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| {{about||morphological image processing operations|Erosion (morphology)|use of in dermatopathology|Erosion (dermatopathology)}}
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| [[Image:KharazaArch.jpg|thumb|thumb|A [[natural arch]] produced by the erosion of differentially weathered rock in Jebel Kharaz, [[Jordan]].]]
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| '''Erosion''' is the process by which soil and rock are removed from the Earth's surface by exogenic processes such as wind or water flow, and then [[sediment transport|transported]] and [[deposition (geology)|deposited]] in other locations.
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| While erosion is a natural process, human activities have increased by 10-40 times the rate at which erosion is occurring globally. Excessive erosion causes problems such as [[desertification]], decreases in agricultural productivity due to land degradation, [[sediment]]ation of waterways, and [[ecological collapse]] due to loss of the nutrient rich upper [[soil horizon|soil layers]]. Water and wind erosion are now the two primary causes of [[land degradation]]; combined, they are responsible for 84% of degraded acreage, making excessive erosion one of the most significant global environmental problems.<ref name="Springer">{{cite book|authors=Blanco, Humberto & Lal, Rattan|chapter=Soil and water conservation|title=Principles of Soil Conservation and Management|publisher=Springer|year=2010|isbn=978-90-481-8529-0|page=2|url=http://books.google.com/books?id=Wj3690PbDY0C&pg=PA2}}</ref><ref name="toy-2002-p1" />
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| [[Industrial agriculture]], [[deforestation]], [[roads]], anthropogenic [[climate change]] and [[urban sprawl]] are amongst the most significant human activities in regard to their effect on stimulating erosion.<ref>{{Cite book|author=Julien, Pierre Y.|title=Erosion and Sedimentation|publisher=Cambridge University Press|year=2010|isbn=978-0-521-53737-7|page=1|url=http://books.google.com/books?id=Gv72uiVmWEYC&pg=PA1}}</ref> However, there are many [[Erosion#Prevention and remediation|prevention and remediation]] practices that can curtail or limit erosion of denuded soils.
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| ==Physical processes==
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| ===Rainfall===
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| [[File:Rummu aherainemägi2.jpg|thumb|A [[spoil tip]] covered in rills and gullies due to erosion processes caused by rainfall. [[Rummu]], [[Estonia]].]]
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| There are four primary types of erosion that occur as a direct result of rainfall: ''splash erosion'', ''sheet erosion'', ''rill erosion'', and ''gully erosion''. Splash erosion is generally seen as the first and least severe stage in the soil erosion process, which is followed by sheet erosion, then rill erosion and finally gully erosion (the most severe of the four).<ref>{{cite book|authors=Toy, Terrence J. et al|title=Soil Erosion: Processes, Prediction, Measurement, and Control|publisher=John Wiley & Sons|year=2002|isbn=978-0-471-38369-7|pages=60–61|url=http://books.google.com/books?id=7YBaKZ-28j0C&pg=PA60}}</ref><ref>{{cite book|author= Zachar, Dušan|chapter=Classification of soil erosion|title=Soil Erosion|volume=Vol. 10|publisher=Elsevier|year=1982|isbn=978-0-444-99725-8|page=48|url=http://books.google.com/books?id=o8ny2dUkpM8C&pg=PA48}}</ref>
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| In splash erosion, the impact of a falling raindrop creates a small crater in the soil,<ref name="Fig. 4">{{cite news|author=see Fig. 4 in Obreschkow|title=Confined Shocks inside Isolated Liquid Volumes - A New Path of Erosion?|publisher=Physics of Fluids|year=2011|url=http://arxiv.org/abs/1109.3175}}</ref> ejecting soil particles. The distance these soil particles travel can be as much as two feet (0.6 m) vertically and five feet (1.5 m) horizontally on level ground. Once the rate of rainfall is faster than the rate of infiltration into the soil, [[surface runoff]] occurs and carries the loosened soil particles down the slope.<ref name="FAO-1965-pp23-25">{{cite book|author=Food and Agriculture Organization|chapter=Types of erosion damage|title=Soil Erosion by Water: Some Measures for Its Control on Cultivated Lands|publisher=United Nations|year=1965|isbn=978-92-5-100474-6|pages=23–25|url=http://books.google.com/books?id=6KeL3ix6ZqQC&pg=PA23}}</ref>
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| ''Sheet erosion'' is the transport of loosened soil particles by overland flow.<ref name="FAO-1965-pp23-25" />
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| ''[[Rill]] erosion'' refers to the development of small, [[ephemeral]] concentrated flow paths which function as both sediment source and [[sediment]] delivery systems for erosion on hillslopes. Generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically of the order of a few centimeters or less (around an inch) and slopes may be quite steep. This means that rills exhibit [[hydraulic]] physics very different from water flowing through the deeper, wider channels of streams and rivers.{{Citation needed|date=April 2012}}
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| {{Anchor|gully erosion|ephemeral gully erosion}}
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| ''Gully erosion'' occurs when runoff water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow, removing soil to a considerable depth.<ref>{{cite book|authors=Poeson, Jean et al.|chapter=Gully erosion in Europe|editors=Boardman, John & Poeson, Jean|title=Soil Erosion in Europe|publisher=John Wiley & Sons|year=2007|isbn=978-0-470-85911-7|pages=516–519|url=http://books.google.com/books?id=vvOFRskFunwC&pg=PA516}}</ref><ref>{{cite book|authors=Poeson, Jean et al.|chapter=Gully erosion in dryland environments|editors=Bull, Louise J. & Kirby, M.J.|title=Dryland Rivers: Hydrology and Geomorphology of Semi-Arid Channels|publisher=John Wiley & Sons|year=2002|isbn=978-0-471-49123-1|url=http://books.google.com/books?id=qjHoYZXQee0C&pg=PA229}}</ref><ref>{{cite book|authors=Borah, Deva K. et al|chapter=Watershed sediment yield|editor=Garcia, Marcelo H.|title=Sedimentation Engineering: Processes, Measurements, Modeling, and Practice|publisher=ASCE Publishing|year=2008|isbn=978-0-7844-0814-8|page=828|url=http://books.google.com/books?id=1AsypwBUa_wC&pg=PA828}}</ref>
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| ===Rivers and streams===
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| {{Details|Hydraulic action|water's erosive ability}}
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| [[File:Dobbingstone Burn - geograph.org.uk - 1291882.jpg|thumb|Dobbingstone Burn, Scotland—This photo illustrates two different types of erosion affecting the same place. Valley erosion is occurring due to the flow of the stream, and the boulders and stones (and much of the soil) that are lying on the edges are [[glacial till]] that was left behind as ice age glaciers flowed over the terrain.]]
