Sheet erosion

[[File:Sheet erosion, Pullman, Washington, 1946 - DPLA - 08b40b5075ee6a427874f36adb2b815f.jpg|thumb|Sheet erosion, Pullman, Washington, 1946]] '''Sheet erosion''' or ''' sheet wash''' is the even erosion of substrate along a wide area.<ref>{{cite web|url=https://www.merriam-webster.com/dictionary/sheet%20erosion|title=Definition of Sheet Erosion|publisher=Merriam-Webster|access-date=23 May 2018}}</ref> It occurs in a wide range of settings such as coastal plains, hill slopes, floodplains, beaches,<ref name=Govers>{{cite encyclopedia|last=Govers|first=Gerard|editor-last=Goudie|editor-first=A.S.|editor-link=Andrew Goudie (geographer)|encyclopedia=Encyclopedia of Geomorphology|title= Sheet erosion, sheet flow, sheet wash|year=2004|pages=947–949|publisher=Routledge}}</ref> savanna plains<ref name=cotton1961>{{Cite journal|title=The Theory of Savanna Planation |journal=Geography |last=Cotton |first=C.A.|url=https://www.jstor.org/stable/40565228 |issue=2 |volume=46 |pages=89–101 |year=1961 |jstor=40565228 |author-link=Charles Cotton (geologist)}}</ref> and semi-arid plains.<ref>{{Cite journal|title=The role of surface water redistribution in an area of patterned vegetation in a semi-arid environment, south-west Niger |url=http://oar.icrisat.org/8077/1/Journal%20of%20Hydrology_198-1-4_1-29_1997.pdf|volume=198|pages=1–29|issue=1–4 |last1=Bromley |first1=J. |journal=Journal of Hydrology |last2=Brouwer |first2=J. |year=1997 |last3=Barker |first3=A.P. |last4=Gaze |first4=S.R. |last5=Valentine |first5=C.|doi=10.1016/S0022-1694(96)03322-7 |bibcode=1997JHyd..198....1B }}</ref> Water moving fairly uniformly with a similar thickness over a surface is called sheet flow, and is the cause of sheet erosion.<ref name=Govers/> Sheet erosion implies that any flow of water that causes the erosion is not canalized.<ref name=Govers/> If a hillslope surface contains many irregularities, sheet erosion may give way to erosion along small channels called rills, which can then converge forming gullies.<ref name=Govers/><ref name=britannica/> However, sheet erosion may occur despite some limited unevenness in the sheet flow arising from clods of earth, rock fragments, or vegetation.<ref name=Govers/>

Sheet erosion occurs in two steps. First, rainsplash dislodges small particles of the substrate and then the particles are carried away, usually short distances, by a thin and uniform layer of water (sheet flow).<ref name=britannica>{{cite web |url=https://www.britannica.com/science/sheet-erosion |title=Sheet erosion – Britannica Online Encyclopedia |publisher=Britannica.com |access-date=26 September 2018}}</ref> Transport by the sheet flow is usually over small distances, meaning that sheet erosion is a low magnitude process.<ref name=britannica/><ref name=Hogg1982>{{cite journal |last1=Hogg |first1=Susan E. |date=1982 |title=Sheetflood, sheet wash, sheet flow, or ... ?|journal=Earth-Science Reviews |volume=18 |issue=1 |pages=59–76 |doi= 10.1016/0012-8252(82)90003-4|bibcode=1982ESRv...18...59H }}</ref> However, the frequency over time with which this occurs may be high, compensating for the small change observed in each individual episode of sheet erosion.<ref name=Hogg1982/> A sheetflood can be distinguished from an ordinary sheet flow by its much greater magnitude and much lesser frequency.<ref name=Hogg1982/> Sheetfloods have been associated by various scientists with a number of causes, including high-intensity rain, low relief, lack of vegetation, low permeability of the substrate, strong weather contrast between seasons, slope form and climate change. Sheetfloods are commonly turbulent while sheetflow may be laminar or turbulent.<ref name=Hogg1982/>

Sheet erosion is common in recently ploughed fields and bare ground where the substrate, typically soil, is not consolidated.<ref name=britannica/> The resulting loss of material by sheet erosion may result in the destruction of valuable topsoils.<ref name=britannica/> Tough grass, such as vetiver, hinders the development of sheet flow.<ref>{{cite book |last=Pitty |first=A.F. |date=1971 |title=Introduction to Geomorphology |url=https://archive.org/details/introductiontoge0000pitt|url-access=registration |location=London |publisher=Methuen |page=[https://archive.org/details/introductiontoge0000pitt/page/526 526] }}</ref> The sheet erosion caused by a single rainstorm may account for the loss of up to hundred tons of small particles in an acre.<ref name=britannica/>

It has been argued that in the late Neoproterozoic Era, sheet erosion was a dominant erosion process due to the lack of plants on land.<ref name=Karna1993>{{cite journal |last1=Lidmar-Bergström |first1=Karna |author-link1=Karna Lidmar-Bergström |date=1993 |title=Denudation surfaces and tectonics in the southernmost part of the Baltic Shield |journal=Precambrian Research |volume=64 |issue= 1–4|pages=337–345 |doi= 10.1016/0301-9268(93)90086-H|bibcode=1993PreR...64..337L }}</ref> As such, sheet erosion may have contributed to shaping important landforms like the Sub-Cambrian peneplain that covers much of the Baltic Shield.<ref name=Karna1993/>

==References== {{reflist}}

Category:Erosion