Difference between revisions of "Erosion" - New World Encyclopedia

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[[Image:Erosion.jpg|thumb|225px|Severe soil erosion in a wheat field near Washington State University, USA.]]
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[[Image:Erosion.jpg|thumb|300px|Severe soil erosion in a wheat field near Washington State University, U.S.A.]]
  
'''Erosion''' is the displacement of  solids ([[soil]], [[mud]], [[Rock (geology)|rock]] and other particles) by the agents of wind, water, or ice, by downward or down-slope movement in response to [[gravity]], or by living organisms (in the case of [[bioerosion]]). Erosion is distinguished from [[weathering]], or the decomposition of rock and particles through processes in which no movement is involved, although the two processes may be concurrent.
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In [[geology]] and [[environmental science]], '''erosion''' is the displacement of  solids ([[soil]], [[mud]], [[Rock (geology)|rock]] and other particles) by the agents of wind, water, ice, or living organisms, or by down-slope movement in response to [[gravity]]. Erosion needs to be distinguished from [[weathering]], although the two processes may be concurrent. Weathering refers to the decomposition of rock and minerals through processes involving no movement, that is, no physical removal of material.
  
Erosion is an intrinsic natural process but in many places it is increased by human [[land use]]. Poor land use practices include [[deforestation]], [[overgrazing]]*, unmanaged construction activity and road or trail building. However, improved land use practices can limit erosion, using techniques like [[Terrace (agriculture)|terrace]]*-building, or the leveling of the land interrupting steep slopes <"Terrace." The Free Dicitionary by Farlex. http://www.thefreedictionary.com/terrace>,  and tree planting.
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Erosion is a natural process, moving material and nutrients from one place to another and converting rock into soil. Thus a certain degree of erosion is healthy for the [[ecosystem]]. Excessive erosion, however, can damage the ecosystem, such as by increased water [[sediment]]ation or the outright loss of soil.
 
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A certain amount of erosion is natural and, in fact, healthy for the [[ecosystem]]. For example, [[gravel]]s continually move downstream along watercourses. Excessive erosion, however, can cause problems, such as increasing water [[sediment]]ation, ecosystem damage and the outright loss of soil.
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In many places, erosion is heightened by human [[land use]]. Poor land-use practices include [[deforestation]], [[overgrazing]], unmanaged construction activity, and road or trail building. On the other hand, improved land-use practices can limit erosion, by techniques such as tree planting and [[Terrace (agriculture)|terrace]]-building, or leveling of the land interrupting steep slopes.<ref>[http://www.thefreedictionary.com/terrace "Terrace"] The Free Dictionary by Farlex.</ref>
  
 
==Causes==
 
==Causes==
  
What causes erosion to be more severe in some areas and less in others is a combination of many factors, including the amount and intensity of [[rainfall|precipitation]], the [[Soil texture|texture]] of the soil, the gradient of the slope, ground cover (from [[vegetation]], rocks, etc.) and land use. Though rain is the first and major agent of erosion, the degree of erosion is governed by the other factors listed.
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Erosion is governed by a combination of factors, including the amount and intensity of [[precipitation]] (particularly [[rain]]), [[soil texture]], gradient of the slope, ground cover (from [[vegetation]], rocks, and so forth), and land use. Of these, the main agent of erosion is rainfall.
  
The first three factors mentioned above can remain fairly constant over time. In general, given the same kind of vegetative cover, you expect areas with high-intensity precipitation, [[sand]]y or [[silt]]y soils, and steep slopes to be the most erosive. Soils with a greater proportion of [[clay]] that receive less intense precipitation and are situated along lower slope gradients tend to erode less.
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In general, if one compares areas with the same degree of vegetative cover, erosion tends to be higher in areas with high-intensity precipitation, [[sand]]y or [[silt]]y soils, and steep slopes. On the other hand, there is less erosion of soils with a higher content of [[clay]], situated along lower slope gradients, and receiving less intense precipitation.
  
Among the factors listed above, the one most subject to change over time is the amount and type of ground cover. When fires burn an area or when vegetation is removed as part of the process of timber operations or building a house or a road, a soil's susceptibility to erosion is greatly increased. The construction of roads are likely to cause increased rates of erosion because, in addition to removing vegetative ground cover, they can significantly alter drainage patterns. However, 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.  
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Among the factors listed above, the one most likely to change over time is the amount and type of ground cover. When fires burn an area, or when vegetation is removed during timber operations or house or road construction, a soil's susceptibility to erosion is greatly increased. Road construction can increase the rate of erosion because, in addition to removing vegetative ground cover, it can significantly alter drainage patterns. However, erosion is minimized if the road has a lot of rock and is "hydrologically invisible," that is, the water flows off the road as quickly as possible, mimicking natural drainage patterns.  
  
[[Image:Bank erosion 5790.JPG|thumb|200 px|right|Bank erosion started by four-wheeler, all-terrain vehicles in Yauhanna, South Carolina.]]
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[[Image:Bank erosion 5790.JPG|thumb|200 px|left|Bank erosion started by four-wheeler, all-terrain vehicles in Yauhanna, South Carolina.]]
  
Changes in the kind of vegetation in an area can also effect erosion rates. Different kinds of vegetation effect the infiltration rates of rain into the soil. Forested areas are able to take up water at higher rates, so precipitation there results in less surface runoff, and subsequently, less erosion of surface materials. In these areas, much of the water goes into subsurface flows, which are generally less erosive. Leaf litter and low shrubs also contribute to the high infiltration rates of forested systems, and removing them can lead to an increase in erosion rates. Leaf litter also shelters the soil from the impact of falling raindrops, which is a significant agent of erosion. Vegetation can also change the speed of surface runoff flows, so the presence of grasses and shrubs play an important role in this respect as well.
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Changes in the type of vegetation in an area can also affect erosion rates. Different kinds of vegetation have an effect on the rates of infiltration of rain into the soil. Forested areas can take up water at higher rates, so precipitation there results in less surface runoff, and subsequently, less erosion of surface materials. In these areas, much of the water goes into subsurface flows, which are generally less erosive. Leaf litter and low shrubs also contribute to the high infiltration rates of forested systems, and removing them can lead to an increase in erosion rates. Leaf litter also shelters the soil from the impact of falling raindrops, which is a significant agent of erosion. Vegetation can also change the speed of surface runoff flows, so the presence of grasses and shrubs plays an important role in this respect as well.
  
Many human activities, like [[logging]] and heavy [[grazing]] by livestock can reduce vegetation from an area, making the soil more susceptible to 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]] [[forest]]s. 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 scattered along the landscape (typically larger than 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.
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Many human activities, such as [[logging]] and heavy [[grazing]] by livestock, can reduce an area's vegetation, making the soil more susceptible to increased erosion. One of the main causes of erosive soil loss in the year 2006 was the result of "[[slash-and-burn]]" treatment of [[tropical]] [[forest]]s. When the total ground surface is stripped of vegetation and seared of all living organisms, the upper soils are vulnerable to erosion by both wind and water. In a number of regions of the world, entire sectors of a country have been rendered unproductive. For example, on the [[Madagascar]] high central [[plateau]], constituting approximately 10 percent of that country's land area, virtually the entire landscape is sterile of [[vegetation]], with gully erosive furrows scattered along the landscape&mdash;typically more than 50 meters deep and one kilometer wide. [[Shifting cultivation]] is a farming system that sometimes incorporates the slash-and-burn method in some regions of the world.
  