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| ''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, creating [[Head Cut (stream geomorphology)|head cuts]] and steep banks. 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 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, [[pebble]]s and [[boulder]]s can also act erosively as they traverse a surface, in a process known as ''traction''.<ref>Ritter, Michael E. (2006) [http://www4.uwsp.edu/geo/faculty/ritter/geog101/textbook/fluvial_systems/geologic_work_of_streams.html "Geologic Work of Streams"] ''The Physical Environment: an Introduction to Physical Geography'' University of Wisconsin, {{OCLC|79006225}}</ref>
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| ''Bank erosion'' is the wearing away of the banks of a [[stream]] or [[river]]. This is distinguished from changes on the bed of the watercourse, which is referred to as ''scour''. Erosion and [[River bank failure|changes in the form of river banks]] may be measured by inserting metal rods into the bank and marking the position of the bank surface along the rods at different times.<ref>{{Cite book |url=http://books.google.com/?id=_PJHw-hSKGgC&pg=PA113 |title=Stream hydrology: an introduction for ecologists |author=Nancy D. Gordon |chapter=Erosion and Scour |isbn=978-0-470-84357-4 |date=2004-06-01 |postscript=}}</ref>
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| ''Thermal erosion'' is the result of melting and weakening [[permafrost]] due to moving water.<ref name="nsidc_thermal">{{cite web|url=http://nsidc.org/cgi-bin/words/word.pl?thermal%20erosion|title=Thermal Erosion|work=NSIDC Glossary|publisher=[[National Snow and Ice Data Center]]|accessdate=21 December 2009|archiveurl = http://www.webcitation.org/5uLakeCcx |archivedate = 2010-11-18|deadurl=no}}</ref> It can occur both along rivers and at the coast. Rapid [[river channel migration]] observed in the [[Lena River]] of [[Siberia]] is due to thermal erosion, as these portions of the banks are composed of permafrost-cemented non-cohesive materials.<ref name="lena">{{cite journal|doi=10.1002/esp.592|title=Fluvial thermal erosion investigations along a rapidly eroding river bank: application to the Lena River (central Siberia)|year=2003|last1=Costard|first1=F.|last2=Dupeyrat|first2=L.|last3=Gautier|first3=E.|last4=Carey-Gailhardis|first4=E.|journal=Earth Surface Processes and Landforms|volume=28|page=1349|bibcode = 2003ESPL...28.1349C|issue=12 }}</ref> Much of this erosion occurs as the weakened banks fail in large slumps. Thermal erosion also affects the [[Arctic]] coast, where wave action and near-shore temperatures combine to undercut permafrost bluffs along the shoreline and cause them to fail. Annual erosion rates along a {{convert|100|km|mi|abbr=off|adj=on}} segment of the Beaufort Sea shoreline averaged {{convert|5.6|m|ft|abbr=off}} per year from 1955 to 2002.<ref name="jones_arctic">{{cite journal|last=Jones|first=B.M.|coauthors=Hinkel, K.M., Arp, C.D. and Eisner, W.R.|year=2008|title=Modern Erosion Rates and Loss of Coastal Features and Sites, Beaufort Sea Coastline, Alaska|journal=Arctic|publisher=[[Arctic Institute of North America]]|volume=61|issue=4|pages=361–372|url=http://arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/44/115}}</ref>
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| ===Coastal erosion===
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| {{main|Coastal erosion}}
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| {{See also|Beach evolution}}
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| [[File:Wavecut platform southerndown pano.jpg|thumb|[[Wave cut platform]] caused by erosion of cliffs by the sea, at [[Southerndown]] in South [[Wales]].]]
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| Shoreline erosion, which occurs on both exposed and sheltered coasts, primarily occurs through the action of currents and [[ocean surface wave|waves]] but sea level (tidal) change can also play a role.
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| ''[[Hydraulic action]]'' takes place when air in a joint is suddenly compressed by a wave closing the entrance of the joint. This then cracks it. ''[[Wave pounding]]'' is when the sheer energy of the wave hitting the cliff or rock breaks pieces off. ''[[abrasion (geology)|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. ''Attrition'' is where particles/seaload carried by the waves are worn down as they hit each other and the cliffs. This then makes the material easier to wash away. The material ends up as [[shingle beach|shingle]] and sand. Another significant source of erosion, particularly on carbonate coastlines, is the boring, scraping and grinding of organisms, a process termed ''[[bioerosion]]''.<ref>Glynn, Peter W. "Bioerosion and coral-reef growth: a dynamic balance." Life and death of coral reefs (1997): 68-95.</ref>
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| [[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 as a result of [[deposition (geology)|deposition]]. 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 (landform)|spit]]). [[Armor (hydrology)|Armoured]] beaches and submerged offshore [[shoal|sandbanks]] may also protect parts of a coastline from erosion. Over the years, as the shoals gradually shift, the erosion may be redirected to attack different parts of the shore.{{Citation needed|date=April 2012}}
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| ===Glaciers===
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| [[File:MorainesLakeLouise.JPG|thumb|Glacial [[moraines]] above [[Lake Louise, Alberta|Lake Louise]], in [[Alberta, Canada]].]]
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| [[Glacier]]s erode predominantly by three different processes: abrasion/scouring, [[Plucking (glaciation)|plucking]], and ice thrusting. In an abrasion process, debris in the basal ice scrapes along the bed, polishing and gouging the underlying rocks, similar to sandpaper on wood. Glaciers can also cause pieces of bedrock to crack off in the process of plucking. In ice thrusting, the glacier freezes to its bed, then as it surges forward, it moves large sheets of frozen sediment at the base along with the glacier. This method produced some of the many thousands of lake basins that dot the edge of the Canadian Shield. The erosion caused by glaciers worldwide has been shown to erode mountains so effectively that the term ''glacial buzz-saw'' has become widely used, which describes the limiting effect of glaciers on the height of mountain ranges.<ref name="ReferenceA">Stuart N. Thomson, Mark T. Brandon, Jonathan H. Tomkin, Peter W. Reiners, Cristián Vásquez, Nathaniel J. Wilson. Glaciation as a destructive and constructive control on mountain building. Nature, 2010; 467 (7313): 313 DOI: 10.1038/nature09365</ref> As mountains grow higher, they generally allow for more glacial activity (especially above the glacial equilibrium line altitude),<ref>Tomkin, J. H. & Roe, G. H. Climate and tectonic controls on glaciated critical-taper orogens. Earth Planet. Sci. Lett. 262, 385–397 (2007)</ref> which causes increased rates of erosion of the mountain, decreasing mass faster than [[isostatic rebound]] can add to the mountain.<ref>Mitchell, S. G. & Montgomery, D. R. Influence of a glacial buzzsaw on the height and morphology of the Cascade Range in central Washington State, USA. Quat. Res. 65, 96–107 (2006)</ref> This provides a good example of a [[negative feedback loop]]. Ongoing research is showing that while glaciers tend to decrease mountain size, in some areas, glaciers can actually reduce the rate of erosion, acting as a ''glacial armor''.<ref name="ReferenceA"/>
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| These processes, combined with erosion and transport by the water network beneath the glacier, leave [[moraine]]s, [[drumlin]]s, ground moraine (till), kames, kame deltas, moulins, and [[glacial erratic]]s in their wake, typically at the terminus or during [[Retreat of glaciers since 1850|glacier retreat]].{{Citation needed|date=April 2012}}
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| ===Floods===
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| At extremely high flows, [[kolk]]s, or [[vortex|vortices]] are formed by large volumes of rapidly rushing water. Kolks cause extreme local erosion, plucking bedrock and creating pothole-type geographical features called [[Rock-cut basin]]s. 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 (U.S. state)|Washington]].<ref>See, for example: {{cite book|author=Alt, David|title=Glacial Lake Missoula & its Humongous Floods
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| |publisher=Mountain Press|year=2001|isbn=978-0-87842-415-3|url=http://books.google.com/books?id=s4y3c8fxeEwC}}</ref>
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| ===Freezing and thawing===
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| Cold weather causes water trapped in tiny rock cracks to freeze and expand, breaking the rock into several pieces. 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 (soil) 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.{{Citation needed|date=April 2012}}
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| ===Wind erosion===
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| [[File:Im Salar de Uyuni.jpg|thumb|[[Árbol de Piedra]], a rock formation in the [[Altiplano]], [[Bolivia]] sculpted by wind erosion.]]
