Geoscience Reference
In-Depth Information
Cold-air drainage
The gravity flow of cold air by virtue
of its greater density.
Cold glacier
A glacier whose mass is of predominantly
cold, polythermal ice with thin surface and basal layers
periodically at
pressure-melting point
; typical of the greater
part of large ice sheets.
Cold seawater weathering
The chemical alteration of
rock at the sea bed by cold water, as distinct from
hydrothermal circulation, primarily by hydration,
although some oxidation may also occur.
Cold stage
A period of Earth history in which global
climates are significantly colder than at present: snow, ice
and
permafrost
cover large portions of continental land
surfaces and polar oceans, with prevailing
cryospheric
and
icehouse
conditions. Up to twenty cold stages have
dominated the Quaternary period and the term is more
appropriate than 'glacial period' or 'Ice Age' - glaciers were
absent from many areas for much of the time.
Colluvium
Granular debris accumulating towards the
base of slopes as a result of mass wasting of bedrock and
older slope deposits.
Columnar
A type of soil structure consisting of vertical
units with rounded tops; usually in the subsoil of alkaline
clays.
Competition
Between organisms with similar growth
requirements, and which compete for them.
Components
The pathways by which energy and matter
flow between elements of the system.
Compound translation failure
A slope failure event
involving two or more processes, such as rotation and
sliding, or sliding and flow, as material properties and
forces change after initial motion.
Compressive flow
A deceleration in glacier flow which
creates compressive stress, longitudinal crevasses and
thickening.
Compressive strength
The maximum compression an
Earth material may resist before failure occurs.
Compressive stress
The normal (right-angle) stress
which acts vertically or laterally on a unit of Earth material
which may lead to compression or crushing.
Conceptual model
A general model based on conceptual
and qualitative ideas of relationships.
Conduction
The process of heat transfer through matter
without movement of the matter itself. It is the process
whereby heat travels through solids.
Cone sheet
A
dyke
intruded upwards and radially
outwards from a
magma
reservoir, giving it a cone shape.
Conformable sequence
An unbroken rock-forming
sequence in which each successive layer forms undisturbed
contact with its predecessor, with little or no time
separation.
Connectance
The number of functioning ecological
links which connect the members of a defined com-
munity.
Constructive margin
The boundary between two div-
erging 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.