Examine individual changes

'{{wiktionarypar|loess}} {{about|the geologic material|the statistical technique|local regression}} [[Image:ArgentinaLoess.JPG|right|thumb|250px|An [[outcrop]] of ''loess'' in [[Patagonia]], [[Argentina]].]] '''Loess''' ({{pron-en|ˈloʊ.əs}}, {{IPA-en|lʌs|}}, or {{IPA-en|lɛs|}}) is an [[aeolian processes|aeolian]] sediment formed by the accumulation of wind-blown [[silt]] and lesser and variable amounts of [[sand]] and [[clay]]. ''Loess'' sometimes refers these deposits and the [[soil]] derived from them. ==Properties== [[Image:Loess landscape china.jpg|thumb|left|Loess near [[Hunyuan]], [[Shanxi]] province, [[China]].]] Loess is [[homogeneous]], [[porous]], [[friable]], pale yellow or [[buff]], slightly [[coherent]], typically non-[[stratified]] and often [[calcareous]].<ref>Richthofen, F. von. 1882. On the mode of origin of the loess. [[The Geological Magazine]], Decade II, 9(7):293-305.</ref> Loess grains are [[Rounding (sediment)|angular]] with little polishing or rounding of hundreds of square kilometers and tens of meters thick. In several areas of the world, loess [[ridge]]s have formed that are aligned with the [[prevailing wind]]s during the last [[glacial maximum]]. These are called '''[[paha (landform)|paha]] ridges''' in America and '''greda ridges''' in [[Europe]]. . ==Etymology== ''Loess'' comes from the [[German language|German]] ''Löss'' or ''Löß'', and ultimately from [[Swiss German]] ''lösch'' meaning ''loose'' as named by [[peasants]] and [[mason]]s along the [[Rhine Valley]]. ==Formation== ===Glacial=== Glacial loess is derived from dry [[glacier|glacial]] deposits which are highly susceptible to winnowing of their [[silt]]s and [[clay]]s by the wind. These particles are then deposited downwind. The loess deposits found along both sides of the [[Mississippi River Alluvial Valley]] are a classic example of glacial loess<ref>Bettis, E.A., III, D.R. Muhs, H.M. Roberts, and A.G. Wintle, 2003, [http://esp.cr.usgs.gov/info/eolian/Bettis2003QSR.pdf ''Last glacial loess in the conterminous U.S.A.''] [[Quaternary Science Reviews]]. vol. 22, pp. 1907-1946.</ref><ref>Muhs, D.R., and E.A. Bettis, III, 2003, [http://esp.cr.usgs.gov/info/eolian/MuhsBettis2003GSAsp370.pdf ''Quaternary loess-paleosol sequences as examples of climate-driven sedimentary extremes.''] [[Geological Society of America]] Special Paper no. 370, pp. 53-74.</ref> ===Non-glacial=== Non-glacial loess can originate from from [[desert]]s, [[dune field]]s, [[playa lake]]s, and [[volcanic ash]]. Some types of nonglacial loess are:<ref>Iriondo, M.H., and D.M. Krohling, 2007, [http://adsabs.harvard.edu/abs/2007SedG..202..352I ''Non-classical types of loess.''] Sedimentary Geology. vol. 202, no. 3, pp. 352-368.</ref> * [[Volcanic]] loess in [[Ecuador]] and [[Argentina]]. * [[Tropical loess]] in [[Argentina]], [[Brazil]] and [[Uruguay]]. * [[Gypsum]] loess in [[Spain]]. * [[Tradewind]] loess in [[Venezuela]] and [[Brazil]] * [[Anticyclonic]] loess in [[Argentina]]. The thick Chinese loess deposits are non-glacial loess having been blown in from deserts in northern [[China]].<ref>Ding, Z., and J. Sun, 1999, ''Changes in Sand Content of Loess Deposits along a North–South Transect of the Chinese Loess Plateau and the Implications for Desert Variations.'' [[Quaternary Research]]. vol. 52, pp. 56–62.</ref> The loess covering the [[Great Plains]] of [[Nebraska]], [[Kansas]], and [[Colorado]] is non-glacial desert loess. Non-glacial desert loess is also found in [[Australia]].