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Continental volcanic arc Mountains formed in part by igneous activity associated with
the subduction of oceanic lithosphere beneath a continent. Examples include the Andes
and the Cascades.
Convergent plate boundary A boundary in which two plates move together, resulting
in oceanic lithosphere being thrust beneath an overriding plate, eventually to be
reabsorbed into the mantle. It can also involve the collision of two continental plates to
create a mountain system.
Core Located beneath the mantle, it is Earth’s innermost layer. The core is divided into
an outer core and an inner core.
Crater The depression at the summit of a volcano, or that which is produced by a
meteorite impact.
Craton That part of the continental crust that has attained stability; that is, it has not
been affected by significant tectonic activity during the Phanerozoic eon. It consists of
the shield and stable platform.
Creep The slow downhill movement of soil and regolith.
Cross-bedding Structure in which relatively thin layers are inclined at an angle to the
main bedding. Formed by currents of wind or water.
Cross-cutting A principle of relative dating. A rock or fault is younger than any rock
(or fault) through which it cuts.
Crust The very thin, outermost layer of Earth.
D
Dark silicate Silicate minerals containing ions of iron and/or magnesium in their
structure. They are dark in color and have a higher specific gravity than
nonferromagnesian silicates.
Debris flow A relatively rapid type of mass wasting that involves a flow of soil and
regolith containing a large amount of water; also called mudflows.
Deep-ocean basin The portion of seafloor that lies between the continental margin and
the oceanic ridge system. This region comprises almost 30 percent of Earth’s surface.
Deflation The lifting and removal of loose material by wind.
Deformation General term for the processes of folding, faulting, shearing,
compression, or extension of rocks as the result of various natural forces.
Density The weight per unit volume of a particular material.
Desert One of the two types of dry climate; the drier of the dry climates.
Dike A tabular-shaped intrusive igneous feature that cuts through the surrounding rock.
Disconformity A type of unconformity in which the beds above and below are parallel.
Discordant A term used to describe plutons that cut across existing rock structures,
such as bedding planes.
Distributary A section of a stream that leaves the main flow.
Divergent plate boundary A boundary in which two plates move apart, resulting in
upwelling of material from the mantle to create new seafloor.
Dry climate A climate in which the yearly precipitation is less than the potential loss of
water by evaporation.
E
Earthquake The vibration of Earth produced by the rapid release of energy.
Elastic deformation Nonpermanent deformation in which rock returns to its original
shape when the stress is released.
Erosion The incorporation and transportation of material by a mobile agent, such as
water, wind, or ice.
Evaporite A sedimentary rock formed of material deposited from solution by
evaporation of water.
External process Process such as weathering, mass wasting, or erosion that is powered
by the Sun and transforms solid rock into sediment.

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