When land is overused by animal activities (including humans), there can be mechanical erosion as well as removal of vegetation, leading to erosion. In the case of the animal kingdom, this effect materializes primarily with very large animal [[herd]] stampedes, such as the [[Blue Wildebeest]] on the [[Serengeti]] plain. Even in this case there are broader material benefits to the ecosystem, such as continuing the survival of grasslands, that are indigenous to this region. This effect may be viewed as anomalous or a problem only when there is a significant imbalance or [[overpopulation]] of one species.
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When land is overused by human and animal activities, there can be mechanical erosion as well as removal of vegetation, leading to erosion. In the case of animals, one sees this effect primarily with large [[herd]] stampedes, such as the [[Blue Wildebeest]] on the [[Serengeti]] plain. Even in this case, there are broader material benefits to the ecosystem, such as continuing the survival of grasslands indigenous to that region. This effect may be viewed as a problem only when there is a significant imbalance or [[overpopulation]] of one species.
  
In the case of human use, the effects are also generally linked to [[overpopulation]]. For example, when large numbers of hikers use trails or extensive off roading by vehicles occurs, erosive effects often follow, arising from vegetation removal and furrowing of foot traffic and off road vehicle tires. These effects can also accumulate from a variety of outdoor human activities, again arising from too many people using a finite land resource.  
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In the case of human use, the effects are also generally linked to [[overpopulation]]. For example, when large numbers of hikers use the same trails, or when there is extensive off-roading by vehicles, erosive effects often follow, arising from vegetation removal and furrowing of the soil. These effects can also accumulate from a variety of outdoor human activities, again arising from too many people using a finite land resource.  
  
One of the most serious and long-running water erosion problems worldwide is in [[China]], on the middle reaches of the [[Yellow River]] and the upper reaches of the [[Yangtze River]]. From the [[Yellow River]], over [[1 E12 kg|1.6 billion tons]] of sediment flow into the ocean each year. The [[sediment]] originates primarily from water erosion in the [[Loess Plateau]] region of northwest China.
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One of the most serious and long-running water erosion problems worldwide is in [[China]], around the middle reaches of the [[Yellow River]] and the upper reaches of the [[Yangtze River]]. From the Yellow River, over [[1 E12 kg|1.6 billion tons]] of sediment flow into the ocean each year. The [[sediment]] originates primarily from water erosion in the [[Loess Plateau]] region of northwest China.
  
 
== Erosion processes ==
 
== Erosion processes ==
[[image:Erosion2.jpg|thumb|left|A heavily eroded roadside near Ciudad Colon, Costa Rica.]]
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[[image:Erosion2.jpg|thumb|right|200px|A heavily eroded roadside near Ciudad Colon, Costa Rica.]]
  
 
===Gravity erosion===
 
===Gravity erosion===
  
''[[Mass wasting]]'' is the down-slope movement of rock and sediments, mainly due to the force of [[gravity]]. Mass wasting is an important part of the erosional process, as it moves material from higher elevations to lower elevations where transporting agents like streams and [[glacier]]s can then pick up the material and move it to even lower elevations. Mass-wasting processes are occurring continuously on all slopes. Some mass-wasting processes act very slowly, while others occur very suddenly, often with disastrous results. Any perceptible down-slope movement of rock or sediment is often referred to in general terms as a [[landslide]]. However, landslides can be classified in a much more detailed way that reflects the mechanisms responsible for the movement and the velocity at which the movement occurs. One of the visible topographical manifestations of a very slow type of a landslide is a [[scree]] slope.
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"[[Mass wasting]]" is the down-slope movement of rock and sediments, caused mainly by the force of [[gravity]]. Mass wasting is an important part of the erosion process, as it moves material from higher elevations to lower elevations, where transporting agents like streams and [[glacier]]s can pick up the material and move it further down. Mass-wasting processes occur continuously on all slopes. Some of these processes take place very slowly; others occur very suddenly, often with disastrous results.
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Any perceptible down-slope movement of rock or sediment is often referred to in general terms as a "[[landslide]]." There are, however, more detailed ways of classifying landslides, reflecting the mechanisms responsible for the movement and the velocity at which the movement occurs. One visible topographical manifestation of a very slow type of landslide is a [[scree]] slope.
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"[[Slump]]ing" is a form of mass-wasting in which consolidated materials or rock layers move together a short distance down a slope. Slumping happens on steep hillsides, and often with materials like [[clay]] that, once released, may move rapidly downhill. The area left behind by the moving material often shows a spoon-shaped depression. In some cases, the slump is caused by water beneath the slope, weakening layers of rock above it. In many cases, it is simply the result of poor engineering along [[highway]]s, where it is a regular occurrence.<ref>Parts adapted from 'Slump' in Wikipedia.</ref>
  
''[[Slump]]ing'' is a form of mass-wasting in which consolidated materials or rock layers move together a short distance down a slope. Slumping happens on steep hillsides, and often with materials like [[clay]] that, once released, may move quite rapidly downhill. The area left behind by the moving material will often show a spoon-shaped depression. In some cases, the slump is caused by water beneath the slope, weakening layers of rock above it. In many cases it is simply the result of poor engineering along [[highway]]s, where it is a regular occurrence. <parts adapted from 'slump' in Wiki>
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"Surface creep" is the slow movement of soil and rock debris by gravity. It is usually not perceptible, except through extended observation. This term, however, is also used to describe the rolling of dislodged soil particles (0.5 to 1.0 mm in diameter) by wind along the soil surface.
  
''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.
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[[Image:Tregastel_Brittany_France_Curious_Stone.jpg|thumb|left|A nearly perfect sphere of granite, in Trégastel, Brittany.]]
  
 
===Water erosion===
 
===Water erosion===
[[Image:Tregastel_Brittany_France_Curious_Stone.jpg|thumb|Nearly perfect sphere in [[granite]], [[Trégastel]], [[Brittany]].]]
 
  
Splash erosion is the detachment and airborne movement of small soil particles upon the impact of raindrops on falling on the soil. Sheet erosion is the result of heavy rain on bare soil, where water flows as a sheet down a gradient, carrying soil particles. In any area where precipitation rates exceed the absorbtion and infiltration rates into the soil, runoff occurs. Surface runoff turbulence can often cause more erosion than the initial raindrop impact '''[why?].''' [[Gully]] erosion results where water flows along a '''linear depression''', eroding a trench or gully.
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"Splash erosion" is the detachment and airborne movement of small soil particles, caused by the impact of raindrops falling on the soil. "Sheet erosion" is the result of heavy rain on bare soil, where water flows as a sheet down a gradient, carrying soil particles. In any area where precipitation rates exceed the absorption and infiltration rates into the soil, runoff occurs. Surface runoff turbulence can often cause more erosion than the initial raindrop impact. "[[Gully]] erosion" occurs in places where water flows along a linear depression, eroding a trench or gully (a furrow in the soil that is more than one meter deep).<ref>Anders Rapp, "Soil Erosion and Sedimentation in Tanzania and Lesotho." ''Ambio'' 4 (4): 154-163. Royal Swedish Academy of Sciences, 1975.</ref>
  
Valley or stream erosion occurs with continued water flow along a linear feature. The erosion is both [[downcutting|downward]], deepening the valley, and [[headward erosion|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 [[meander]]s across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood, when greater amounts and faster-moving water is available to carry a larger sediment load. In such processes, it is not only water that erodes, suspended abrasive particles, like [[pebbles]] and [[boulders]], can also act erosively as they traverse a surface.
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"Valley" or "stream erosion" takes place with continued water flow along a linear feature. The erosion is both [[downcutting|downward]], deepening the valley, and [[headward erosion|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-shaped 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 [[meander]]s (twists and turns) across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood, when greater amounts and faster-moving water is available to carry a larger sediment load. In such processes, erosion is caused not only by water but also by suspended abrasive particles, such as [[pebbles]] and [[boulders]], as they traverse the surface.
  