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| {{main|Aeolian processes}}
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| Wind erosion is a major [[geomorphological]] force, especially in [[arid region|arid]] and [[semi-arid region|semi-arid]] regions. It is also a major source of land degradation, evaporation, desertification, harmful airborne dust, and crop damage—especially after being increased far above natural rates by human activities such as [[deforestation]], [[urbanization]], and [[agriculture]].<ref>{{Cite book|authors=Zheng, Xiaojing & Huang, Ning|title=Mechanics of Wind-Blown Sand Movements|publisher=Springer|year=2009|isbn=978-3-540-88253-4|pages=7–8|url=http://books.google.com/books?id=R6kYrbA3XSAC&pg=PA7}}</ref><ref>{{cite book|author=Cornelis, Wim S.|chapter=Hydroclimatology of wind erosion in arid and semi-arid environments|editors=D'Odorico, Paolo & Porporato, Amilcare|title=Dryland Ecohydrology|publisher=Springer|year=2006|isbn=978-1-4020-4261-4|page=141|url=http://books.google.com/books?id=rUsUPZbFHK8C&pg=PA141}}</ref>
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| Wind erosion is of two primary varieties: ''[[Aeolian processes#Wind erosion|deflation]]'', where the wind picks up and carries away loose particles; and ''[[Abrasion (geology)|abrasion]]'', where surfaces are worn down as they are struck by airborne particles carried by wind. Deflation is divided into three categories: (1) ''[[Downhill creep|surface creep]]'', where larger, heavier particles slide or roll along the ground; (2) ''[[Saltation (geology)|saltation]]'', where particles are lifted a short height into the air, and bounce and saltate across the surface of the soil; and (3) ''[[Suspension (chemistry)|suspension]]'', where very small and light particles are lifted into the air by the wind, and are often carried for long distances. Saltation is responsible for the majority (50-70%) of wind erosion, followed by suspension (30-40%), and then surface creep (5-25%).<ref>{{cite book|authors=Blanco, Humberto & Lal, Rattan|chapter=Wind erosion|title=Principles of Soil Conservation and Management|publisher=Springer|year=2010|isbn=978-90-481-8529-0|pages=56–57|url=http://books.google.com/books?id=Wj3690PbDY0C&pg=PA57}}</ref><ref>{{Cite book|author=Balba, A. Monem|chapter=Desertification: Wind erosion|title=Management of Problem Soils in Arid Ecosystems|publisher=CRC Press|year=1995|isbn=978-0-87371-811-0|page=214|url=http://books.google.com/books?id=uS62XNzDZDsC&pg=PA214}}</ref>
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| Wind erosion is much more severe in arid areas and during times of drought. For example, in the [[Great Plains]], it is estimated that soil loss due to wind erosion can be as much as 6100 times greater in drought years than in wet years.<ref>{{Cite book|author=Wiggs, Giles F.S.|chapter=Geomorphological hazards in drylands|editor=Thomas, David S.G.|title=Arid Zone Geomorphology: Process, Form and Change in Drylands|publisher=John Wiley & Sons|year=2011|isbn=978-0-470-71076-0|page=588|url=http://books.google.com/books?id=swz4rh4KaLYC&pg=PA588}}</ref>
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| ===Gravitational erosion===
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| [[File:NegevWadi2009.JPG|thumb|Wadi in Makhtesh Ramon, Israel, showing gravity collapse erosion on its banks.]]
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| ''[[Mass wasting|Mass movement]]'' is the downward and outward movement of rock and sediments on a sloped surface, mainly due to the force of [[gravity]].<ref>{{cite book|authors=Van Beek, Rens|chapter=Hillside processes: mass wasting, slope stability, and erosion|editors=Norris, Joanne E. et al|title=Slope Stability and Erosion Control: Ecotechnological Solutions|publisher=Springer|year=2008|isbn=978-1-4020-6675-7|url=http://books.google.com/books?id=YWPcffxM_A0C&pg=PA17}}</ref><ref>{{cite book|authors=Gray, Donald H. & Sotir, Robbin B.|chapter=Surficial erosion and mass movement|title=Biotechnical and Soil Bioengineering Slope Stabilization: A Practical Guide for Erosion Control|publisher=John Wiley & Sons|year=1996|isbn=978-0-471-04978-4|page=20|url=http://books.google.com/books?id=kCbp6IvFHrAC&pg=20}}</ref>
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| Mass movement is an important part of the erosional process, and is often the first stage in the breakdown and transport of weathered materials in mountainous areas.<ref>{{cite book|author=Nichols, Gary|title=Sedimentology and Stratigraphy|publisher=John Wiley & Sons|year=2009|isbn=978-1-4051-9379-5|page=93|url=http://books.google.com/books?id=zl4L7WqXvogC&pg=PA93}}</ref> It moves material from higher elevations to lower elevations where other eroding agents such as streams and [[glacier]]s can then pick up the material and move it to even lower elevations. Mass-movement processes are always occurring continuously on all slopes; some mass-movement processes act 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]]. 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 form of such activity is a [[scree]] slope.{{Citation needed|date=April 2012}}
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| ''[[Slump (geology)|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 [[isostatic depression]], in 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 [[highway]]s where it is a regular occurrence.{{Citation needed|date=April 2012}}
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| ''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 {{convert|0.5|to|1.0|mm|abbr=on|2}} in diameter by wind along the soil surface.{{Citation needed|date=April 2012}}
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| ===Exfoliation===
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| ''Exfoliation'' is a type of erosion that occurs when a rock is rapidly heated up by the sun. This results in the expansion of the rock. When the temperature decreases again, the rock contracts, causing pieces of the rock to break off. Exfoliation occurs mainly in deserts due to the high temperatures during the day and cold temperatures at night.<ref>See: {{cite book|author=Glennie, K.W.|chapter=Desert erosion and deflation|title=Desert Sedimentary Environments, Volume 14|publisher=Elsevier|year=1970|isbn=978-0-444-40850-1|url=http://books.google.com/books?id=VvAdX7hhfCYC&pg=PA15}}</ref>
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| ===Lightning strikes===
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| When water in cracked rock is rapidly heated by a lightning strike, the resulting steam explosion can erode rock and shift boulders. It may be a significant factor in erosion of tropical and subtropical mountains that have never been glaciated. Evidence of lightning strikes include craters, partially melted rock and erratic magnetic fields.<ref>{{citeweb |url=http://news.nationalgeographic.com/news/2014/01/140105-lightning-mountains-south-africa-drakensberg-mountains-geology/ |title=Shocking News: Lightning Can Shape a Mountain! |publisher=National Geographic Society |date=January 5, 2014}}</ref>
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| ==Factors affecting erosion rates==
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| ===Precipitation and wind speed===
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| Climatic factors include the amount and intensity of [[rainfall|precipitation]], the average temperature, as well as the typical temperature range, seasonality, wind speed, and storm frequency. In general, given similar vegetation and ecosystems, areas with high-intensity precipitation, more frequent rainfall, more wind, or more storms are expected to have more erosion.
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| Rainfall intensity is the primary determinant of erosivity, with higher intensity rainfall generally resulting in more erosion. The size and velocity of rain drops is also an important factor. Larger and higher-velocity rain drops have greater [[kinetic energy]], and thus their impact will displace soil particles by larger distances than smaller, slower-moving rain drops.<ref>{{cite book|authors=Blanco, Humberto & Lal, Rattan|chapter=Water erosion|title=Principles of Soil Conservation and Management|publisher=Springer|year=2010|isbn=978-90-481-8529-0|pages=29–31|url=http://books.google.com/books?id=Wj3690PbDY0C&pg=PA29}}</ref>
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| ===Soil structure and composition===
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| [[Image:Dead Sea Coastal Erosion March 2012.JPG|thumb|Erosional gully in unconsolidated [[Dead Sea]] (Israel) sediments along the southwestern shore. This gully was excavated by floods from the [[Judean Mountains]] in less than a year.]]
