Erosion: Page 1 of 8 Erosion - Wikipedia, The Free Encyclopedia
Erosion: Page 1 of 8 Erosion - Wikipedia, The Free Encyclopedia
Erosion: Page 1 of 8 Erosion - Wikipedia, The Free Encyclopedia
Erosion
From Wikipedia, the free encyclopedia
A certain amount of erosion is natural and, in fact, healthy for the ecosystem. For
example, gravels continually move downstream in watercourses. Excessive erosion,
however, can cause problems, such as receiving water sedimentation, ecosystem
damage (including dead fish) and outright loss of soil.
Contents
? 1 Causes
? 2 Erosion processes
? 2.1 Gravity erosion
? 2.2 Water erosion
? 2.3 Shoreline erosion
? 2.4 Ice erosion
? 2.5 Wind erosion
? 3 Tectonic effects of erosion
? 4 Materials science
? 5 Figurative use
? 6 Origin of term
? 7 See also
? 8 References
? 9 Further reading
? 10 External links
Causes
What causes erosion to be severe in some areas and minor elsewhere is a
combination of many factors, including the amount and intensity of precipitation,
the texture of the soil, the gradient of the slope, ground cover (from vegetation,
rocks, etc.) and land use. The first factor, rain, is the agent for erosion, but the
degree of erosion is governed by other factors. That definition is in thye form
geolgy. The first three factors can remain fairly constant over time. In general,
given the same kind of vegetative cover, you expect areas with high-intensity
precipitation, sandy or silty soils and steep slopes to be the most erosive. Soils with
a greater proportion of clay that receive less intense precipitation and are on gentle
slopes tend to erode less. But here, the impact of atmospheric sodium on erodibility
of clay should be considered.
The factor that is most subject to change is the amount and type of ground cover.
When fires burn an area or when vegetation is removed as part of timber operations
or building a house or a road, the susceptibility of the soil to erosion is greatly
increased.
Roads are especially likely to cause increased rates of erosion because, in addition
to removing ground cover, they can significantly change drainage patterns. A road
that has a lot of rock and one that is "hydrologically invisible" (that gets the water
off the road as quickly as possible, mimicking natural drainage patterns) has the
best chance of not causing increased erosion.
One of the main causes of erosive soil loss in the year 2006 is the result of slash
and burn treatment of tropical forests. When the total ground surface is stripped of
vegetation and then seared of all living organisms, the upper soils are vulnerable to
both wind and water erosion. In a number of regions of the earth, entire sectors of a
country have been rendered unproductive. For example, on the Madagascar high
central plateau, comprising approximately ten percent of that country's land area,
virtually the entire landscape is sterile of vegetation, with gully erosive furrows
typically in excess of 50 meters deep and one kilometer wide. Shifting cultivation is
a farming system which sometimes incorporates the slash and burn method in some
regions of the world.
Erosion processes
Gravity erosion
Slumping happens on steep hillsides, occurring along distinct fracture zones, often
within materials like clay that, once released, may move quite rapidly downhill.
They will often show a spoon-shaped depression, within which the material has
begun to slide downhill. In some cases, the slump is caused by water beneath the
slope weakening it. In many cases it is simply the result of poor engineering along
highways where it is a regular occurrence.
Surface creep is the slow movement of soil and rock debris by gravity which is
usually not perceptible except through extended observation. However, the term
can also describe the rolling of dislodged soil particles 0.5 to 1.0 mm in diameter
by wind along the soil surface.
Water erosion
Valley or stream erosion occurs with continued water flow along a linear feature.
The erosion is both downward, deepening the valley, and headward, extending the
valley into the hillside. In the earliest stage of stream erosion, the erosive activity is
dominantly vertical, the valleys have a typical V cross-section and the stream
gradient is relatively steep. When some base level is reached the erosive activity
switches to lateral erosion which widens the valley floor and creates a narrow
floodplain. The stream gradient becomes nearly flat and lateral deposition of
sediments becomes important as the stream meanders across the valley floor. In all
stages of stream erosion by far the most erosion occurs during times of flood, when
more and faster-moving water is available to carry a larger sediment load. In such
processes, it is not the water alone that erodes, suspended abrasive particles,
pebbles and boulders can also act erosively, as they traverse a surface.