At extremely high flows, [[kolk]]s, or underwater [[vortex|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 having resulted from glacial activity [[Lake Missoula]], which created the [[channeled scablands]] in the [[Columbia Basin]] region of eastern [[Washington]].<ref> {{cite book''
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At extremely high rates of flow, [[kolk]]s (underwater [[vortex|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 that resulted from glacial activity at [[Glacial Lake Missoula]], which created the [[channeled scablands]] in the [[Columbia basin]] region of eastern [[Washington]] state.<ref>David Alt. ''Glacial Lake Missoula & its Humongous Floods.'' (Mountain Press Publishing Company, 2001. ISBN 0878424156).</ref> <ref>Lyn Topinka, ''[http://vulcan.wr.usgs.gov/Glossary/Glaciers/IceSheets/description_lake_missoula.html Topinka, Lyn, "Glacial Lake Missoula and the Missoula Floods"].'' USGS/Cascades Volcano Observatory, Vancouver, Washington, July 5, 2002. Accessed on November 28, 2006.</ref>
|first=David
 
|last=Alt
 
|id=ISBN 0-87842-415-6
 
|location=
 
|title=Glacial Lake Missoula & its Humongous Floods
 
|publisher=Mountain Press Publishing Company
 
}} </ref>
 
  
[[Image:Wavecut_platform_southerndown_pano.jpg|thumb|left|340px|[[Wave cut platform]] caused by erosion of cliffs by the sea, at [[Southerndown]] in South [[Wales]]]]
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===Shoreline erosion===
  
===Shoreline erosion===
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[[Image:Wavecut_platform_southerndown_pano.jpg|thumb|right|300px|Wave-cut platform caused by erosion of cliffs by the sea, at Southerndown in South Wales.]]
[[image:Coastal_Erosion.jpg|thumb|225px|Coastal erosion at [[Happisburgh]], [[Norfolk]], [[England]].]]
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[[image:Coastal_Erosion.jpg|thumb|225px|Coastal erosion at Happisburgh, Norfolk, England.]]
  
Shoreline erosion, on both exposed and sheltered coasts, primarily occurs through the action of currents and waves, but sea level (tidal) change can also play a role. '''Hydraulic action takes place''' when air in a ''joint'' is suddenly compressed by a wave closing the entrance of it. This then cracks it. Wave pounding is when the sheer energy of a wave hitting a cliff or rock breaks pieces off. Abrasion or Corrasion is caused by waves launching seaload at the cliff. It is the most effective and rapid form of shoreline erosion (not to be confused with Corrosion). Corrosion is the dissolving of rock by carbonic acid in sea water. Limestone cliffs are particularly vulnerable to this kind of erosion due to their porosity. Finally, Attrition is where particles/seaload carried by the waves are worn down as they hit each other and rock surfaces like cliffs. This then makes the material easier to wash away.
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Shoreline erosion, on both exposed and sheltered coasts, occurs primarily through the action of currents and waves, but sea level (tidal) changes can also play a role. When the sheer energy of a wave hitting a cliff or rock breaks pieces off, this is known as wave pounding. "Abrasion" or "corrasion" is caused by waves launching seaload at the cliff. It is the most effective and rapid form of shoreline erosion. (Corrasion should not to be confused with corrosion, or the dissolving of rock by carbonic acid in seawater. Limestone cliffs are particularly vulnerable to this type of erosion). Finally, "attrition" is where particles/seaload carried by the waves are worn down, as they strike one another and rock surfaces like cliffs, making the material easier to wash away.
  
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 impact different parts of the shore.
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Sediment is transported along the coast in the direction of the prevailing current (known as "longshore drift"). Erosion occurs when the uptake of new sediment by the upcurrent is less than the amount being carried away. 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 buildup of eroded material occurs, forming a long, narrow bank (or "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 impact different parts of the shore.
  
 
===Ice erosion===
 
===Ice erosion===
  
Ice erosion is caused by movement of ice, typically as glaciers. [[Glacier]]s can scrape down a slope and break up rock and then transport it, leaving [[moraine]]s, [[drumlin]]s and [[glacial erratic]]s in their wake, typically at the terminus or during [[Retreat of glaciers since 1850|glacier retreat]]. ''Ice wedging'' is the weathering process in which water trapped in tiny cracks of rock 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.
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Ice erosion is caused by the movement of ice, typically in the form of glaciers. As [[glacier]]s scrape down slopes, they break up rock and transport it, leaving [[moraine]]s (accumulation of rock debris), [[drumlin]]s (elongated hills or ridges), and [[glacial erratic]]s (pieces of glacial residue) in their wake, typically at the glacial terminus or during [[Retreat of glaciers since 1850|glacial retreat]].<ref>[http://education.yahoo.com/reference/dictionary/entry/drumlin "Drumlin"] ''The American Heritage Dictionary of the English Language,'' Fourth Ed. (Houghton Mifflin Company, 2000).Retrieved May 24, 2008. </ref> <ref>[http://education.yahoo.com/reference/dictionary/entry/moraine "Moraine"]. ''The American Heritage Dictionary of the English Language,'' Fourth Ed. (Houghton Mifflin Company, 2000). Retrieved May 24, 2008.</ref>
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"Ice wedging" is the weathering process in which water trapped in tiny cracks of rock freezes and expands, breaking the rock, allowing for gravity erosion on steep slopes. The [[scree]] that 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.
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In some places that are 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.
 
In some places that are 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===
  
'''Wind erosion''', also known as [[eolian processes|eolian]] erosion, is the movement of rock and sediment by the wind. The wind causes dust particles to be lifted up, where thay can be moved to other regions. 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. 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.  
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Wind erosion, also known as "[[eolian processes|eolian]] erosion," is the movement of rock and sediment by wind. The wind causes dust particles to be lifted up, where they can be moved to other regions. Wind erosion generally occurs in areas with little or no vegetation, often in places where there is insufficient rainfall to support vegetation. An example is the formation of sand [[dune]]s on a beach or in a desert. Farmers often plant ''windbreaks'' to reduce wind erosion. This includes the planting of trees, shrubs, or other vegetation, usually perpendicular (or nearly so) to the principal wind direction.
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=== Bioerosion ===
 
=== Bioerosion ===
  
'''Bioerosion''' describes the [[erosion]] of hard ocean [[substrate]]s by living organisms by a number of mechanisms. Bioerosion can be caused by [[mollusk]]s, [[Polychaete|polychaete worms]], [[sponge]]s, [[crustaceans]], [[Echinoderm|echinoid]]s, and [[fish]]. It can occur on [[coastline]]s, on coral [[reef]]s, and on [[ship]]s. Mechanisms of bioerosion include biotic [[boring]], [[drilling]], rasping, and scraping.
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Bioerosion involves the erosion of hard ocean [[substrate]]s by living organisms, utilizing a number of mechanisms. It can be caused by [[mollusk]]s, [[Polychaete|polychaete worms]], [[sponge]]s, [[crustaceans]], [[Echinoderm|echinoid]]s, and [[fish]]. It can occur on [[coastline]]s and coral [[reef]]s, and on the hulls of [[ship]]s. Mechanisms of bioerosion include biotic [[boring]], [[drilling]], rasping, and scraping.
  
