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What is a Salt Dome?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

A salt dome is a geologic formation caused by a phenomenon known as diapirism, in which lighter materials force their way up through denser ones. Salts and other evaporated minerals are generally lighter than the sedimentary rock which surrounds them, and as a result, salt has a tendency to well up, creating a visible bulge in the surface of the earth which is often capped with a layer of rock. Salt domes have been utilized by humans for centuries as readily available supplies of salt, since they typically contain a high concentration of halite, otherwise known as table salt.

The formation of a salt dome takes centuries. It starts with the formation of an isolated marine inlet, which slowly evaporates, concentrating the salts. Geologists believe that these inlets must be flooded and evaporated several times to reach the concentration of salt needed to create a salt dome. Once a large deposit of salts is created, sediments are deposited over the salt as the centuries progress, but the salt will continue drifting to the top, because it is less dense than the sediments around it. As a result, the salt creates a distinctive bulge, and it appears to be boring its way through the surrounding rock when viewed in cross-section.

Salt from a salt dome.
Salt from a salt dome.

Salt domes can be found all over the world, in a wide variety of settings. Some are in isolated desert environments, testifying to the fact that these regions were once covered in water, while others are in marshes and swamps near the ocean. Historically, salt domes have been mined for their cargo of salt, and they also have other economic uses which can make ownership or control of a salt dome extremely profitable.

Salt domes can be found in marshes and swamps near the ocean.
Salt domes can be found in marshes and swamps near the ocean.

Many salt domes contain pockets of oil and natural gas, which become trapped as the salt rises. These deposits have nowhere to go until they are drilled, and they can be quite significant. Salt is also an extremely stable storage medium, leading some companies to use salt domes to store deposits of fuel and natural gas; it has been suggested that nuclear waste could potentially be stored in salt domes as well, since salt is inert and very stable.

An incomplete salt dome is known as a salt pillow, and salt domes can turn into salt glaciers, huge deposits of salt which actually move across the surface of the Earth, typically when the ground and the salt are lubricated by rain.

Frequently Asked Questions

What exactly is a salt dome?

Louisiana is home to a number of salt domes.
Louisiana is home to a number of salt domes.

A salt dome is a geological formation created when a thick bed of evaporite minerals, primarily salt (halite), is pushed up by the intense pressure of overlying sediment. This upward movement, known as diapirism, causes the salt to penetrate through the rock layers, forming a dome-like structure that can span several miles in diameter and extend deep into the Earth's crust.

How does a salt dome form?

Salt domes typically contain a high concentration of halite, or table salt.
Salt domes typically contain a high concentration of halite, or table salt.

Salt domes form over millions of years. They begin with the accumulation of salt deposits in a restricted basin, which are then buried by layers of sediment. The lower density and plasticity of the salt compared to the overlying rock cause it to flow upwards, piercing through the sedimentary layers to form a dome-like shape. This process is driven by the buoyancy of the salt under the weight of the overlying sediments.

Where are salt domes commonly found?

Salt domes are commonly found in regions where large quantities of salt were deposited in ancient seas or lakes that have long since evaporated. Notable areas with salt domes include the Gulf Coast of the United States, the North Sea, parts of the Middle East, and the Zagros Mountains in Iran. These structures are often associated with oil and natural gas deposits.

Why are salt domes economically important?

Salt domes are economically significant because they frequently trap oil, natural gas, and sulfur, making them valuable sites for energy resources. According to the U.S. Energy Information Administration, many oil and gas reservoirs are associated with salt dome formations. Additionally, their underground cavities can be used for the storage of hydrocarbons and the disposal of hazardous waste.

Can salt domes pose any risks or hazards?

While salt domes are important for resource extraction, they can pose risks such as land subsidence or sinkholes if the salt is dissolved by groundwater or if their structural integrity is compromised by mining activities. In some cases, the collapse of a salt dome can trigger earthquakes or release stored hydrocarbons, leading to environmental hazards.

Are salt domes related to any unique ecosystems or wildlife?

Salt domes can influence the surrounding ecosystem by creating unique soil conditions that support specialized plant communities. These habitats can be home to distinct wildlife adapted to the saline environment. However, the ecological impact is more localized and does not typically result in large-scale biodiversity hotspots, as the primary interest in salt domes is often related to their geological and economic significance.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

Discussion Comments

Oceana

I thought we got all our salt from reserves under the sea. I didn't know that any were available on land! That's much more convenient for harvesting.

JackWhack

@healthy4life – Yes, they do remove the salt. I read about salt dome storage awhile back, and it does sound like a good idea for gas companies.

They have to inject some water inside the salt dome. This makes the salt dissolve, and they can squirt it out into the middle of the ocean.

I read that storage down there is a lot cheaper than on land. Also, you don't have to worry about anyone trying to steal it! I doubt anyone would have the tools to rob a salt dome of oil or gas!

healthy4life

If you are using a salt dome for gas storage, doesn't the salt first have to be removed? It just seems to me that it would take up too much space.

StarJo

I heard about a salt dome in geology class. There are some under the ocean that have coral beds on top. The ones I heard about are in some sort of national sanctuary, so I believe they are protected.

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    • Salt from a salt dome.
      By: Elena Moiseeva
      Salt from a salt dome.
    • Salt domes can be found in marshes and swamps near the ocean.
      By: Paul Wolf
      Salt domes can be found in marshes and swamps near the ocean.
    • Louisiana is home to a number of salt domes.
      By: qingwa
      Louisiana is home to a number of salt domes.
    • Salt domes typically contain a high concentration of halite, or table salt.
      By: Jiri Hera
      Salt domes typically contain a high concentration of halite, or table salt.