How does a salt pillow develop into a salt dome?

The development of a salt dome from a salt pillow is a process driven by gravitational instability and the plastic flow of salt under pressure.12

When thick salt deposits are buried by denser sedimentary strata, the system becomes gravitationally unstable. Salt begins to flow from its original bed toward a central point, forming a rounded salt pillow. As flow continues into the center of this pillow, the overlying strata are pushed upward, creating a dome-like structure. Simultaneously, the area from which the salt migrated subsides, creating a rim syncline.1

As the salt continues to accumulate, the overlying strata are stretched and fractured by tension. Eventually, the salt pierces through the center of the domed area, transitioning from a pillow into a plug-shaped mass that penetrates the surrounding rock. This upward growth can continue as long as there is a sufficient supply of salt, often keeping pace with the deposition of new sedimentary layers.1