<ref>{{cite journal|last=Haberlah|first=D|year=2007|title=A call for Australian loess|journal=AREA|volume=39 |issue=2|pages= 224–229|doi=10.1111/j.1475-4762.2007.00730.x}}</ref> and [[Africa]]<ref>Muhs, D.R., and E.A. Bettis, III, 2003, [http://esp.cr.usgs.gov/info/eolian/MuhsBettis2003GSAsp370.pdf ''Quaternary loess-paleosol sequences as examples of climate-driven sedimentary extremes.''] [[Geological Society of America]] Special Paper no. 370, pp. 53-74.</ref> ==Fertility== Loess tends to develop into highly rich soils. Under appropriate climatic conditions it is some of the most agriculturally productive terrain in the world.<ref>{{cite book|last=Getis|first=Arthur|coauthors=Judith Getis and Jerome D. Fellmann|title=Introduction to Geography, Seventh Edition|year=2000 |publisher=[[McGraw Hill]]|isbn=0-697-38506-X |pages= 99}}</ref> Soils underlain by loess tend to be excessively drained. The fine grains [[weathering|weather]] rapidly due to their large surface area making soils derived from loess very rich. One theory states that the fertility of loess soils is due largely to [[electron exchange capacity]] (the ability of plants to absorb nutrients from the soil) and [[porosity]] (the air-filled space in the soil). The fertility of Loess is not due to organic matter content, which tends to be rather low unlike tropical soils, which derive their fertility almost wholly from on organic matter. Even well managed loess [[farmland]] can experience dramatic erosion of well over 2.5 kg per square meter per year. Although in geological time loess has an incredible rate of erosion, in a more human time scale loess is durable and resistant to maltreatment. In China [[Loess Plateau|loess deposits]] along the [[Yellow River]] have been farmed and have produced phenomenal yields for over one thousand years. A large amount of the credit for this goes to the farmers; Chinese farmers were the first to practice active [[erosion control]]. The largest deposit of loess in the United States, the [[Loess Hills]] along the border of [[Iowa]] and [[Nebraska]], has survived intensive farming and poor farming practices. For almost 150 years this loess deposit was farmed with [[mouldboard plough]]s and [[fall tilled]], both intensely erosive. At times it suffered erosion rates of over 10 kilograms per square meter per year. Today this loess deposit is worked as [[low till]] or [[no till]] in all areas and is aggressively [[terrace (agriculture)|terraced]]. ==Sites== [[Image:Loessreef.jpg|250px|right|thumb|''Loess reefs'' in [[Hungary]].]] The [[Loess Hills]] of [[Iowa]] owes their fertility to the [[prairie]] [[topsoil]]s built by 10,000 years of post-glacial accumulation of organic-rich [[humus]] as a consequence of a persistent [[grassland]] [[biome]]. When the valuable [[Soil_horizon#A_Horizon|A-horizon]] topsoil is eroded or degraded, the underlying loess soil is infertile, and requires the addition of [[fertilizer]] in order to support [[agriculture]]. The loess along the [[Mississippi River]] near [[Vicksburg]], [[Mississippi]] consist of three layers. The ''Peoria Loess'', ''Sicily Island Loess'', and ''Crowley's Ridge Loess'' accumulated at different periods of time during the [[Pleistocene]]. Ancient soils, called [[paleosol]]s, have developed in the top of the Sicily Island Loess and Crowley's Ridge Loess. The lowermost loess, the Crowley's Ridge Loess, accumulated during the late [[Illinoian Stage]]. The middle loess, Sicily Island Loess, accumulated during early [[Wisconsin glaciation|Wisconsin Stage]]. The uppermost loess, the Peoria Loess, in which the modern soil has developed, accumulated during the late Wisconsin Stage. Animal remains include terrestrial [[gastropod]]s and [[mastodon]]s<ref name="MillerOthers1">Miller, B.J., G.C. Lewis, J.J. Alford, and W.J. Day, 1985, Loesses in Louisiana and at Vicksburg, Mississippi. Guidebook, Friends of the Pleistocene Field Trip, 12-14 April, 1985. [[LA Agricultural Experimental Station]], [[Louisiana State University]], [[Baton Rouge]], [[Louisiana]]. 