Geoscience Reference
In-Depth Information
Endogenetic
Energy supplied by Earth. It is mainly
derived from the hot interior of Earth.
Energy pyramids
Eutrophication
The process of making an environ-
ment (e.g. water or soil) well supplied with nutrients
('eutrophic') and therefore highly productive biologically.
Evaporation pan
An open water tank used to measure
evaporation; sizes vary between different countries.
Evaporite
A mineral or sedimentary rock precipitated
from a saline solution as a result of evaporation.
Evolution
Genetically controlled changes in physiology,
anatomy and behaviour that occur in a population over
time.
Evorsion
The corrosion of stream channel
potholes
by
pebbles swirled around by vortices and eddies.
Exchangeable cations
Cations which are held on
exchange sites on soil colloids and which are able to
exchange with cations in the soil solution.
Exchangeable sodium percentage (ESP)
The percentage
of the
cation exchange capacity
occupied by exchangeable
sodium ions; used as an index of soil alkalinity.
Exfoliation
Mechanical or physical weathering which
proceeds by the disintegration and removal of successive
layers of rock mass.
Exogenetic
Energy derived from outside Earth. The vast
majority of such energy is from the sun.
Explosive
Extrusive igneous activity characterized by
violent eruptions of
felsic
material through volcanic vents.
Extending flow
A zone of accelerated flow within a
glacier which creates tensile stress, lateral crevassing and
thinning.
Extrusive
A description of molten igneous material
which erupts at Earth's surface before cooling.
Facilitation model
A model of plant
succession
in which
a habitat is modified by a species in such a manner as to
favour its replacement by other species.
Factor of safety (F
s
)
A measure of the balance between
shear stress and shear strength in a slope; a state of
limiting
equilibrium
exists when shearing forces equal resisting
forces in a slope and
F
s
= 1.
Facultative relationships
The pyramidal structure of
all
ecosystems
when measured by the flow of energy.
Entisol
A soil order in the USDA classification
characterized by shallow soils lacking distinct horizons.
Epeirogenesis
The elevation or depression of large areas
of crust without major deformation, in contrast to
orogenesis
, resulting from either thermal or mechanical
processes.
Ephemeral stream flow
Intermittent stream flow
through all or part of a channel generated only by
precipitation events and common in arid and semi-arid
zones.
Epicontinental sea
A partially enclosed marine basin on
continental crust linked to an adjacent ocean (cf.
marginal
sea
).
Epsilon diversity
Species diversity in a broad region
(1-100 million ha) with varied landscapes.
Equatorial counter-current
An eastward, equatorial
gravity flow driven by the slight westerly rise in the
ocean surface stacked up by more pronounced westerly
currents.
Equilibrium
The state of a system which over time tends
to maintain its general structure and character in
sympathy with the processes acting upon it.
Equilibrium line altitude (ELA)
The altitude which marks
the surface boundary between the upper accumulation
and lower ablation zones of a glacier; it may be taken as
the position at the end of an ablation (summer) season
or the average position over several years.
Equitability
A measure of ecological diversity based on
information theory.
Erg
A sand desert or large sand sea.
Erodibility
The susceptibility of
Earth materials to
erosion.
Erosion
Any dynamic process which causes the removal
of Earth materials, distinguished here from
weathering
,
denudation
and
mass wasting
.
Erosivity
The erosive power of a stream or other agent.
Erratic
A rock fragment transported away from its
source and recognizable as such after it has left the outcrop
of its parent lithology.
Esker
The alluvial bed of an en- or subglacial stream
which may survive as a long, sinuous partially collapsed
debris ridge.
Etch front
The boundary separating weathered from
unweathered rock, at the landscape rather than individual
rock scale.
Eustatic
Relating to global sea-level oscillation caused by
absolute changes in sea-water volume.
Relationships which exist
under various conditions.
Fall velocity
The specific velocity below which a moving
fluid is unable to sustain a given particle size in
suspension; or the rate at which suspended particles settle
through a fluid.
Fall wind
Any wind characterized by its descent of
leeward mountain slopes, irrespective of its thermal
character and origins.
Falling limb
The expression on a
hydrograph
of the
subsiding
quickflow
component of stream discharge.
Fatigue
The progressive weakening of a material
through cyclic application and removal of sub-critical
stress which leads to its eventual failure.
