Rheid

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. Granite has a measured viscosity at standard temperature and pressure of ~4.5 • 10¹⁹ Pa·s [cite journal
last = Kumagai
first = Naoichi
coauthors = Sadao Sasajima, Hidebumi Ito
title = Long-term Creep of Rocks: Results with Large Specimens Obtained in about 20 Years and Those with Small Specimens in about 3 Years
journal = Journal of the Society of Materials Science (Japan)
volume = 27
issue = 293
pages = 157–161
publisher = Japan Energy Society
url = http://translate.google.com/translate?hl=en&sl=ja&u=http://ci.nii.ac.jp/naid/110002299397/&sa=X&oi=translate&resnum=4&ct=result&prev=/search%3Fq%3DIto%2BHidebumi%26hl%3Den
date = 15 February 1978
accessdate = 2008-06-16] so it should be considered 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.

ee also

*Rheology
*Viscoelasticity

References