Diapir

A mass of buoyant, deformable rock or sediment that rises through denser overlying material, often forming a dome or column. Its movement can fold, fracture, and displace surrounding layers.

Buoyancy: The upward force on an object immersed in a fluid, caused by pressure increasing with depth. A density difference supplies the upward drive for many diapirs.
Density: Mass per unit volume, a physical property that helps determine how materials respond to gravity. A diapir commonly rises because its material is less dense than its surroundings.
Petroleum geology: The study of how petroleum forms, migrates, accumulates, and can be discovered in rocks. Diapirs can create traps for hydrocarbons and complicate their exploration.
Igneous intrusion: A body of magma emplaced within pre-existing rock before solidifying. Magma intrusions rise and occupy space, but are emplaced as molten rock rather than deformable diapiric material.
Viscous flow: Continuous deformation in which material flows under stress and resists motion according to its viscosity. Salt and hot rock can deform viscously as they rise through stronger layers.
Viscosity: A measure of a material's resistance to flowing deformation. Low effective viscosity allows diapiric material to change shape and ascend.
Hydrocarbon trap: A subsurface arrangement of rocks that prevents migrating hydrocarbons from escaping. Folding and faulting around diapirs can create structural traps.
Laccolith: A lens-shaped igneous intrusion that domes overlying rock layers. Its dome resembles a diapir, but it forms from injected magma.
Rayleigh–Taylor instability: An instability that develops when a denser fluid or deformable material overlies a less dense one under gravity. It explains why a buoyant layer can develop rising fingers and descending structures.
Ductile deformation: Permanent change in a material's shape without macroscopic fracture. Diapiric material must deform as it moves through enclosing layers.

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