Environmental Engineering Reference
In-Depth Information
Elastic
A material condition in which strain (deformation, or change of shape) is wholly
and immediately recoverable upon the removal of stress.
Elastic strain release
The restoration of the original shape of a material which has
experienced elastic deformation, when the stress which caused it is released; thus rock
which deformed elastically when compressed will expand on 'pressure release' and
may fracture if the recovery is imperfect.
Electrical conductivity
(
EC
) The ability of a soil to conduct an electric current; used as
an index of soil salinity.
Eluviation
The removal of suspended solids or mineral colloids from a higher to a lower
soil horizon by water percolation.
Emerson model
A model of soil aggregate formation involving clay domains, organic
linkages and quartz particles.
Endogenetic
Energy supplied by Earth. It is mainly derived from the hot interior of
Earth.
Energy pyramids
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
).
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.