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| The composition, moisture, and compaction of soil are all major factors in determining the erosivity of rainfall. Sediments containing more [[clay]] tend to be more resistant to erosion than those with sand or silt, because the clay helps bind soil particles together.<ref>{{cite book|author=Mirsal, Ibrahim A.|chapter=Soil degradation|title=Soil Pollution: Origin, Monitoring & Remediation|publisher=Springer|year=2008|isbn=978-3-540-70775-2|page=100|url=http://books.google.com/books?id=Lr5bMTxom0IC&pg=PA100}}</ref> Soil containing high levels of organic materials are often more resistant to erosion, because the organic materials coagulate soil colloids and create a stronger, more stable soil structure.<ref name="Blanco-2010-p29" /> The amount of water present in the soil before the precipitation also plays an important role, because it sets limits on the amount of water that can be absorbed by the soil (and hence prevented from flowing on the surface as erosive runoff). Wet, saturated soils will not be able to absorb as much rain water, leading to higher levels of surface runoff and thus higher erosivity for a given volume of rainfall.<ref name="Blanco-2010-p29" /><ref>{{cite book|author=Torri, D.|chapter=Slope, aspect and surface storage|editor=Agassi, Menachem|title=Soil Erosion, Conservation, and Rehabilitation|publisher=CRC Press|year=1996|isbn=978-0-8247-8984-8|page=95|url=http://books.google.com/books?id=-AqdSMDSUIgC&pg=PA95}}</ref> Soil compaction also affects the permeability of the soil to water, and hence the amount of water that flows away as runoff. More compacted soils will have a larger amount of surface runoff than less compacted soils.<ref name="Blanco-2010-p29">{{cite book|authors=Blanco, Humberto & Lal, Rattan|chapter=Water erosion|title=Principles of Soil Conservation and Management|publisher=Springer|year=2010|isbn=978-90-481-8529-0|page=29|url=http://books.google.com/books?id=Wj3690PbDY0C&pg=PA29}}</ref>
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| ===Vegetative cover===
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| {{See also|Vegetation and slope stability}}
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| Vegetation acts as an interface between the atmosphere and the soil. It increases the [[permeability (earth sciences)|permeability]] of the soil to rainwater, thus decreasing runoff. It shelters the soil from winds, which results in decreased wind erosion, as well as advantageous changes in microclimate. The roots of the plants bind the soil together, and interweave with other roots, forming a more solid mass that is less susceptible to both water and wind erosion. The removal of vegetation increases the rate of surface erosion.<ref>{{cite book|authors=Styczen, M.E. & Morgan, R.P.C.|chapter=Engineering properties of vegetation|editors=Morgan, R.P.C. & Rickson, R. Jane|title=Slope Stabilization and Erosion Control: A Bioengineering Approach|publisher=Taylor & Francis|year=1995|isbn=978-0-419-15630-7|url=http://books.google.com/books?id=3jXg9pyfikQC&pg=4}}</ref>
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| ===Topography===
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| The topography of the land determines the velocity at which [[surface runoff]] will flow, which in turn determines the erosivity of the runoff. Longer, steeper slopes (especially those without adequate vegetative cover) are more susceptible to very high rates of erosion during heavy rains than shorter, less steep slopes. Steeper terrain is also more prone to mudslides, landslides, and other forms of gravitational erosion processes.<ref>{{cite book|author=Whisenant, Steve G.|chapter=Terrestrial systems|editors=Perrow Michael R. & Davy, Anthony J.|title=Handbook of Ecological Restoration: Principles of Restoration|publisher=Cambridge University Press|year=2008|isbn=978-0-521-04983-2|page=89|url=http://books.google.com/books?id=moJHjZ9qW_8C&pg=PA89}}</ref><ref>{{cite book|authors=Blanco, Humberto & Lal, Rattan|chapter=Water erosion|title=Principles of Soil Conservation and Management|publisher=Springer|year=2010|isbn=978-90-481-8529-0|pages=28–30|url=http://books.google.com/books?id=Wj3690PbDY0C&pg=PA28}}</ref><ref>{{cite book|authors=Wainwright, John & Brazier, Richard E.|chapter=Slope systems|editor=Thomas, David S.G.|title=Arid Zone Geomorphology: Process, Form and Change in Drylands|publisher=John Wiley & Sons|year=2011|isbn=978-0-470-71076-0|url=http://books.google.com/books?id=swz4rh4KaLYC&pg=PA209}}</ref>
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| ==Human activities that increase erosion rates==
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| ===Agricultural practices===
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| [[File:Soil erosion at Hill Farm - geograph.org.uk - 1287527.jpg|thumb|Tilled farmland such as this is very susceptible to erosion from rainfall, due to the destruction of vegetative cover and the loosening of the soil during plowing.]]
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| Unsustainable agricultural practices are the single greatest contributor to the global increase in erosion rates.<ref>{{Cite book|authors=Committee on 21st Century Systems Agriculture|title=Toward Sustainable Agricultural Systems in the 21st Century|publisher=National Academies Press|year=2010|isbn=978-0-309-14896-2|url=http://books.google.com/books?id=wdm4qMW1azgC&pg=PT88}}</ref>
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| The [[tillage]] of agricultural lands, which breaks up soil into finer particles, is one of the primary factors. The problem has been exacerbated in modern times, due to mechanized agricultural equipment that allows for [[deep plowing]], which severely increases the amount of soil that is available for transport by water erosion. Others include [[mono-cropping]], farming on steep slopes, [[pesticide]] and [[chemical fertilizer]] usage (which kill organisms that bind soil together), row-cropping, and the use of [[surface irrigation]].<ref>{{cite book|authors=Blanco, Humberto & Lal, Rattan|chapter=Tillage erosion|title=Principles of Soil Conservation and Management|publisher=Springer|year=2010|isbn=978-90-481-8529-0|url=http://books.google.com/books?id=Wj3690PbDY0C&pg=PA109}}</ref><ref>{{cite book|author=Lobb, D.A.|chapter=Soil movement by tillage and other agricultural activities|editor=Jorgenson, Sven E.|title=Applications in Ecological Engineering|publisher=Academic Press|year=2009|isbn=978-0-444-53448-4|url=http://books.google.com/books?id=aRKO6ZazC8UC&pg=PA247}}</ref> A complex overall situation with respect to defining nutrient losses from soils, could arise as a result of the size selective nature of soil erosion events. Loss of total [[phosphorus]], for instance, in the finer eroded fraction is greater relative to the whole soil.<ref>{{cite journal |title=Bioavailable phosphorus in fine-sized sediments transported from agricultural fields |author= Poirier, S.-C. Whalen, J.K., Michaud, A.R. |year= 2012|volume=76|issue=1|pages=258–267|doi= 10.2136/sssaj2010.0441
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| |journal= Soil Science Society of America Journal }}</ref> Extrapolating this evidence to predict subsequent behaviour within receiving aquatic systems, the reason is that this more easily transported material may support a lower solution P concentration compared to coarser sized fractions.<ref>{{cite journal |title= Phosphorus loss in overfertilized soils: The selective P partitioning and redistribution between particle size separates |author= Scalenghe, R., Edwards, A.C., and Barberis, E.|year= 2007|volume=27|issue=11|pages=72–80|doi= 10.1016/j.eja.2007.02.002|journal= European Journal of Agronomy}}</ref> Tillage also increases wind erosion rates, by dehydrating the soil and breaking it up into smaller particles that can be picked up by the wind. Exacerbating this is the fact that most of the trees are generally removed from agricultural fields, allowing winds to have long, open runs to travel over at higher speeds.<ref>{{cite book|author=Whitford, Walter G.|chapter=Wind and water processes|title=Ecology of Desert Systems|publisher=Academic Press|year=2002|isbn=978-0-12-747261-4|page=65|url=http://books.google.com/books?id=OZ4hZbXS8IcC&pg=PA65}}</ref> Heavy [[grazing]] reduces vegetative cover and causes severe soil compaction, both of which increase erosion rates.<ref>{{cite book|author=Imeson, Anton|chapter=Human impact on degradation processes|title=Desertification, Land Degradation and Sustainability|publisher=John Wiley & Sons|year=2012|isbn=978-1-119-97776-6|page=165|url=http://books.google.com/books?id=BjJQY-i7kNsC&pg=PA165}}</ref>
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| ===Deforestation===
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| [[File:BURNED CLEAR-CUT AREA OF OLYMPIC NATIONAL TIMBERLAND WASHINGTON. NEAR OLYMPIC NATIONAL PARK - NARA - 555088.tif|thumb|In this [[clearcut]], almost all of the vegetation has been stripped from surface of steep slopes, in an area with very heavy rains. Severe erosion occurs in cases such as this, causing stream [[sedimentation]] and the loss of nutrient rich [[topsoil]].]]