At extremely high flows, kolks, or vortices are formed by large volumes of rapidly
rushing water. Kolks cause extreme local erosion, plucking bedrock and creating
pothole-type geographical features. Examples can be seen in the flood regions
result from glacial Lake Missoula, which created the channeled scablands in the
Columbia Basin region of eastern Washington.[1]
Shoreline
erosion
Sediment is transported along the coast in the direction of the prevailing current
(longshore drift). When the upcurrent amount of sediment is less than the amount
being carried away, erosion occurs. When the upcurrent amount of sediment is
greater, sand or gravel banks will tend to form. These banks may slowly migrate
along the coast in the direction of the longshore drift, alternately protecting and
exposing parts of the coastline. Where there is a bend in the coastline, quite often a
build up of eroded material occurs forming a long narrow bank (a spit). Underwater
sandbanks offshore may also protect parts of a coastline from erosion. Over the
years, as the sandbanks gradually shift, the erosion may be redirected to attack
different parts of the shore.
Ice erosion
Ice erosion is caused by movement of ice, typically as glaciers. Glaciers can scrape
down a slope and break up rock and then transport it, leaving moraines, drumlins
and glacial erratics in their wake, typically at the terminus or during glacier retreat.
Ice wedging is the weathering process in which water trapped in tiny rock cracks
freezes and expands, breaking the rock. This can lead to gravity erosion on steep
slopes. The scree which forms at the bottom of a steep mountainside is mostly
formed from pieces of rock broken away by this means. It is a common engineering
problem, wherever rock cliffs are alongside roads, because morning thaws can drop
hazardous rock pieces onto the road. In some places cold enough, water seeps into
rocks during the daytime, then freezes at night. Ice expands, thus, creating a wedge
in the rock. Over time, the repetition in the forming and melting of the ice causes
fissures, which eventually breaks the rock down.
Wind erosion
Wind erosion, also known as eolian erosion, is the movement of rock and sediment
by the wind. Windbreaks are often planted by farmers to reduce wind erosion. This
includes the planting of trees, shrubs, or other vegetation, usually perpendicular or
nearly so to the principal wind direction. The wind causes dust particles to be lifted
and therefore moved to another region. Wind erosion generally occurs in areas with
little or no vegetation, often in areas where there is insufficient rainfall to support
vegetation. An example is the formation of sand dunes, on a beach or in a desert.
Materials science
In materials science, erosion is the recession of surfaces by repeated localized
mechanical trauma as, for example, by suspended abrasive particles within a
moving fluid. Erosion can also occur from non-abrasive fluid mixtures. Cavitation
is one example.
In hard particle erosion, the hardness of the impacted material is a large factor in
the mechanics of the erosion. A soft material will typically erode fastest from
glancing impacts. Harder material will typically erode fastest from perpendicular
impacts. Hardness is a correlative factor for erosion resistance, but a higher
hardness does not guarantee better resistance. Factors that effect the erosion rate
also include impacting particle speed, size, density, hardness, and rotation.
Coatings can be applied to retard erosion, but normally can only slow the removal
Figurative use
The concept of erosion is commonly employed by analogy to various forms of
perceived or real homogenization (i.e. erosion of boundaries), "leveling out",
collusion or even the decline of anything from morals to indigenous cultures. It is a
common trope of the English language to describe as erosion the gradual, organic
mutation of something thought of as distinct, more complex, harder to pronounce or
more refined into something indistinct, less complex, easier to pronounce or
(disparagingly) less refined.
Origin of term
The first known occurrence of the term "erosion" was in the 1541 translation by
Robert Copland of Guy de Chauliac's medical text The Questyonary of Cyrurygens.
Copland used erosion to describe how ulcers developed in the mouth. By 1774
'erosion' was used outside medical subjects. Oliver Goldsmith employed the term in
the more contemporary geological context, in his book Natural History, with the
quote
See also
? Badland
? Bioerosion
? Biorhexistasy
? Groundwater sapping
? Erosion control
? Erosion prediction
? Riparian strips
? Surface runoff
? Weathering
References
1. ^ Alt, David. Glacial Lake Missoula & its Humongous Floods. Mountain Press
Publishing Company. ISBN 0-87842-415-6.
Further reading
External links
? Coastal Erosion Information from the Coastal Ocean Institute, Woods Hole
Oceanographic Institution
? International Erosion Control Association