Geoscience Reference
In-Depth Information
underwater and ice-marginal sediment-landform
associations.
Glaciomarine sediment
Rock debris released into the sea
from
tidewater glaciers
,floating
ice shelves
and
icebergs
.
Glaciotectonic
Said of the deformation of ice, bedrock
and sediment by glacier ice flow and consequent fold,
thrust and shear structures.
Gleying
Soil processes characteristic of wet or water-
logged soils; usually denoted by bluish-grey colours
and reddish mottles, produced by a complex series of
oxidation and reduction reactions.
Global hydrological cycle
The global stores and transfers
of water in its liquid, solid and gas phases.
Global Ocean Conveyor
A slow, three-dimensional
ocean current system transferring warmer surface and
intermediate water polewards, with a return equator-
ward flow of deep, cold water (see also
thermohaline
circulation
).
Gouge
Fundamental niche
The maximum area, in terms of
space, time and function, which a species would be capable
of occupying in the absence of competition from other
species.
Gabbro
A basic,
coarse-grained igneous rock;
the
intrusive near equivalent of
basalt
.
Gamma diversity
The total biodiversity of a defined
geographical region.
Geochemical cycle
The movement of rock minerals
which accompanies the
rock cycle
, characterized by
aggregation, disaggregation,
fractionation
, refinement,
changes of state and the formation of new species as rock
mass itself is cycled.
Geoecology
An integrated discipline which studies
interactions between geological, geomorphic, ecological
and meteorological components of the landscape.
Geological process
A process usually involving or
associated with Earth's near surface or interior rocks, and
distinct from - or combined with -
geomorphological
process
.
Geomorphic
Soft, fine-grained debris lining a fault or mineral
vein.
Graben
A down-faulted rock mass flanked by parallel
faults and often forming a structural valley.
Grade
A property of soil structure which describes the
strength or stability of soil aggregate development.
Gradients
Pertaining to Earth's surface landforms and
their study.
Geomorphological process
A process involved in the
formation and alteration of the landforms at Earth's land
surface.
Genetic drift
Changes in the genetic composition of a
population as new genes are formed by mutation and
others lost by random processes.
Geophytes
A class of plants which reproduce from
bulbs, corms, rhizomes or tubers.
Geothermal heat flow
The heat loss from Earth's interior
to space, measured at an average Earth surface flux of 82
mW m
-2
but locally varying according to the proximity
of hot spots, volcanoes, etc.
Gibber
A desert rock surface covered with
lag gravels
.
Gilbert-type delta
A 'classic' fan delta with successive
overlapping topset, foreset and bottomset beds on the
prograding
surface, advancing front and distal slope
respectively.
Glacier
A large accumulation of terrestrial ice and
superficial snow, metamorphosed from annual snowfall
and other precipitation and capable of deformation and
flow under its own mass.
Glacio-eustatic
The change in ocean water volume and
global sea level in response to the growth and decay of ice
sheets and glaciers, which has dominated Quaternary sea-
level change.
Glacio-isostatic rebound
The
isostatic
uplift of a land
surface formerly supporting an ice sheet, due to the
removal of the weight of ice and eroded rock.
Glaciomarine
Said of the interaction between
glacier
ice, floating shelf ice,
icebergs
and sea water, creating
Changes in environmental conditions along
a gradient.
Grain ballistics
Collisions between moving and
stationary particles in a fluid boundary layer in which
energy transferred to stationary particles moves them
horizontally or entrains them in the flow.
Granite
A coarse-grained
intrusive
igneous rock.
Gravitational energy
The potential energy acquired by
virtue of an object's distance, or further displacement
away, from Earth's centre; it plays an important role in
tectonic processes in the mantle and crust and in
geomorphic processes at the surface.
Gravitational water
The class of soil moisture which
drains from a saturated soil under the influence of gravity;
it is approximately equivalent to water held in pores larger
than 0.05 mm diameter.
Gravity
The force exerted on any body by Earth's mass
and axial rotation; it is an important endogenetic source
of energy for geological and geomorphic processes at or
near Earth's surface.
Greenhouse effect
The condition in which Earth's
average global temperatures are normally higher than
predicted by radiation laws by virtue of the presence of
substances in the lower atmosphere capable of absorbing
outgoing long-wave radiation.
Grey box
A partially understood system, in which
interest is centred on a restricted number of subsystems
and the remainder are ignored.