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| In an undisturbed [[forest]], the mineral soil is protected by a layer of ''[[leaf litter]]'' and an ''[[humus]]'' that cover the forest floor. These two layers form a protective mat over the soil that absorbs the impact of rain drops. They are [[porosity|porous]] and highly [[permeability (earth sciences)|permeable]] to rainfall, and allow rainwater to slow [[percolate]] into the soil below, instead of flowing over the surface as [[surface runoff|runoff]].<ref name="Sands-2005-pp74-75">{{cite book|author=Sands, Roger|chapter=The environmental value of forests|title=Forestry in a Global Context|publisher=CABI|year=2005|isbn=978-0-85199-089-7|pages=74–75|url=http://books.google.com/books?id=UO1DAI60IQEC&pg=PA74}}</ref> The roots of the trees and plants<ref>The [[mycelia]] of forest [[fungi]] also play a major role in binding soil particles together.</ref> hold together soil particles, preventing them from being washed away.<ref name="Sands-2005-pp74-75" /> The vegetative cover acts to reduce the velocity of the raindrops that strike the foliage and stems before hitting the ground, reducing their [[kinetic energy]].<ref name="Goudie-2000-p188" /> However it is the forest floor, more than the canopy, that prevents surface erosion. The [[terminal velocity]] of rain drops is reached in about {{convert|8|m|ft|abbr=off}}. Because forest canopies are usually higher than this, rain drops can often regain terminal velocity even after striking the canopy. However, the intact forest floor, with its layers of leaf litter and organic matter, is still able to absorb the impact of the rainfall.<ref name="Goudie-2000-p188">{{Cite book|author=Goudie, Andrew|chapter=The human impact on the soil|title=The Human Impact on the Natural Environment|publisher=MIT Press|year=2000|isbn=978-0-262-57138-8|page=188|url=http://books.google.com/books?id=r8l-DMj3XTgC&pg=PA188}}</ref><ref>{{cite journal|authors=Stuart, Gordon W. & Edwards, Pamela J.|title=Concepts about forests and water|work=Northern Journal of Applied Forestry|volume=23|issue=1|year=2006|url=http://treesearch.fs.fed.us/pubs/14744}}</ref>
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| [[Deforestation]] causes increased erosion rates due to exposure of [[mineral]] [[soil]] by removing the humus and litter layers from the soil surface, removing the vegetative cover that binds soil together, and causing heavy [[soil compaction]] from logging equipment. Once trees have been removed by fire or logging, infiltration rates become high and erosion low to the degree the forest floor remains intact. Severe fires can lead to significant further erosion if followed by heavy rainfall.<ref>{{Cite book|author=Goudie, Andrew|chapter=The human impact on the soil|title=The Human Impact on the Natural Environment|publisher=MIT Press|year=2000|isbn=978-0-262-57138-8|pages=196–197|url=http://books.google.com/books?id=r8l-DMj3XTgC&pg=PA196}}</ref>
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| Globally one of the largest contributors to erosive soil loss in the year 2006 is the [[slash and burn]] treatment of [[tropical]] [[forest]]s. 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 {{convert|50|m|ft}} deep and {{convert|1|km|mi|abbr=off|1}} wide. [[Shifting cultivation]] is a farming system which sometimes incorporates the [[slash and burn]] method in some regions of the world. This degrades the soil and causes the soil to become less and less fertile.{{citation needed|date=October 2011}}
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| ===Roads and urbanization===
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| [[Urbanization]] has major effects on erosion processes—first by denuding the land of vegetative cover, altering drainage patterns, and compacting the soil during construction; and next by covering the land in an impermeable layer of asphalt or concrete that increases the amount of surface runoff and increases surface wind speeds.<ref>{{cite book|author=Nîr, Dov|title=Man, a Geomorphological Agent: An Introduction to Anthropic Geomorphology|publisher=Springer|year=1983|isbn=978-90-277-1401-5|pages=121–122|url=http://books.google.com/books?id=3HSCQvZ7U2kC&pg=PA121}}</ref> Much of the sediment carried in runoff from urban areas (especially roads) is highly contaminated with fuel, oil, and other chemicals.<ref>{{cite book|author=Randhir, Timothy O.|title=Watershed Management: Issues and Approaches|publisher=IWA Publishing|year=2007|isbn=978-1-84339-109-8|page=56|url=http://books.google.com/books?id=PNBlSPdu0JAC&pg=PA56}}</ref> This increased runoff, in addition to eroding and degrading the land that it flows over, also causes major disruption to surrounding watersheds by altering the volume and rate of water that flows through them, and filling them with chemically polluted sedimentation. The increased flow of water through local waterways also causes a large increase in the rate of bank erosion.<ref>{{cite book|author=James, William|chapter=Channel and habitat change downstream of urbanization|editors=Herricks, Edwin E. & Jenkins, Jackie R.|title=Stormwater Runoff and Receiving Systems: Impact, Monitoring, and Assessment|publisher=CRC Press|year=1995|isbn=978-1-56670-159-4|page=105|url=http://books.google.com/books?id=X0xt9HZbyToC&pg=PA105}}</ref>
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| ===Climate change===
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| {{Main|Land degradation}}
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| The warmer atmospheric temperatures observed over the past decades are expected to lead to a more vigorous hydrological cycle, including more extreme rainfall events.<ref>{{cite web|author=Intergovernmental Panel on Climate Change (IPCC)|year=1995|title=Second Assessment Synthesis of Scientific-Technical Information relevant to interpreting Article 2 of the UN Framework Convention on Climate Change|page=5|url=http://www.ipcc.ch/pdf/climate-changes-1995/2nd-assessment-synthesis.pdf}}</ref> The [[rise in sea levels]] that has occurred as a result of climate change has also greatly increased coastal erosion rates.<ref>{{cite book|editors=Bicknell, Jane et al|title=Adapting Cities to Climate Change: Understanding and Addressing the Development Challenges|publisher=Earthscan|year=2009|isbn=978-1-84407-745-8|page=114|url=http://books.google.com/books?id=77Kmhw6sVOMC&pg=PA114}}</ref><ref>For an overview of other human activities that have increased coastal erosion rates, see: {{cite book|author=Goudie, Andrew|chapter=Accelerated coastal erosion|title=The Human Impact on the Natural Environment|publisher=MIT Press|year=2000|isbn=978-0-262-57138-8|page=311|url=http://books.google.com/books?id=r8l-DMj3XTgC&pg=PA311}}</ref>
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| Studies on soil erosion suggest that increased rainfall amounts and intensities will lead to greater rates of erosion. Thus, if rainfall amounts and intensities increase in many parts of the world as expected, erosion will also increase, unless amelioration measures are taken. Soil erosion rates are expected to change in response to changes in climate for a variety of reasons. The most direct is the change in the erosive power of rainfall. Other reasons include: a) changes in plant canopy caused by shifts in plant biomass production associated with moisture regime; b) changes in litter cover on the ground caused by changes in both plant residue decomposition rates driven by temperature and moisture dependent soil microbial activity as well as plant biomass production rates; c) changes in soil moisture due to shifting precipitation regimes and evapo-transpiration rates, which changes infiltration and runoff ratios; d) soil erodibility changes due to decrease in soil organic matter concentrations in soils that lead to a soil structure that is more susceptible to erosion and increased runoff due to increased soil surface sealing and crusting; e) a shift of winter precipitation from non-erosive snow to erosive rainfall due to increasing winter temperatures; f) melting of permafrost, which induces an erodible soil state from a previously non-erodible one; and g) shifts in land use made necessary to accommodate new climatic regimes.{{Citation needed|date=April 2012}}
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| Studies by Pruski and Nearing indicated that, other factors such as land use not considered, it is reasonable to expect approximately a 1.7% change in soil erosion for each 1% change in total precipitation under climate change.<ref>{{cite journal |last=Pruski |first=F. F. |first2=M. A. |last2=Nearing |year=2002 |title=Runoff and soil loss responses to changes in precipitation: a computer simulation study |journal=Journal of Soil and Water Conservation |volume=57 |issue=1 |pages=7–16 |url=http://www.jswconline.org/content/57/1/7.abstract }}</ref>
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| ==Global environmental effects==
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| [[File:Water erosion map.jpg|thumb|325px|World map indicating areas that are vulnerable to high rates of water erosion.]]