Bioerosion of coral reefs generates the fine and white [[coral sand]] characteristic of tropical islands. The coral is converted to sand by internal bioeroders such as [[algae]], [[fungi]], [[bacteria]] (microborers) and [[sponge]]s ([[Clionidae]]), [[bivalve]]s ([[Lithophaga]]), [[sipunculan]]s ([[Aspidosiphon]]), polychaetes ([[Eunicidae]]), generating extremely fine sediment of 10 to 100 micrometres. External bioeroders include [[urchin]]s ([[Diadema, genus|Diadema]]) and [[chiton]]s ([[Acanthopleura]]). The combination of these internal and external bioeroders result in a great deal of erosion. [[Sea urchin]] erosion of calcium carbonate (CaCO3) has been reported in some reefs at annual rates exceeding 20 kg/m².  
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Bioerosion of coral reefs generates the fine and white [[coral sand]] characteristic of tropical islands. The coral is converted to sand by internal bioeroders such as [[algae]], [[fungi]], [[bacteria]], [[sponge]]s ([[Clionidae]]), [[bivalve]]s ([[Lithophaga]]), [[sipunculan]]s ([[Aspidosiphon]]), and polychaetes ([[Eunicidae]]), generating extremely fine sediment (10 to 100 micrometers in diameter). External bioeroders include [[urchin]]s ([[Diadema, genus|Diadema]]) and [[chiton]]s ([[Acanthopleura]]). The combination of these internal and external bioeroders results in a great deal of erosion. [[Sea urchin]] erosion of calcium carbonate (CaCO<sub>3</sub>) at some reefs has been reported to occur at annual rates exceeding 20 kg/m².
 
    
 
    
Fish also erode coral while eating [[algae]]. [[Parrotfish]] cause a great deal of bioerosion, due to their well developed jaw muscle and tooth armature, and a [[pharyngeal mill]], which grinds up ingested material into sand-sized particles. Bioerosion of reef [[calcium carbonate]] by parrotfish can range from 1017.7±186.3 kg yr-¹ (0.41±0.07 m³ yr-¹) for [[Chlorurus gibbus]] and 23.6±3.4 kg yr-¹ (9.7 10-³±1.3 10-³ m²yr-¹) for [[Chlorurus sordidus]] (Bellwood, 1995).
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Fish also erode coral while eating [[algae]]. [[Parrotfish]] cause a great deal of bioerosion, as a result of their well developed jaw muscles and tooth armature, and a [[pharyngeal mill]] that grinds up ingested material into sand-sized particles.<ref>Bioerosion of reef [[calcium carbonate]] by parrotfish can range from 1017.7±186.3 kg yr-¹ (0.41±0.07 m³ yr-¹) for [[Chlorurus gibbus]] and 23.6±3.4 kg yr-¹ (9.7 10-³±1.3 10-³ m²yr-¹) for [[Chlorurus sordidus]]. D.R. Bellwood, "Direct estimate of bioerosion by two parrotfish species, Chlorurus gibbus and C. sordidus, on the Great Barrier Reef, Australia." ''Marine Biology''  121(3)(1995): 419-429.</ref>.
  
 
==Tectonic effects of erosion==
 
==Tectonic effects of erosion==
The removal by erosion of large amounts of rock, from a particular region and its deposition elsewhere, can result in a lightening of the load on the lower crust and mantle. This can cause [[tectonic uplift|tectonic]] or [[isostasy|isostatic uplift]] in the region. Research undertaken since the early 1990´s suggests that the spatial distribution of erosion at the surface of an '''orogen''' can exert a key influence on its growth and its final internal structure.
+
 
 +
When erosion involves the removal of large amounts of rock from a particular region and its deposition elsewhere, it can lighten the load on the lower crust and mantle. This can cause [[tectonic uplift|tectonic]] or [[isostasy|isostatic uplift]] in the region. Research undertaken since the early 1990s suggests that the spatial distribution of erosion at the surface of an orogen (mountain-forming belt of rock along a tectonic plate) can exert a key influence on its development and its final internal structure.
  
 
== Erosion control ==
 
== Erosion control ==
 
 
[[Image:TerracesBuffers.JPG|thumb|right|250px|Terraces, conservation tillage, and conservation buffers save soil and improve water quality on this Iowa farm. [Photo by Lynn Betts, 1999, USDA Natural Resources Conservation Service.]]]
 
[[Image:TerracesBuffers.JPG|thumb|right|250px|Terraces, conservation tillage, and conservation buffers save soil and improve water quality on this Iowa farm. [Photo by Lynn Betts, 1999, USDA Natural Resources Conservation Service.]]]
  
'''Erosion control''' is the practice of preventing or controlling wind or water [[erosion]] in [[agriculture]], [[land development]]*, and [[construction]]. This usually involves the creation of some sort of physical barrier, such as vegetation or rock, to absorb some of the energy of the wind or water that is causing the erosion.
+
'''Erosion control''' is the practice of preventing or controlling wind or water [[erosion]] in [[agriculture]], [[land development]], and [[construction]]. It usually involves the creation of some type of physical barrier, such as vegetation or rock, to absorb some of the energy of the wind or water causing the erosion. Some examples of erosion control methods are given below.
 
 
Examples of some erosion control methods include:
 
*[[conservation tillage]] is used as a way to conserve soil and water resources as well as mitigate the problems of erosion by tilling strips of soil for planting new crops and maintaining untilled portions of the land to serve as anchors for the soil <"Sustainable Practices For Vegetable Production in the South: Conservation Tillage." NY State University, October 2001. http://www.cals.ncsu.edu/sustainable/peet/tillage/tillage.html>
 
*[[contour plowing]] is a farming technique where plowing is patterned according to the contours of a sloped region to prevent run off and allow water retension in the land <copied from Wiki Contour plowing>
 
*[[terrace (agriculture)|terracing]] is a technique used in agriculture to aid in planting along sleep slopes breaking the slopes down into a series of slopes that are shorter and less steep, slowing down runoff and preventing water erosion <"Backyard Conservation Tip Sheet: Terracing." NRCS (Natural Resources Conservation Service. http://www.nrcs.usda.gov/Feature/backyard/terrac.html>
 
*[[cover crop]]s are any surface crops that are planted annually, biennially, or perennially, in conjunction with other crops or alone, and last during a part or over the course of an entire year, preventing the erosion of the soil by wind or water. They are used as a means of sustainable cropping, prevent weeds, and reduce the leaching of nutrients from the soil <Sullivan, Preston. "Overview of Cover Crops and Green Manures: Fundamentals of Sustainable Agriculture." National Sustainable Agriculture Information Service. ATTRA, 2003. http://attra.ncat.org/attra-pub/covercrop.html>
 
