Salt domes
I don’t know if this is common knowledge.
Basically, underground in the deep of the Earth crust there is often a layer of salt rock, formed when salted water basins evaporated multiple times and get buried by sediments, slowly sinking into the crust due to tectonic activity.
Well, since salt rock has a much lower density than the surrounding rocks, it behaves exactly as a liquid. All around the globe, from the salt layer, immense bubbles and columns of salt called diapirs slowly move upwards, much like magma does, passing through layers of rock and bending them.
Where the bended layers touch the salt diapir some cavities form, making place to petroleum and natural gas to concentrate. On the surface, the bending of the rock layers is detectable through formations like hills but also depressions, created by the subsiding of the hill or by corrosion action by elements.
Where salt domes are found, humans open salt mines and build drilling plants to extract the underground hydrocarbons.

Please note that salt domes are a lot, like if the underground salt basins around the world “boiled” through the crust. If you look up the Zagro mountains in Iran and look at the southernmost part, you can easily spot from the satellite dozens of circular hills all of similar size, some of all even show so-called salt glaciers originated by salt coming out from the crust. Those are all salt diapers pushing the crust and creating hills, and even islands in the Persian Gulf

@til@lemmy.world