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| [[File:Rano Raraku quarry.jpg|thumb|During the 17th and 18th centuries, [[Easter Island]] experienced severe erosion due to [[deforestation]] and unsustainable agricultural practices. The resulting loss of topsoil ultimately led to ecological collapse, causing mass [[starvation]] and the complete disintegration of the Easter Island civilization.<ref>{{cite journal|author=Dangerfield, Whitney|title=The Mystery of Easter Island|work=Smithsonian Magazine|date=April 1, 2007|url=http://www.smithsonianmag.com/people-places/The_Mystery_of_Easter_Island.html}}</ref><ref>{{cite book|author=Montgomery, David|chapter=Islands in time|title=Dirt: The Erosion of Civilizations|publisher=University of California Press|date=October 2, 2008|edition=1st|isbn=978-0-520-25806-8|url=http://books.google.com/books?id=HSu8r15-nnoC&pg=PA217}}</ref>]]
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| Due to the severity of its ecological effects, and the scale on which it is occurring, erosion constitutes one of the most significant global environmental problems we face today.<ref name="toy-2002-p1">{{cite book|authors=Toy, Terrence J. et al|title=Soil Erosion: Processes, Predicition, Measurement, and Control|publisher=John Wiley & Sons|year=2002|isbn=978-0-471-38369-7|page=1|url=http://books.google.com/books?id=7YBaKZ-28j0C&pg=PA1}}</ref>
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| ===Land degradation===
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| Water and wind erosion are now the two primary causes of [[land degradation]]; combined, they are responsible for 84% of degraded acreage.<ref name="Springer"/>
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| Each year, about 75 billion tons of soil is eroded from the land—a rate that is about 13-40 times as fast as the natural rate of erosion.<ref>{{cite book|authors=Zuazo, Victor H.D. & Pleguezuelo, Carmen R.R.|chapter=Soil-erosion and runoff prevention by plant covers: a review|editors=Lichtfouse, Eric et al.|title=Sustainable agriculture|publisher=Springer|year=2009|isbn=978-90-481-2665-1|page=785|url=http://books.google.com/books?id=7cP-2jIIO2wC&pg=PA785}}</ref> Approximately 40% of the world's agricultural land is seriously degraded.<ref>{{cite news|author=Sample, Ian|title=Global food crisis looms as climate change and population growth strip fertile land|work=The Guardian|date=August 30, 2007|url=http://www.guardian.co.uk/environment/2007/aug/31/climatechange.food}}</ref> According to the [[United Nations]], an area of fertile soil the size of Ukraine is lost every year because of [[drought]], [[deforestation]] and [[climate change]].<ref>{{cite news|authors=Smith, Kate & Edwards, Rob|title=2008: The year of global food crisis|work=The Herald (Scotland)|date=March 8, 2008|url=http://www.heraldscotland.com/2008-the-year-of-global-food-crisis-1.828546}}</ref> In [[Africa]], if current trends of soil degradation continue, the continent might be able to feed just 25% of its population by 2025, according to [[United Nations University|UNU]]'s Ghana-based Institute for Natural Resources in Africa.<ref>[http://news.mongabay.com/2006/1214-unu.html Africa may be able to feed only 25% of its population by 2025]</ref>
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| The loss of soil fertility due to erosion is further problematic because the response is often to apply chemical fertilizers, which leads to further water and soil pollution, rather than to allow the land to regenerate.<ref>{{cite book|authors=Potter, Kenneth W. et al|chapter=Impacts of agriculture on aquatic ecosystems in the humid United States|editors=DeFries, Ruth S. et al|title=Ecosystems And Land Use Change|publisher=American Geophysical Union|year=2004|isbn=978-0-87590-418-4|page=34|url=http://books.google.com/books?id=CVN5X57pjnAC&pg=PA34}}</ref>
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| ===Sedimentation of aquatic ecosystems===
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| Soil erosion (especially from agricultural activity) is considered to be the leading global cause of diffuse [[water pollution]], due to the effects of the excess sediments flowing into the world's waterways. The sediments themselves act as pollutants, as well as being carriers for other pollutants, such as attached pesticide molecules or heavy metals.<ref>{{Cite book|author=Da Cunha, L.V.|chapter=Sustainable development of water resources|editor=Bau, João|title=Integrated Approaches to Water Pollution Problems: Proceedings of the International Symposium (SISIPPA) (Lisbon, Portugal 19–23 June 1989)|publisher=Taylor & Francis|year=1991|isbn=978-1-85166-659-1|pages=12–13|url=http://books.google.com/books?id=79ztZNhaNvMC&pg=PA12}}</ref>
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| The effect of increased sediments loads on aquatic ecosystems can be catastrophic. Silt can smother the spawning beds of fish, by filling in the space between gravel on the stream bed. It also reduces their food supply, and causes major respiratory issues for them as sediment enters their [[gills]]. The [[biodiversity]] of aquatic plant and algal life is reduced, and invertebrates are also unable to survive and reproduce. While the sedimentation event itself might be relatively short-lived, the ecological disruption caused by the mass die off often persists long into the future.<ref>{{Cite book|author=Merrington, Graham|chapter=Soil erosion|title=Agricultural Pollution: Environmental Problems and Practical Solutions|publisher=Taylor & Francis|year=2002|isbn=978-0-419-21390-1|pages=77–78|url=http://books.google.com/books?id=ITFYBiQ_-VAC&pg=PA77}}</ref>
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| One of the most serious and long-running water erosion problems worldwide is in the [[People's Republic of China]], on 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 flows into the ocean each year. The [[sediment]] originates primarily from water erosion in the [[Loess Plateau]] region of the northwest.{{citation needed|date=October 2011}}
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| ===Airborne dust pollution===
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| Soil particles picked up during wind erosion are a major source of [[air pollution]], in the form of [[airborne particulates]]—"dust". These airborne soil particles are often contaminated with toxic chemicals such as pesticides or petroleum fuels, posing ecological and public health hazards when they later land, or are inhaled/ingested.<ref>{{cite book|authors=Majewski, Michael S. & Capel, Paul D.|title=Pesticides in the Atmosphere: Distribution, Trends, and Governing Factors|publisher=CRC Press|year=1996|isbn=978-1-57504-004-2|page=121|url=http://books.google.com/books?id=T9pRfLqXajQC&pg=PA121}}</ref><ref name=autogenerated2>{{cite web|author=Science Daily|date=1999-07-14|url=http://www.sciencedaily.com/releases/1999/07/990714073433.htm|title=African Dust Called A Major Factor Affecting Southeast U.S. Air Quality|accessdate=2007-06-10}}</ref><ref>{{cite book|authors=Nowell, Lisa H. et al|title=Pesticides in Stream Sediment and Aquatic Biota: Distribution, Trends, and Governing Factors|publisher=CRC Press|year=1999|isbn=978-1-56670-469-4|page=199|url=http://books.google.com/books?id=UzpDTEO3ZVcC&pg=PA199}}</ref><ref>{{cite book|authors=Shao, Yaping|chapter=Wind-erosion and wind-erosion research|title=Physics and Modelling of Wind Erosion|publisher=Springer|year=2008|isbn=978-1-4020-8894-0|page=3|url=http://books.google.com/books?id=XSwwVeraxjcC&pg=PA3}}</ref>
