S., Mexico, the North Sea, Germany, and Romania; domes along the Gulf Coast contain large quantities of sulfur. Salt domes are also major sources of salt and potash on the Gulf Coast and in Germany, and they have been used for underground storage of liquefied propane gas. Storage “bottles,” made by drilling into the salt and then forming a cavity by subsequent solution, have been considered as sites for disposal of radioactive wastes.

The salt that forms these deposits was laid down in prehistoric times, mainly in places where inland seas were periodically connected and disconnected from oceans. As these seas are cut off from the main body of water, the water evaporates, leaving immense salt pans. Over time, the salt is covered with sediment and becomes buried. Since the density of salt is generally less than that of surrounding material, it has a tendency to move upward toward the surface, forming large bulbous domes, sheets, pillars and other structures as it rises. If the rising salt diapir breaches the surface, it can become a flowing salt glacier. In cross section, these large domes may be anywhere from 1 to 10 kilometers across and extend as far down as 6.5 kilometers.

One example of an island formed by a salt dome is Avery Island in Louisiana.

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