GeoWord of the Day

The GeoWord of the Day is a free service of the American Geosciences Institute. All of the terms and definitions are from the Glossary of Geology, 5th Edition Revised.

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perinium . perine. Pl: perinia. Adj: perinate.

vertical fold . A fold having a vertical axis.

eruption cycle . The sequence of events that occurs during a volcanic eruption; the regular change in the behavior of the eruptions in a period of activity.

Urodela (U-ro-de'-la). An order of caudate lissamphibians that includes salamanders and newts. Range, Upper Jurassic to Holocene.

convection [tect] . A process of heat transfer involving movement of mass. During convection, warmer, less dense material rises while cooler, denser material sinks. Convection takes place when buoyancy forces exceed the strength of the material, and heat flow is too great to be accommodated by conduction. Convection occurs in the Earth's mantle beneath the lithosphere; it is not clear whether whole-mantle convection occurs, or whether upper-mantle convection is independent of lower-mantle convection. Convective flow may exert shear stress to the base of plates and thus may affect plate velocity, but shear due to convection is probably not the main cause of plate motion. Cf: advection [tect].

exopod (ex'-o-pod). The lateral or external ramus of a limb of a crustacean, arising from the basis. Cf: endopod.

hub . The cylindrical or hemispherical projection on the central part (and usually on the lower surface) of a wheel of a holothurian.

stereoplasm (ster'-e-o-plasm''). Gelated protoplasm; specif. the relatively solid axis of granular-reticulose pseudopodia in foraminifers, surrounded by a granular fluid outer portion (rheoplasm). It is noted in foraminifers Peneroplis and Elphidium, but is not visible in most agglutinated types (TIP, 1964, pt.C, p.64).

environmental assessment (en-vi''-ron-men'-tal). A detailed statement prepared by an organization for its own use to appraise the effect of a proposed project on the aggregate of social and physical conditions that influence a community or ecosystem. The assessment is often prepared to determine the need for a formal environmental impact statement.

ghyll . Obsolescent spelling of gill.