A salt dome is a mound or column of salt that has intruded upwards into overlying sediments. Salt domes can form in a sedimentary basin where a thick layer of salt is overlain by younger sediments of significant thickness. Where conditions allow, salt domes can rise thousands of feet above the layer of salt from which they began growing.The development of salt domes can deform rock units into traps that hold oil and natural gas. They are often mined as sources of salt and sulfur. The impermeable nature of the salt can make them important sites for underground storage or underground disposal of hazardous waste.
Deformation of Salt Under Pressure
Unlike most other types of sediment, salt has the ability to change shape and flow when placed under enough pressure. To develop a salt dome, the pressure on the salt must be high enough to intrude overlying sediments. The pressure must be great enough to overcome several obstacles. These include the weight of overlying strata, the strength of overlying strata, frictional forces, and the force of gravity resisting uplift.
Two sources of pressure that have produced salt domes are the downward pressure of overlying sediment and the lateral pressure of tectonic movement.
If an area of weakness or instability develops in the overlying sediment, salt under adequate pressure can intrude into it. The weakness might be caused by extension fractures, a developing anticline, a thrust fault, or a valley eroded into Earth's surface above.
Once the salt begins to flow, it can continue as long as the pressure on the salt is high enough to overcome the resisting forces. Flow will stop when the salt has risen to a height where equilibrium conditions exist.
Economic Importance of Salt Dome
Salt domes serve as oil and natural gas reservoirs, sources of sulfur, sources of salt, underground storage sites for oil and natural gas, and disposal sites for hazardous waste.
Oil and Natural Gas Reservoirs
Salt domes are very important to the petroleum industry. As a salt dome grows, the cap rock above it is arched upwards. This cap rock can serve as an oil or natural gas reservoir.