*[[gabion]]s prevent shoreline erosion by creating a strong barrier of rock between fast flowing waves and the shore, resisting the impact of the water on the land and dissipating the energy of the waves against the shore <from wiki Gabions and riprap articles>
 
*[[riprap]] is rock or other material that works in the reduction of shoreline erosion, and are constructed into gabion barriers. The shape of the rocks make an impact on their overall effectiveness against wave attack on them <copied from wiki riprap>
 
*[[hydroseeding]], also referred to as hydromulching, is used as a quick, economical, and effective means of ground cover by planting grass in large areas of exposed soil. The seeds are mixed together in a slurry of mulch and other essential fertilizers and sprayed uniformly across the soil, creating a favorable, nutrient rich environment for the germination and establishment of grass seedlings into the soil <"Hydromulching and hydroseeding defined: a grass planting process." Turfmaker, 2000. http://www.turfmaker.com/Information_Questions_and_Feed/Request_Process/The_Processes_/the_processes_.html> <Copied also from Wiki Hydroseeding>
 
*[[mulching]] is an agricultural process that covers the soil and serves to protect it from water erosion as well as maintain moisture in the soil <copied from Wiki mulch> 
 
*[[reforestation]] is instrumental in mitigating soil erosion through the restoration of forest and woodland areas that were previously deforested, or stripped of vegetation <copied from Wiki reforestation>
 
*[[riparian strips]] are regions along a river bank that serve as natural controls against runoff and soil erosion by stabilizing the soil. They are characterized by the vegetation that inhabit these marginal areas <copied from Wiki riparian zones>
 
*[[strip farming]] is used in steep sloping areas to prevent soil erosion. In strip farming, alternating row and more tightly grown crops are sown beside one another, to stabilize the soil and enhance water retention and percolation <copied from Wiki Strip farming>
 
*[[vegetated waterways]] are channels developed to stabilize and direct runoff in such a way as to reduce erosion "Vegetated Waterways." Resource Conservation District of Monterey County. RCDMC, 2005 http://www.rcdmonterey.org/Growers_Ranchers_Landowners/Planning_Design/vegetated_waterway.html>
 
*[[wattle (construction)]]is an organization of interwoven plant materials used as a fence, preventing sedimentation by runoff and erosion <From Wiki Wattle and daub>
 
*[[windbreak]]s, also known as shelterbelts, involve the planting of trees or shrubs along distinct parameters or in an arranged pattern to reduce erosion by wind <From Wiki Windbreak>
 
  
== Terminology ==
+
*'''[[Conservation tillage]]:''' It is used as a way to conserve soil and water resources as well as to mitigate the problems of erosion by tilling strips of soil for planting new crops and maintaining untilled portions of the land to serve as anchors for the soil.<ref>Mary Peet, ''[http://www.cals.ncsu.edu/sustainable/peet/tillage/tillage.html "Sustainable Practices For Vegetable Production in the South: Conservation Tillage"].'' New York State University, October 2001. Retrieved May 24, 2008.</ref>
 +
*'''[[Contour plowing]]:''' In this farming technique, plowing is patterned according to the contours of a sloped region to prevent runoff and allow water retention in the land<ref>copied from Wiki Contour plowing</ref>
 +
*'''[[Terrace (agriculture)|Terracing]]:''' This agricultural technique aids in planting along sleep slopes by breaking each slope into a series of slopes that are shorter and less steep, slowing down runoff and preventing water erosion.<ref>[http://www.nrcs.usda.gov/Feature/backyard/terrac.html "Backyard Conservation Tip Sheet: Terracing"] Natural Resources Conservation Service. ''NRCS.USDA.gov''.Retrieved May 24, 2008. </ref>
 +
*'''[[Cover crop]]s:''' These are any surface crops planted annually, biennially, or perennially, in conjunction with other crops or alone. They last through a part of a year or even an entire year, preventing erosion of the soil by wind and water. Cover crops are used as a means of sustainable cropping, preventing weeds, and reducing the leaching of nutrients from the soil.<ref>Preston Sullivan, [http://attra.ncat.org/attra-pub/covercrop.html Sullivan, Preston, "Overview of Cover Crops and Green Manures: Fundamentals of Sustainable Agriculture"] National Sustainable Agriculture Information Service. ''ATTRA'', 2003. Retrieved May 24, 2008.</ref>
 +
*'''[[Riprap]]''' and '''[[gabion]]s''': Riprap consists of rock or other material placed along a shore. It reduces shoreline erosion by protecting the land from the full impact of fast-flowing waves. Caged riprap structures are known as gabions.
 +
*'''[[Hydroseeding]]:''' Also referred to as hydromulching, it is a quick, economical, and effective means of establishing ground cover by planting grass in large areas of exposed soil. The seeds are mixed together in a slurry of mulch and other essential fertilizers and sprayed uniformly across the soil, creating a favorable, nutrient rich environment for the germination and establishment of grass seedlings into the soil.
 +
*'''[[Mulching]]:''' It is a process that uses mulch to cover and protect the soil from water erosion and to maintain moisture in the soil.
 +
*'''[[Reforestation]]:''' This method of mitigating soil erosion consists of restoring forests and woodlands in areas that were once deforested or stripped of vegetation.
 +
*'''[[Riparian strips]]:''' These are regions along a riverbank characterized by the growth of vegetation. They stabilize the soil and serve as natural controls against runoff and soil erosion.
 +
*'''[[Strip farming]]:''' It is used in steep, sloping areas to prevent soil erosion. In strip farming, alternating row and more tightly grown crops are sown next to one another, to stabilize the soil and enhance water retention and percolation.
 +
*'''[[Vegetated waterways]]:''' These are channels developed to stabilize and direct runoff in such a way as to reduce erosion.<ref>[http://www.rcdmonterey.org/Growers_Ranchers_Landowners/Planning_Design/vegetated_waterway.html  "Vegetated Waterways"] Resource Conservation District of Monterey County, 2005. Retrieved May 24, 2008.</ref>
 +
*'''[[Wattle (construction)]]:''' It is an organization of interwoven plant materials used as a fence, preventing sedimentation by runoff and erosion.
 +
*'''[[Windbreak]]s:''' Also known as shelterbelts, they involve the planting of trees or shrubs along distinct parameters or in an arranged pattern to reduce erosion by wind.
  
===Origin of term===
+
== Origin and alternative meanings of "erosion" ==
  
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 [[ulcer]]s 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
+
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 [[ulcer]]s developed in the [[mouth]]. By 1774, "erosion" was used outside of medical subjects. [[Oliver Goldsmith]] employed the term in the more contemporary geological context, in his book ''Natural History,'' with the words "Bounds are thus put to the erosion of the earth by water."
:"''Bounds are thus put to the erosion of the earth by water''."
 
  
===Usage in 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 nonabrasive fluid mixtures. [[Cavitation]] is one example.
  
