Glossary - Fundamentals of the Physical Environment - page 729

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.
Crustal shortening Crustal compression and conse-
quential thickening, achieved by folding and thrusting,
and associated particularly with convergent plate
boundaries.
Crustal thickening An increase in crustal thickness
caused by intracontinental thrusting in an A-subduction
zone, where the buoyancy of light continental crust
precludes B-subduction and resorption ; isostatic balance is
maintained by the displacement of denser crust below the
thickened pile.
Crusting The reduction of soil infiltration capacity by
surface compaction during heavy rainfall, the dispersal of
fine grains into pores and subsequent drying.
Crustose lichens Lichens with flat, crust-like growth
form; lichens are symbiotic associations between a fungus
and an alga.
Cryofracture An alternative term for frost shattering .
Cryonival Said of processes related to the combination
or close proximity of snow and ice, such as frost
weathering at the margins of a snow patch and driven by
its diurnal thaw-freeze.
Cryopedology Soil-forming processes occurring in low-
temperature conditions,

Cut and fill The erosion and subsequent sedimentation
of new fluvial channels cut through existing fluvial
sediments, and the sedimentary structures so formed.
Cyclical climax theory The theory of climax vegetation
which emphasizes cyclical rather than unidirectional
change; mostly discussed in relation to tropical forests.
Darcy's law A definition of the relation between the
transmission of water through porous Earth material,
water viscosity and the height of the free water surface
above the point of measurement.
Debris cone A cone-shaped mass of rounded boulders
deposited where a mountain stream meets a flat valley
floor.
Debris flow A mass wasting process in which fluidized
colluvium or other loose, granular debris moves downhill
in a series of rapid turbulent pulses.
Decalcification The removal of carbonates (mostly
calcium carbonate) from a soil horizon.
Décollement A zone along which overlying rocks or
other Earth materials have become detached from and
have moved over underlying materials, normally as the
materials respond to shear stress.
Decomposers

Organisms that feed on dead or decaying

organic matter.
Deflation The removal by wind of fine granular

materials, especially sand, silt and snow.
Deflation hollow A surface depression in a material
which has undergone deflation or been abraded by wind-
blown sand.
Deformation The alteration of Earth material from an
initial shape and internal structure, involving compres-
sion, extension, folding , faulting , shear, etc.
Delayed flow An estimated component of stream flow
which is delayed in reaching the channel after a
precipitation event but does not form part of the baseflow .
Delta diversity Change in species diversity across varied
regions along a major gradient, e.g. of climate or relief.
Denitrification Bacterial processes occurring in soils, in
the absence of free oxygen, to break down nitrates and
nitrites with the evolution of free nitrogen.
Denudation The combined processes of weathering ,
mass wasting and erosion which cause the disaggregation
of rock mass and its removal to lower-lying ground;
denudation may proceed far enough to cause the virtual
destruction and levelling of continental crust down to sea
level .
Denudation chronology A scheme of land surface
development which saw many variations developed over
almost a century up to the 1960s, based on belief in a
denudation cycle ;modern plate tectonics provides more
realistic mechanisms but more complex geomorpho-
logical histories.

usually in the presence of

permafrost .
Cryophyte A cold-tolerant plant of the arctic-alpine
community with life forms and cycles adapted to
persistent snow and ground ice.
Cryosphere The portion of Earth's hydrosphere where
water is perennially frozen as snow, glacier or ground ice .
Cryoturbation Sum of all processes of frost heave, stone
reorientation and 'overturning' that occur within the soils
and superficial deposits in periglacial regions.