Glossary - Fundamentals of the Physical Environment - page 880

Constructive margin The boundary between two diverging crustal plates where new
oceanic crust is formed.
Contact metamorphism Thermal metamorphism , involving chemical alteration or
recrystallization of rock in direct or close contact with a magma .
Continental drift The relative movement of continents over Earth's surface summarized
by Alfred Wegener in 1912 and now known to be part of the wider processes of plate
tectonics and sea-floor spreading.
Continental plate A tectonic plate dominated by light, granitic rocks and forming the
crustal basement of a continental land surface.
Continental rise The lowermost section of a submerged continental margin, which rises
gently from an abyssal plain before steepening into the continental slope .
Continental shelf The area of continental crust which lies below sea level and extends
beyond the coast as a shallow, gently sloping plain as far as the continental shelf
break ; with an average width of 70 km, it is more extensive on passive than on
convergent plate margins.
Continental slope The submerged continental margin seaward of the continental shelf
break which steepens and extends down to the continental rise .
Continuum A range of properties in which change occurs continuously and more or less
smoothly, rather than in an abrupt, stepwise manner or discontinuum.
Convection The process of heat transfer in a fluid, involving the movement of substantial
volumes of the fluid concerned. Convection is very important in the atmosphere and,
to a lesser extent, in the oceans and mantle .
Cordillera Mountain chains or ranges, usually long (10 3 km) but narrow (10 2 km) in
extent; subduction orogens typically form cordilleran mountain systems.
Core Earth's innermost, high-temperature and dense nickel-iron sphere.
Core - stone The residual, relatively unweathered core of a larger joint-bound block
whose outer parts are severely weathered or disintegrated.
Co - tidal line A line linking points on a map at which high tide occurs simultaneously,
usually measured in hours before or after the high tide at a suitable reference point.
Cover sand An extensive sand sheet, generally thin and lacking bedforms, covering a
land surface adjacent to a current or former ice sheet from whose fine-grained debris it
was deflated.
Craton An area of continental crust, generally stable throughout the Phanerozoic,
comprising a crystalline core or shield and marginal platform of metamorphic and
sedimentary rocks.
Creep Slow and continuous non-recoverable plastic deformation of rock mass, soil or ice
under gravitational stress accomplished by intergranular motion.
Crevasse A brittle fracture caused by extending flow in a moving glacier; also used to
define a channel breaching a river bank or levée .
Crevasse splay A fan of coarse alluvium spread over the flood plain from a channel
crevasse .
Crust Earth's outermost solid sphere, representing the upper part of the lithosphere and
differentiated into lighter, thicker continental crust and denser, thinner oceanic crust.
Crustal extension Crustal stretching and consequential thinning, achieved by faulting
and rifting, in response to a number of tectonic and geomorphic processes; it is
associated particularly with divergent plate boundaries.