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.
+
The concept of erosion is commonly employed by [[analogy]] to various forms of perceived or real breakdown, removal (such as 'erosion of boundaries'), "leveling out," or even the decline of anything from [[morality]] to [[Indigenous peoples|indigenous cultures]]. It is a common [[trope]] of the English language to describe ''erosion'' as the gradual, organic transformation of something considered distinct, more complex, harder to pronounce, or more refined into something indistinct, less complex, easier to pronounce, or (disparagingly) less refined.
 
 
===Figurative use===
 
 
 
The concept of erosion is commonly employed by [[analogy]] to various forms of perceived or real breakdown, removal (such as "erosion of boundaries"), "leveling out", or even the decline of anything from [[morality|morals]] to [[Indigenous peoples|indigenous cultures]]. It is a common [[trope]] of the English language to describe ''erosion'' as 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.
 
  
 
== See also ==
 
== See also ==
  
*[[Badland]]
+
*[[Ecology]]
*[[Biorhexistasy]]
+
*[[Environmental science]]
*[[Groundwater sapping]]
+
*[[Earth science]]
*[[Erosion prediction]]
+
*[[Soil]]
*[[Riparian strips]]
 
*[[Surface runoff]]
 
 
*[[Weathering]]
 
*[[Weathering]]
  
== Footnotes ==
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== Notes ==
 
<references/>
 
<references/>
<!--See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for an explanation of how to generate
 
footnotes using the <ref(erences/)> tags—>
 
  
 
==References==
 
==References==
  
* World Bank, 2001: ''China: Air, Land, and Water.''
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* Alt, David. ''Glacial Lake Missoula & its Humongous Floods.'' Mountain Press Publishing Company, 2001. ISBN 0878424156
*[http://eusoils.jrc.it/ESDB_Archive/pesera/pesera_cd/index.htm Pan European Soil Erosion Assessment]
+
* ''China: Air, Land, and Water: Environmental Priorities for a New Millennium'' Washington, DC: The World Bank, 2001. ISBN 0821349376.
* Belwood, D. R. (1995). "Direct estimate of bioerosion by two parrotfish species, ''Chlorurus gibbus'' and ''C. sordidus'', on the Great Barrier Reef, Australia." ''Marine Biology'', 121(3), 419-429. [http://www.springerlink.com/app/home/contribution.asp?wasp=062adee92a994ec496adcb3289502841&referrer=parent&backto=issue,3,19;journal,24,460;linkingpublicationresults,1:400441,1]
+
* Belwood, D. R. "Direct estimate of bioerosion by two parrotfish species, ''Chlorurus gibbus'' and ''C. sordidus'', on the Great Barrier Reef, Australia." ''Marine Biology'', vol. 121(3) (1995): 419-429. [http://www.springerlink.com/app/home/contribution.asp?wasp=062adee92a994ec496adcb3289502841&referrer=parent&backto=issue,3,19;journal,24,460;linkingpublicationresults,1:400441,1]
 +
* Morgan, R.P.C. (ed.) ''Soil Erosion and Its Control''. Van Nostrand Reinhold Science Series. New York: Van Nostrand Reinhold Company, 1986. ISBN 0442264410.
 +
* Rapp, Anders. "Soil Erosion and Sedimentation in Tanzania and Lesotho." ''Ambio'' 4 (4) (1975): 154-163. Royal Swedish Academy of Sciences.
  
 
== External links ==
 
== External links ==
 
+
All links retrieved August 16, 2017.
*[http://www.eoearth.org/article/Soil_erosion_and_deposition Encyclopedia of Earth: Soil erosion and deposition]
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*Michael Pidwirny [http://editors.eol.org/eoearth/wiki/Soil_erosion_and_deposition Soil erosion and deposition] ''The Encyclopedia of Earth''.
*[http://www.whoi.edu/institutes/coi/viewTopic.do?o=read&id=21 Coastal Erosion Information from the Coastal Ocean Institute], [[Woods Hole Oceanographic Institution]]*
 
 
*[http://www.ieca.org International Erosion Control Association]
 
*[http://www.ieca.org International Erosion Control Association]
 
*[http://www.erosioncontrol.com Erosion Control] - a trade magazine for the erosion control industry
 
*[http://www.erosioncontrol.com Erosion Control] - a trade magazine for the erosion control industry
*[http://www.dirttimetv.com Dirt Time] - A Television Series dedicated completely to the Erosion & Sediment Control Industry
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[[Category:Physical sciences]]
 
[[Category:Physical sciences]]
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[[Category:Environmental science]]
 
[[Category:Earth sciences]]
 
[[Category:Earth sciences]]
  
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Revision as of 11:21, 19 February 2022

Severe soil erosion in a wheat field near Washington State University, U.S.A.

In geology and environmental science, erosion is the displacement of solids (soil, mud, rock and other particles) by the agents of wind, water, ice, or living organisms, or by down-slope movement in response to gravity. Erosion needs to be distinguished from weathering, although the two processes may be concurrent. Weathering refers to the decomposition of rock and minerals through processes involving no movement, that is, no physical removal of material.

Erosion is a natural process, moving material and nutrients from one place to another and converting rock into soil. Thus a certain degree of erosion is healthy for the ecosystem. Excessive erosion, however, can damage the ecosystem, such as by increased water sedimentation or the outright loss of soil.

In many places, erosion is heightened by human land use. Poor land-use practices include deforestation, overgrazing, unmanaged construction activity, and road or trail building. On the other hand, improved land-use practices can limit erosion, by techniques such as tree planting and terrace-building, or leveling of the land interrupting steep slopes.[1]

Causes

Erosion is governed by a combination of factors, including the amount and intensity of precipitation (particularly rain), soil texture, gradient of the slope, ground cover (from vegetation, rocks, and so forth), and land use. Of these, the main agent of erosion is rainfall.

In general, if one compares areas with the same degree of vegetative cover, erosion tends to be higher in areas with high-intensity precipitation, sandy or silty soils, and steep slopes. On the other hand, there is less erosion of soils with a higher content of clay, situated along lower slope gradients, and receiving less intense precipitation.

Among the factors listed above, the one most likely to change over time is the amount and type of ground cover. When fires burn an area, or when vegetation is removed during timber operations or house or road construction, a soil's susceptibility to erosion is greatly increased. Road construction can increase the rate of erosion because, in addition to removing vegetative ground cover, it can significantly alter drainage patterns. However, erosion is minimized if the road has a lot of rock and is "hydrologically invisible," that is, the water flows off the road as quickly as possible, mimicking natural drainage patterns.

Bank erosion started by four-wheeler, all-terrain vehicles in Yauhanna, South Carolina.

Changes in the type of vegetation in an area can also affect erosion rates. Different kinds of vegetation have an effect on the rates of infiltration of rain into the soil. Forested areas can take up water at higher rates, so precipitation there results in less surface runoff, and subsequently, less erosion of surface materials. In these areas, much of the water goes into subsurface flows, which are generally less erosive. Leaf litter and low shrubs also contribute to the high infiltration rates of forested systems, and removing them can lead to an increase in erosion rates. Leaf litter also shelters the soil from the impact of falling raindrops, which is a significant agent of erosion. Vegetation can also change the speed of surface runoff flows, so the presence of grasses and shrubs plays an important role in this respect as well.