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| Dust from erosion acts to suppress rainfall and changes the [[sky]] color from blue to white, which leads to an increase in red sunsets. Over 50% of the African dust that reaches the United States affects Florida.<ref>{{cite web|author=Science Daily|date=2001-06-15|url=http://www.sciencedaily.com/releases/2001/06/010615071508.htm|title=Microbes And The Dust They Ride In On Pose Potential Health Risks|accessdate=2007-06-10}}</ref> Dust events have been linked to a decline in the health of [[coral reef]]s across the Caribbean and Florida, primarily since the 1970s.<ref>{{cite web|author=[[U. S. Geological Survey]]|year=2006|url=http://coastal.er.usgs.gov/african_dust/|title=Coral Mortality and African Dust|accessdate=2007-06-10}}</ref> Similar dust plumes originate in the [[Gobi desert]], which combined with pollutants, spread large distances downwind, or eastward, into North America.<ref name="Gobi">{{cite web|author=James K. B. Bishop, Russ E. Davis, and Jeffrey T. Sherman|year=2002|url=http://www-ocean.lbl.gov/people/bishop/bishoppubs/paparobots.html|title=Robotic Observations of Dust Storm Enhancement of Carbon Biomass in the North Pacific|work=Science 298|pages=817–821|accessdate=2009-06-20|archiveurl = http://www.webcitation.org/5uLajGMw8 |archivedate = 2010-11-18|deadurl=no}}</ref>
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| ===Tectonic effects===
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| {{Expand section|date=April 2012}}
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| {{Main|Erosion and tectonics}}
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| 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 [[crust (geology)|lower crust]] and [[mantle (geology)|mantle]]. This can cause [[tectonic uplift|tectonic]] or [[isostasy|isostatic uplift]] in the region.<ref>{{cite book|author=Nichols, Gary|title=Sedimentology and Stratigraphy|publisher=John Wiley & Sons|edition=2nd|year=2009|isbn=978-1-4051-9379-5|page=99|url=http://books.google.com/books?id=zl4L7WqXvogC&pg=PA99}}</ref><ref>{{cite book|author=Burbank, Douglas W. & Anderson, Robert S.|chapter=Tectonic and surface uplift rates|title=Tectonic Geomorphology|publisher=John Wiley & Sons|year=2011|isbn=978-1-4443-4504-9|pages=270–271|url=http://books.google.com/books?id=83FuAvtSwE4C&pg=PT270}}</ref>
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| ==Monitoring, measuring, and modeling erosion==
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| [[File:Landscape Madagascar 06.jpg|thumb|[[Terrace (agriculture)|Terracing]] is an ancient technique that can significantly slow the rate of water erosion on cultivated slopes.]]
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| {{See also|Erosion prediction}}
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| {{Expand section|date=April 2012}}
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| Monitoring and modeling of erosion processes can help us better understand the causes, make predictions, and plan how to implement preventative and restorative strategies. However, the complexity of erosion processes and the number of areas that must be studied to understand and model them (e.g. climatology, hydrology, geology, chemistry, physics, etc.) makes accurate modelling quite challenging.<ref>{{cite book|authors=Blanco, Humberto & Lal, Rattan|chapter=Modeling water and wind erosion|title=Principles of Soil Conservation and Management|publisher=Springer|year=2010|isbn=978-90-481-8529-0|url=http://books.google.com/books?id=Wj3690PbDY0C&pg=PA81}}</ref><ref>See also: {{cite book|author=Shai, Yaping|title=Physics and Modelling of Wind Erosion|publisher=Springer|year=2008|isbn=978-1-4020-8894-0|url=http://books.google.com/books?id=XSwwVeraxjcC}} and {{cite book|author=Harmon, Russell S. & Doe, William W.|title=Landscape Erosion and Evolution Modeling|publisher=Springer|year=2001|isbn=978-0-306-46718-9|url=http://books.google.com/books?id=RltaPlIHlrAC}}</ref> Erosion models are also non-linear, which makes them difficult to work with numerically, and makes it difficult or impossible to scale up to making predictions about large areas from data collected by sampling smaller plots.<ref>{{cite book|authors=Brazier, R.E. et al|chapter=Scaling soil erosion models in space and time|editors=Morgan, Royston P.C. & Nearing, Mark|title=Handbook of Erosion Modelling|publisher=John Wiley & Sons|year=2011|isbn=978-1-4051-9010-7|page=100|url=http://books.google.com/books?id=pSO4X3XbhJIC&pg=PA100}}</ref>
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| The most commonly used model for predicting soil loss from water erosion is the ''[[Universal Soil Loss Equation|Universal Soil Loss Equation (USLE)]]'', which estimates the average annual soil loss <math>A</math> as:<ref>{{cite book|authors=Ward, Andrew D. & Trimble, Stanley W.|chapter=Soil conservation and sediment budgets|title=Environmental Hydrology|publisher=CRC Press|year=2004|isbn=978-1-56670-616-2|page=259|url=http://books.google.com/books?id=yANwmTjf588C&pg=PA259}}</ref>
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| :<math>A = RKLSCP</math>
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| where ''R'' is the rainfall erosivity factor, ''K'' is the soil erodibility factor, ''L'' and ''S'' are [[topographic]] factors representing length and slope, and ''C'' and ''P'' are cropping management factors.
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| A new soil erosion model named G2 monitors soil erosion by a spatio-temporal index. [http://eusoils.jrc.ec.europa.eu/library/themes/erosion/G2/data.html G2] is a dynamic model, as it takes account of contemporary changes of rainfall erosivity and vegetation retention. Based on the empirical USLE-family models, it needs calibration for rainstorm erosivity, while vegetation retention is based on biophysical parameters derived with remote sensing.
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| Erosion is measured and further understood using tools such as the [[micro-erosion meter]] (MEM) and the [[traversing micro-erosion meter]] (TMEM). The MEM has proved helpful in measuring bedrock erosion in various ecosystems around the world. It can measure both terrestrial and oceanic erosion. On the other hand, the TMEM can be used to track the expanding and contracting of volatile rock formations and can give a reading of how quickly a rock formation is deteriorating.{{Citation needed|date=April 2012}}
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| ==Prevention and remediation==
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| {{See also|Erosion control|Erosion control#Examples|l2=Erosion control examples}}
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| [[File:Windbreak near New Alyth - geograph.org.uk - 687555.jpg|thumb|A [[windbreak]] (the row of trees) planted next to an agricultural field, acting as a shield against strong winds. This reduces the effects of wind erosion, and provides many other benefits.]]