126 pp.</ref> Loess soil forms sharp hills east of the [[Mississippi River]] and [[Yazoo River]] in western [[Mississippi]] north and south of [[Vicksburg, Mississippi|Vicksburg]]. These deposits are more than 30 m thick (comparable to those in Iowa) immediately above the river valleys, to which they are sub-parallel, and thin to trace thickness within 40&nbsp;km to the east. Streams and [[gulley]]s are incised very deeply and sharply between the linear loess ridges making topography very important in the conduct of military operations for the [[Vicksburg Campaign]]. [[Hungary]] has several areas that are covered by loess. At locations such as [[Dunaújváros]] and [[Balatonakarattya]], loess walls are exposed as '''loess reefs'''. Similar formations exist in [[Bulgaria]] on the south bank of the [[Danube]]. The central part of [[Belgium]] is covered by thick loess stacks. [[Neanderthal]] artifacts were found within the soils between the loess layers of the [[Veldwezelt-Hezerwater]]. ==References== {{reflist}} == External links == * 2006, [http://www.semp.us/publications/biot_printview.php?BiotID=357 ''The Secret of China’s Vast Loess Plateau''] [[Suburban Emergency Management Project]], [[Chicago]], [[Illinois]]. * 2007, [http://www.ufz.de/index.php?en=15536 ''New European Loess Map.''] [[Helmholtz Centre for Environmental Research]], [[Leipzig]], [[Germany]]. * [http://www.museum.state.il.us/exhibits/larson/loess.html ''Glacial Deposits: Loess and Till.''] [[Illinois State Museum]], [[Springfield]], [[Illinois]]. * Briedis. C.A., 2006, [http://www.isgs.uiuc.edu/sections/quat/loessthick-map.shtml ''Loess Thickness Map (of Illinois).''] [[Illinois State Geological Survey]], [[Champaign]], [[Illinois]]. * Gill, T.E., A. Warren, and J.E. Stout, 2008, [http://www.lbk.ars.usda.gov/wewc/biblio/bar.htm ''The Bibliography of Aeolian Research.''] [[Cropping Systems Research Laboratory]], [[U.S. Department of Agriculture]], [[Lubbock]], [[Texas]]. * Heinrich, P.V., 2008, [http://www.lgs.lsu.edu/deploy/uploads/Loess%20Map%20of%20LA.pdf ''Loess map of Louisiana.''], Public Information Series. no. 12, [[Louisiana Geological Survey]], [[Baton Rouge]], [[Louisiana]]. * Prior, J.C., and D.J. Quade, nd, [http://www.igsb.uiowa.edu/Browse/loess/loess.htm ''The Loess Hills: A Geologic View.''] [[Iowa Geological Survey]], [[Department of Natural Resources]], [[Iowa City]], [[Iowa]]. * [[U.S. Geological Survey]], 1999, [http://pubs.usgs.gov/info/loess/ ''Geology of the Loess Hills, Iowa''] * [[U.S. Geological Survey]], 2006, [http://esp.cr.usgs.gov/info/eolian/task2.html ''Eolian History of North America''] Why is loess important to study? * [http://www.nfinity.com/~exile/loesspg.htm ''The Loess Hills of Western Iowa''] [[Category:German loanwords]] [[Category:Glaciology]] [[Category:Sedimentary rocks]] [[Category:Sediments]] [[Category:Types of soil]] [[Category:Aeolian landforms]] [[be:Лёс, горная парода]] [[ca:Loess]] [[cs:Spraš]] [[da:Löss]] [[de:Löss]] [[et:Löss]] [[es:Loess]] [[eo:Leŭso]] [[eu:Loess]] [[fa:بادرفت]] [[fr:Lœss]] [[hi:लोयस]] [[it:Löss]] [[lt:Liosas]] [[li:Löss]] [[hu:Lösz]] [[nl:Löss]] [[nds-nl:Löss]] [[ja:黄土]] [[no:Løss]] [[pl:Less]] [[pt:Loess]] [[ro:Loess]] [[ru:Лёсс]] [[fi:Lössi]] [[sv:Lössjord]] [[zh:黃土]]'