:''For places in Schleswig-Holstein in Germany, see
Rheide.''
In
geology, a 'rheid' is a
solid material that deforms by
viscous flow. To be considered a rheid, deformation by flow should exceed
elastic deformation by at least a factor of three.
Types of rheids
Almost any type of
rock can behave as a rheid under appropriate conditions of
temperature and
pressure. For example, the
Earth's
mantle is believed to undergo
convection over long time scales. Since the mantle is known to be solid (it supports the propagation of
shear waves), it must be behaving as a rheid.
Halite, the mineral form of
salt, is a geological material that behaves as a rheid over relatively short time periods. As salt is buried by other types of
sediments, it will often flow laterally towards regions of less confining
stress. Through this mechanism,
salt domes and other structures are formed. In some areas, such as the
Gulf of Mexico, these structures often serve as traps for
petroleum and
natural gas.
See also
★
Rheology
★
Viscoelasticity
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