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| The most effective known method for erosion prevention is to increase vegetative cover on the land, which helps prevent both wind and water erosion.<ref>{{cite book|authors=Connor, David J. et al|title=Crop Ecology: Productivity and Management in Agricultural Systems|publisher=Cambridge University Press|year=2011|isbn=978-0-521-74403-4|page=351|url=http://books.google.com/books?id=O2eh7vyvuscC&pg=PA351}}</ref> [[Terrace (agriculture)|Terracing]] is an extremely effective means of erosion control, which has been practiced for thousands of years by people all over the world.<ref>For an interesting archaeological/historical survey of terracing systems, see {{cite book|authors=Treacy, John M. & Denevan, William M.|chapter=The creation of cultivable land through terracing|editor=Miller, Naomi A.|title=The Archaeology of Garden and Field|publisher=University of Pennsylvania Press|year=1998|isbn=978-0-8122-1641-7|url=http://books.google.com/books?id=MARsWXbqFCsC&pg=PA91}}</ref> [[Windbreaks]] (also called shelterbelts) are rows of trees and shrubs that are planted along the edges of agricultural fields, to shield the fields against winds.<ref>{{Cite book|author=Forman, Richard T.T.|chapter=Windbreaks, hedgerows, and woodland corridors|title=Land Mosaics: The Ecology of Landscapes and Regions|publisher=Cambridge University Press|year=1995|isbn=978-0-521-47980-6|url=http://books.google.com/books?id=sSRNU_5P5nwC&pg=PA177}}</ref> In addition to significantly reducing wind erosion, windbreaks provide many other benefits such as improved [[microclimate]]s for crops (which are sheltered from the dehydrating and otherwise damaging effects of wind), habitat for beneficial bird species,<ref>{{cite book|authors=Johnson, R.J. et al|chapter=Global perspectives on birds in agricultural landscapes|editors=Campbell, W. Bruce & Ortiz, Silvia Lopez|title=Integrating Agriculture, Conservation and Ecotourism: Examples from the Field|publisher=Springer|year=2011|isbn=978-94-007-1308-6|page=76|url=http://books.google.com/books?id=85KuKnayVMEC&pg=PA76}}</ref> [[carbon sequestration]],<ref>{{cite book|authors=Udawatta, Ranjith P. & Shibu, Jose|chapter=Carbon sequestration potential of agroforestry practices in temperate North America|editors=Kumar, B. Mohan & Nair, P.K.R.|title=Carbon Sequestration Potential of Agroforestry Systems: Opportunities and Challenges|publisher=Springer|year=2011|isbn=978-94-007-1629-2|pages=35–36|url=http://books.google.com/books?id=oDzvVdD_dHwC&pg=PA35}}</ref> and aesthetic improvements to the agricultural landscape.<ref>{{cite book|authors=Blanco, Humberto & Lal, Rattan|chapter=Wind erosion|title=Principles of Soil Conservation and Management|publisher=Springer|year=2010|isbn=978-90-481-8529-0|page=69|url=http://books.google.com/books?id=Wj3690PbDY0C&pg=PA69}}</ref><ref>{{cite book|author=Nair, P.K.R.|title=An Introduction to Agroforestry|publisher=Springer|year=1993|isbn=978-0-7923-2135-4|pages=333–338|url=http://books.google.com/books?id=CkVSeRpmIx8C&pg=PA333}}</ref> Traditional planting methods, such as mixed-cropping (instead of [[monocropping]]) and [[crop rotation]] have also been shown to significantly reduce erosion rates.<ref>{{cite book|author=Lal, Rattan|title=Tillage Systems in the Tropics: Management Options and Sustainability Implications, Issue 71|publisher=Food and Agriculture Organization of the United Nations|year=1995|isbn=978-92-5-103776-8|pages=157–160|url=http://books.google.com/books?id=Cxxj2VczLG0C&pg=PA157}}</ref><ref>See also: {{cite book|authors=Gajri, P.R. et al|title=Tillage for sustainable cropping|publisher=Psychology Press|year=2002|isbn=978-1-56022-903-2|url=http://books.google.com/books?id=i_acg2gACb8C}} and {{cite book|author=Uri, Noel D.|title=Conservation Tillage in United States Agriculture|publisher=Psychology Press|year=1999|isbn=978-1-56022-884-4|url=http://books.google.com/books?id=2uPYFG3XLoEC}}</ref>
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| ==See also==
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| <div style="-moz-column-count:3; column-count:3;">
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| * [[Badland]]
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| * [[Biorhexistasy]]
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| * [[Bridge scour]]
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| * [[Cellular confinement]]
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| * [[Coastal sediment supply]]
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| * [[Denudation]]
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| * [[Food security]]
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| * [[Geomorphology]]
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| * [[Groundwater sapping]]
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| * [[Highly erodible land]]
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| * [[Ice jacking]]
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| * [[Lessivage]]
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| * [[Marine terrace]]
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| * [[Riparian strips]]
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| * [[River anticlines]]
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| * [[Sediment transport]]
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| * [[Sphericity scale]]
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| * [[TERON (Tillage erosion)]]
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| * [[Vegetation and slope stability]]
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| * [[Vetiver System]]
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| </div>
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| ==Notes==
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| {{reflist|30em}}
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| ==Further reading==
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| {{Refbegin}}
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| * {{cite book|last=Boardman|first=John|coauthors=Poesen, Jean|authorlink=J. Boardman|title=Soil erosion in Europe|publisher=[[John Wiley & Sons|Wiley]]|year=2006|isbn=978-0-470-85910-0}}
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| *{{cite book|author=Montgomery, David|title=Dirt: The Erosion of Civilizations|publisher=University of California Press|date=October 2, 2008|edition=1st|isbn=978-0-520-25806-8|url=http://books.google.com/books?id=HSu8r15-nnoC}}
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| * Montgomery, David R. (2007) [http://www.pnas.org/content/104/33/13268.abstract Soil erosion and agricultural sustainability] PNAS 104: 13268-13272.
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| * {{cite book|last=Brown|first=Jason|coauthors=Drake, Simon|title=Classic Erosion|publisher=[[John Wiley & Sons|Wiley]]|year=2009|isbn=}}
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| * {{cite book|editor=Vanoni, Vito A.|chapter=The nature of sedimentation problems|title=Sedimentation Engineering|publisher=ASCE Publications|year=|isbn=978-0-7844-0823-0|url=http://books.google.com/books?id=TxGTDYz_FnwC&pg=PA1}}
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| * [http://www.csf-desertification.eu/dossier/item/fighting-wind-erosion Mainguet M. & Dumay F., 2011. Fighting wind erosion. One aspect of the combat against desertification. Les dossiers thématiques du CSFD. N°3. May 2011. CSFD/Agropolis International, Montpellier, France. 44 pp.]
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| {{Refend}}
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| ==External links==
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| {{Sister project links|Erosion}}
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| * [http://www.soilerosion.net/ The Soil Erosion Site]
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| * [http://www.ieca.org/ International Erosion Control Association]
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| * [http://eusoils.jrc.ec.europa.eu/library/themes/erosion/ Soil Erosion Data] in the European Soil Portal
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| * [http://www.ars.usda.gov/main/site_main.htm?modecode=36021500 USDA National Soil Erosion Laboratory]
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| * [http://www.swcs.org/ The Soil and Water Conservation Society]
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| * [http://www.isco.org/ International Soil Conservation Organization]
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| * [http://www3.wooster.edu/geology/Bioerosion/Bioerosion.html Bioerosion website at The College of Wooster]
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| * [http://www.erozja.iung.pulawy.pl/ Pulawy Erosion Research Center]
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| * [http://www.tucson.ars.ag.gov/SWRC/MAINSITE/main/site_mainb77c.html Southwest Watershed Research Center]
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| {{River morphology}}
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| [[Category:Erosion| ]]
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| [[Category:Soil science]]
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| [[Category:Agronomy]]
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| [[Category:Industrial agriculture]]
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| [[Category:Environmental soil science]]
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| [[Category:Environmental issues]]
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| [[Category:Desertification]]
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| {{Link GA|tr}}
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