Many human activities, such as logging and heavy grazing by livestock, can reduce an area's vegetation, making the soil more susceptible to increased erosion. One of the main causes of erosive soil loss in the year 2006 was the result of "slash-and-burn" treatment of tropical forests. When the total ground surface is stripped of vegetation and seared of all living organisms, the upper soils are vulnerable to erosion by both wind and water. In a number of regions of the world, entire sectors of a country have been rendered unproductive. For example, on the Madagascar high central plateau, constituting approximately 10 percent of that country's land area, virtually the entire landscape is sterile of vegetation, with gully erosive furrows scattered along the landscape—typically more than 50 meters deep and one kilometer wide. Shifting cultivation is a farming system that sometimes incorporates the slash-and-burn method in some regions of the world.

When land is overused by human and animal activities, there can be mechanical erosion as well as removal of vegetation, leading to erosion. In the case of animals, one sees this effect primarily with large herd stampedes, such as the Blue Wildebeest on the Serengeti plain. Even in this case, there are broader material benefits to the ecosystem, such as continuing the survival of grasslands indigenous to that region. This effect may be viewed as a problem only when there is a significant imbalance or overpopulation of one species.

In the case of human use, the effects are also generally linked to overpopulation. For example, when large numbers of hikers use the same trails, or when there is extensive off-roading by vehicles, erosive effects often follow, arising from vegetation removal and furrowing of the soil. These effects can also accumulate from a variety of outdoor human activities, again arising from too many people using a finite land resource.

One of the most serious and long-running water erosion problems worldwide is in China, around the middle reaches of the Yellow River and the upper reaches of the Yangtze River. From the Yellow River, over 1.6 billion tons of sediment flow into the ocean each year. The sediment originates primarily from water erosion in the Loess Plateau region of northwest China.

Erosion processes

A heavily eroded roadside near Ciudad Colon, Costa Rica.

Gravity erosion

"Mass wasting" is the down-slope movement of rock and sediments, caused mainly by the force of gravity. Mass wasting is an important part of the erosion process, as it moves material from higher elevations to lower elevations, where transporting agents like streams and glaciers can pick up the material and move it further down. Mass-wasting processes occur continuously on all slopes. Some of these processes take place very slowly; others occur very suddenly, often with disastrous results.

Any perceptible down-slope movement of rock or sediment is often referred to in general terms as a "landslide." There are, however, more detailed ways of classifying landslides, reflecting the mechanisms responsible for the movement and the velocity at which the movement occurs. One visible topographical manifestation of a very slow type of landslide is a scree slope.

"Slumping" is a form of mass-wasting in which consolidated materials or rock layers move together a short distance down a slope. Slumping happens on steep hillsides, and often with materials like clay that, once released, may move rapidly downhill. The area left behind by the moving material often shows a spoon-shaped depression. In some cases, the slump is caused by water beneath the slope, weakening layers of rock above it. In many cases, it is simply the result of poor engineering along highways, where it is a regular occurrence.[2]

"Surface creep" is the slow movement of soil and rock debris by gravity. It is usually not perceptible, except through extended observation. This term, however, is also used to describe the rolling of dislodged soil particles (0.5 to 1.0 mm in diameter) by wind along the soil surface.

A nearly perfect sphere of granite, in Trégastel, Brittany.

Water erosion

"Splash erosion" is the detachment and airborne movement of small soil particles, caused by the impact of raindrops falling on the soil. "Sheet erosion" is the result of heavy rain on bare soil, where water flows as a sheet down a gradient, carrying soil particles. In any area where precipitation rates exceed the absorption and infiltration rates into the soil, runoff occurs. Surface runoff turbulence can often cause more erosion than the initial raindrop impact. "Gully erosion" occurs in places where water flows along a linear depression, eroding a trench or gully (a furrow in the soil that is more than one meter deep).[3]

"Valley" or "stream erosion" takes place 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-shaped 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 (twists and turns) across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood, when greater amounts and faster-moving water is available to carry a larger sediment load. In such processes, erosion is caused not only by water but also by suspended abrasive particles, such as pebbles and boulders, as they traverse the surface.

At extremely high rates of flow, kolks (underwater 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 that resulted from glacial activity at Glacial Lake Missoula, which created the channeled scablands in the Columbia basin region of eastern Washington state.[4] [5]

Shoreline erosion

Wave-cut platform caused by erosion of cliffs by the sea, at Southerndown in South Wales.
File:Coastal Erosion.jpg
Coastal erosion at Happisburgh, Norfolk, England.

Shoreline erosion, on both exposed and sheltered coasts, occurs primarily through the action of currents and waves, but sea level (tidal) changes can also play a role. When the sheer energy of a wave hitting a cliff or rock breaks pieces off, this is known as wave pounding. "Abrasion" or "corrasion" is caused by waves launching seaload at the cliff. It is the most effective and rapid form of shoreline erosion. (Corrasion should not to be confused with corrosion, or the dissolving of rock by carbonic acid in seawater. Limestone cliffs are particularly vulnerable to this type of erosion). Finally, "attrition" is where particles/seaload carried by the waves are worn down, as they strike one another and rock surfaces like cliffs, making the material easier to wash away.

Sediment is transported along the coast in the direction of the prevailing current (known as "longshore drift"). Erosion occurs when the uptake of new sediment by the upcurrent is less than the amount being carried away. 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 buildup of eroded material occurs, forming a long, narrow bank (or "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 impact different parts of the shore.

Ice erosion

Ice erosion is caused by the movement of ice, typically in the form of glaciers. As glaciers scrape down slopes, they break up rock and transport it, leaving moraines (accumulation of rock debris), drumlins (elongated hills or ridges), and glacial erratics (pieces of glacial residue) in their wake, typically at the glacial terminus or during glacial retreat.[6] [7]

"Ice wedging" is the weathering process in which water trapped in tiny cracks of rock freezes and expands, breaking the rock, allowing for gravity erosion on steep slopes. The scree that 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 that are 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 wind. The wind causes dust particles to be lifted up, where they can be moved to other regions. Wind erosion generally occurs in areas with little or no vegetation, often in places where there is insufficient rainfall to support vegetation. An example is the formation of sand dunes on a beach or in a desert. Farmers often plant windbreaks to reduce wind erosion. This includes the planting of trees, shrubs, or other vegetation, usually perpendicular (or nearly so) to the principal wind direction.

Bioerosion

Bioerosion involves the erosion of hard ocean substrates by living organisms, utilizing a number of mechanisms. It can be caused by mollusks, polychaete worms, sponges, crustaceans, echinoids, and fish. It can occur on coastlines and coral reefs, and on the hulls of ships. Mechanisms of bioerosion include biotic boring, drilling, rasping, and scraping.

Bioerosion of coral reefs generates the fine and white coral sand characteristic of tropical islands. The coral is converted to sand by internal bioeroders such as algae, fungi, bacteria, sponges (Clionidae), bivalves (Lithophaga), sipunculans (Aspidosiphon), and polychaetes (Eunicidae), generating extremely fine sediment (10 to 100 micrometers in diameter). External bioeroders include urchins (Diadema) and chitons (Acanthopleura). The combination of these internal and external bioeroders results in a great deal of erosion. Sea urchin erosion of calcium carbonate (CaCO3) at some reefs has been reported to occur at annual rates exceeding 20 kg/m².

