This preview shows page 1. Sign up to view the full content.
Unformatted text preview: outhern Oscillation (ENSO) refers to the global coupling, or teleconnection, of
oceanic-atmospheric phenomena with weather in other areas. Specifically, the term is applied
to a warming trend during a small number of years of sea-surface water of the tropical eastern
Pacific Ocean, causing atmospheric-pressure differences in the southern hemisphere and
elsewhere (Southern Oscillation, SO) and short-term alteration of precipitation patterns; in arid
and semiarid areas of southwestern North America, for example, winter rainfall during El Niňo
years is typically greater than normal, as are streamflow and sediment movement.
Eluviation is the hydrologic process by which water percolates downward and out of a soil
zone, moving dissolved solids, colloids, and organic material from the surface through the A
horizon into the B horizon; precipitation of dissolved solids, especially as carbonate minerals, in
the B horizon may be an important process of calcrete formation.
Entrainment is the process by flowing water or air, or by the mixing of water or air between
opposing currents, of mobilizing sediment by picking up particles and transporting them in
suspension, as suspended load, and along the channel or other surface of transfer, as bed (or
traction) load; rates of hydrologic entrainment depend on stream power (the product of
discharge and water-surface slope) and the sizes of the sediment particles.
Eolian (or aeolian, from Aeolus, the Roman god of the winds) pertains to entrainment
processes of erosion and sediment transport, deposition, and translocation (mainly sorting) by
wind; eolian features include wind-blown sand forming dune fields, atmospherically deposited
silt and fine sand (loess) and volcanic ash (tuff), and erosional landforms such as yardangs.
Eolian dune, including eolian dune field, is an accumulation, or concentration, by depositional
processes of wind as a low, small-scale mound, ridge, or, more commonly, a complex (field, or
zone) of mounds and ridges, of loose, well sorted granular material (generally sand) that, if
active, may be bare or, if inactive, partially to fully vegetated; eolian dunes are subject to
translocation, without a basic loss of scale or structure, by the action of wind.
Ephemeral gully is a gully, typically in an agricultural field, that develops due to water erosion
during a growing season but which is subject to removal by any primary tillage operation.
Ephemeral stream describes streamflow within a normally dry channel; the streamflow occurs
inconsistently or infrequently and, except during periods when the ephemeral streamflows
occur, the channel bed is directly underlain by unsaturated alluvium. 19 Ephemeral-stream channel is a channel in which streamflow occurs inconsistently or
infrequently and, except during periods of streamflow, is directly underlain by unsaturated
alluvium or rock; ephemeral-stream channels are most common in arid and semiarid regions
and typically have a rectangular to steeply sided trapezoidal cross section, banks a meter or
more in height formed of fine-grained, poorly consolidated over-bank sediment, and a nearly
flat, sandy bed. Synonyms are dry wash, arroyo (northern Mexico and southwestern United
States), and wadi (southwestern Asia, Arabian Peninsula, and northern Africa)
Equifinality, when used in a geomorphic context, is a term to recognize that some landforms,
such as braided stream channels, are the end, or final, results of a wide range of possible
process sets yielding the observed landform; the concept of geomorphic equifinality is roughly
analogous to the biological concept of convergent evolution, which is an acknowledgement that
initially dissimilar species, if subjected to similar environmental conditions over long time
periods, may develop closely similar physical and behavioral characteristics. As applied to
watersheds, a range of different disturbances, both intrinsic and extrinsic, may ultimately yield
similar down-basin landforms; a braided stream channel is one of many examples.
Equilibrium, as a means of characterizing a geomorphic feature (such as a specified hillslope or
stream-channel reach), refers to the balance between inputs and outputs, mostly water,
dissolved solids, and sediment (including specific particle sizes), that must be attained to
achieve stability. Because fluxes of matter and energy are never constant in natural landscapes,
the term equilibrium, when applied to geomorphic systems, is generally modified by “dynamic”
or “quasi”, implying that the feature or process is time-integrated and adjusted to the range of
inflows and outflows typical of the system. The term is often used synonymously with
Erodibility is an expression of the susceptibility of a surface to the erosion process; thus, it is
the ease by which sediment, rock, or especially soil is detached and entrained, generally by
rainsplash, surface flow, or wind. Erodibility, in quantitative terms, is the loss in mass per unit
area of a sediment, rock, or soil surface that results from application of a known external
energy or she...
View Full Document
- Fall '13
- The Adventures of Tom Sawyer