Fish also erode coral while eating algae. Parrotfish cause a great deal of bioerosion, as a result of their well developed jaw muscles and tooth armature, and a pharyngeal mill that grinds up ingested material into sand-sized particles.[8].

Tectonic effects of erosion

When erosion involves the removal of large amounts of rock from a particular region and its deposition elsewhere, it can lighten the load on the lower crust and mantle. This can cause tectonic or isostatic uplift in the region. Research undertaken since the early 1990s suggests that the spatial distribution of erosion at the surface of an orogen (mountain-forming belt of rock along a tectonic plate) can exert a key influence on its development and its final internal structure.

Erosion control

Terraces, conservation tillage, and conservation buffers save soil and improve water quality on this Iowa farm. [Photo by Lynn Betts, 1999, USDA Natural Resources Conservation Service.]

Erosion control is the practice of preventing or controlling wind or water erosion in agriculture, land development, and construction. It usually involves the creation of some type of physical barrier, such as vegetation or rock, to absorb some of the energy of the wind or water causing the erosion. Some examples of erosion control methods are given below.

  • Conservation tillage: It is used as a way to conserve soil and water resources as well as to mitigate the problems of erosion by tilling strips of soil for planting new crops and maintaining untilled portions of the land to serve as anchors for the soil.[9]
  • Contour plowing: In this farming technique, plowing is patterned according to the contours of a sloped region to prevent runoff and allow water retention in the land[10]
  • Terracing: This agricultural technique aids in planting along sleep slopes by breaking each slope into a series of slopes that are shorter and less steep, slowing down runoff and preventing water erosion.[11]
  • Cover crops: These are any surface crops planted annually, biennially, or perennially, in conjunction with other crops or alone. They last through a part of a year or even an entire year, preventing erosion of the soil by wind and water. Cover crops are used as a means of sustainable cropping, preventing weeds, and reducing the leaching of nutrients from the soil.[12]
  • Riprap and gabions: Riprap consists of rock or other material placed along a shore. It reduces shoreline erosion by protecting the land from the full impact of fast-flowing waves. Caged riprap structures are known as gabions.
  • Hydroseeding: Also referred to as hydromulching, it is a quick, economical, and effective means of establishing ground cover by planting grass in large areas of exposed soil. The seeds are mixed together in a slurry of mulch and other essential fertilizers and sprayed uniformly across the soil, creating a favorable, nutrient rich environment for the germination and establishment of grass seedlings into the soil.
  • Mulching: It is a process that uses mulch to cover and protect the soil from water erosion and to maintain moisture in the soil.
  • Reforestation: This method of mitigating soil erosion consists of restoring forests and woodlands in areas that were once deforested or stripped of vegetation.
  • Riparian strips: These are regions along a riverbank characterized by the growth of vegetation. They stabilize the soil and serve as natural controls against runoff and soil erosion.
  • Strip farming: It is used in steep, sloping areas to prevent soil erosion. In strip farming, alternating row and more tightly grown crops are sown next to one another, to stabilize the soil and enhance water retention and percolation.
  • Vegetated waterways: These are channels developed to stabilize and direct runoff in such a way as to reduce erosion.[13]
  • Wattle (construction): It is an organization of interwoven plant materials used as a fence, preventing sedimentation by runoff and erosion.
  • Windbreaks: Also known as shelterbelts, they involve the planting of trees or shrubs along distinct parameters or in an arranged pattern to reduce erosion by wind.

Origin and alternative meanings of "erosion"

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 of medical subjects. Oliver Goldsmith employed the term in the more contemporary geological context, in his book Natural History, with the words "Bounds are thus put to the erosion of the earth by water."

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 nonabrasive fluid mixtures. Cavitation is one example.

The concept of erosion is commonly employed by analogy to various forms of perceived or real breakdown, removal (such as 'erosion of boundaries'), "leveling out," or even the decline of anything from morality to indigenous cultures. It is a common trope of the English language to describe erosion as the gradual, organic transformation of something considered distinct, more complex, harder to pronounce, or more refined into something indistinct, less complex, easier to pronounce, or (disparagingly) less refined.

See also

Notes

  1. "Terrace" The Free Dictionary by Farlex.
  2. Parts adapted from 'Slump' in Wikipedia.
  3. Anders Rapp, "Soil Erosion and Sedimentation in Tanzania and Lesotho." Ambio 4 (4): 154-163. Royal Swedish Academy of Sciences, 1975.
  4. David Alt. Glacial Lake Missoula & its Humongous Floods. (Mountain Press Publishing Company, 2001. ISBN 0878424156).
  5. Lyn Topinka, Topinka, Lyn, "Glacial Lake Missoula and the Missoula Floods". USGS/Cascades Volcano Observatory, Vancouver, Washington, July 5, 2002. Accessed on November 28, 2006.
  6. "Drumlin" The American Heritage Dictionary of the English Language, Fourth Ed. (Houghton Mifflin Company, 2000).Retrieved May 24, 2008.
  7. "Moraine". The American Heritage Dictionary of the English Language, Fourth Ed. (Houghton Mifflin Company, 2000). Retrieved May 24, 2008.
  8. Bioerosion of reef calcium carbonate by parrotfish can range from 1017.7±186.3 kg yr-¹ (0.41±0.07 m³ yr-¹) for Chlorurus gibbus and 23.6±3.4 kg yr-¹ (9.7 10-³±1.3 10-³ m²yr-¹) for Chlorurus sordidus. D.R. Bellwood, "Direct estimate of bioerosion by two parrotfish species, Chlorurus gibbus and C. sordidus, on the Great Barrier Reef, Australia." Marine Biology 121(3)(1995): 419-429.
  9. Mary Peet, "Sustainable Practices For Vegetable Production in the South: Conservation Tillage". New York State University, October 2001. Retrieved May 24, 2008.
  10. copied from Wiki Contour plowing
  11. "Backyard Conservation Tip Sheet: Terracing" Natural Resources Conservation Service. NRCS.USDA.gov.Retrieved May 24, 2008.
  12. Preston Sullivan, Sullivan, Preston, "Overview of Cover Crops and Green Manures: Fundamentals of Sustainable Agriculture" National Sustainable Agriculture Information Service. ATTRA, 2003. Retrieved May 24, 2008.
  13. "Vegetated Waterways" Resource Conservation District of Monterey County, 2005. Retrieved May 24, 2008.

References
ISBN links support NWE through referral fees

  • Alt, David. Glacial Lake Missoula & its Humongous Floods. Mountain Press Publishing Company, 2001. ISBN 0878424156
  • China: Air, Land, and Water: Environmental Priorities for a New Millennium Washington, DC: The World Bank, 2001. ISBN 0821349376.
  • Belwood, D. R. "Direct estimate of bioerosion by two parrotfish species, Chlorurus gibbus and C. sordidus, on the Great Barrier Reef, Australia." Marine Biology, vol. 121(3) (1995): 419-429. [1]
  • Morgan, R.P.C. (ed.) Soil Erosion and Its Control. Van Nostrand Reinhold Science Series. New York: Van Nostrand Reinhold Company, 1986. ISBN 0442264410.
  • Rapp, Anders. "Soil Erosion and Sedimentation in Tanzania and Lesotho." Ambio 4 (4) (1975): 154-163. Royal Swedish Academy of Sciences.

External links

All links retrieved August 16, 2017.

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