View source for Oxbow lake

{{Short description|U-shaped lake or pool left by an ancient river meander}}
{{Other uses}}
[[File:Nowitna river.jpg|thumb|upright=1.5|This picture of the [[Nowitna River]] in Alaska shows two oxbow lakes – a short one at the bottom of the picture and a longer, more curved one at the middle-right. The picture also shows that a third oxbow lake is probably in the making: the isthmus or bank in the centre of the most prominent meander is very narrow &ndash; much narrower than the width of the river; eventually, the two sections of river on either side of an isthmus like that tend to break through and create a new, straighter course; a new river bank then starts to accumulate, sealing off the meander and leaving another oxbow lake.]]
An '''oxbow lake''' is a U-shaped [[lake]] or [[stream pool|pool]] that forms when a wide [[meander]] of a [[river]] is [[meander cutoff|cut off]], creating a free-standing body of water. The word "oxbow" can also refer to a U-shaped bend in a river or stream, whether or not it is cut off from the main stream.<ref>{{cite web|url = http://www.askoxford.com/concise_oed/oxbow?view=uk|archive-url = https://web.archive.org/web/20070930004915/http://www.askoxford.com/concise_oed/oxbow?view=uk|url-status = dead|archive-date = September 30, 2007|title = Oxbow|publisher = [[Oxford English Dictionary]]|access-date = 2009-10-27}}</ref><ref>{{cite web|url = http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=oxbow|title = Oxbow|publisher = [[Merriam–Webster]]|access-date = 2009-10-27}}</ref>
In [[South Texas]], oxbows left by the [[Rio Grande]] are called ''[[resaca (channel)|resaca]]s''.  In [[Australia]], oxbow lakes are called [[billabong]]s.
== Geology ==
[[File:Meander Oxbow development.svg|thumb|upright|A meander develops into an oxbow lake]]
An oxbow lake forms when a meandering river erodes through the neck of one of its [[meander]]s. This takes place because meanders tend to grow and become more curved over time. The river then follows a shorter course that bypasses the meander.<ref name=NatGeo>{{cite web |last1=Rutledge |first1=Kim |last2=Ramroop |first2=Tara |last3=Boudreau |first3=Diane |last4=McDaniel |first4=Melissa |last5=Teng |first5=Santani |last6=Sprout |first6=Erin |last7=Costa |first7=Hilary |last8=Hall |first8=Hilary |last9=Hunt |first9=Jeff |title=Oxbow lake |date=10 June 2011 |url=https://www.nationalgeographic.org/encyclopedia/oxbow-lake/ |publisher=National Geographic |access-date=26 September 2021}}</ref> The entrances to the abandoned meander eventually silt up, forming an oxbow lake.<ref name=ConstantineEtal2010>{{cite journal |last1=Constantine |first1=José Antonio |last2=Dunne |first2=Thomas |last3=Piégay |first3=Hervé |last4=Mathias Kondolf |first4=G. |title=Controls on the alluviation of oxbow lakes by bed-material load along the Sacramento River, California |journal=Sedimentology |date=February 2010 |volume=57 |issue=2 |pages=389–407 |doi=10.1111/j.1365-3091.2009.01084.x|bibcode=2010Sedim..57..389C |s2cid=129166672 }}</ref> Because oxbow lakes are stillwater lakes, with no current flowing through them, the entire lake gradually silts up, becoming a bog or swamp and then evaporating completely.<ref name=NatGeo/><ref>{{cite journal |last1=Kirschner |first1=Alexander K. T. |last2=Riegl |first2=Bernhard |last3=Velimirov |first3=Branko |title=Degradation of Emergent and Submerged Macrophytesin an Oxbow Lake of an Embanked Backwater System: Implications for the Terrestrialization Process |journal=International Review of Hydrobiology |date=2001 |volume=86 |issue=4–5 |pages=555–571 |doi=10.1002/1522-2632(200107)86:4/5<555::AID-IROH555>3.0.CO;2-9}}</ref>
When a river reaches a low-lying plain, often in its final course to the [[sea]] or a [[lake]], it meanders widely. In the vicinity of a [[river]] bend, [[deposition (sediment)|deposition]] occurs on the [[wikt:convex|convex]] bank (the bank with the smaller radius). In contrast, both lateral [[erosion]] and undercutting occur on the [[Cut bank (geology)|cut bank]] or [[wikt:convex|concave]] bank (the bank with the greater radius). Continuous deposition on the convex bank and erosion of the concave bank of a meandering river cause the formation of a very pronounced [[meander]] with two concave banks getting closer. The narrow neck of land between the two neighboring concave banks is finally cut through, either by lateral erosion of the two concave banks or by the strong currents of a [[flood]]. When this happens a new, straighter river [[Channel (geography)|channel]] develops—and an abandoned meander loop, called a [[meander cutoff|cutoff]], forms. When deposition finally seals off the cutoff from the river channel, an oxbow lake forms. This process can occur over a time from a few years to several decades, and may sometimes become essentially static.<ref name=ConstantineEtal2010/>
Gathering of erosion products near the concave bank and transporting them to the convex bank is the work of the [[secondary flow]] across the floor of the river in the vicinity of a river bend. The process of deposition of silt, sand and gravel on the convex bank is clearly illustrated in [[point bar]]s.<ref name="hickin">{{cite book| last = Hickin| first = Edward J| contribution = Meandering Channels| year = 2002| title =  Encyclopedia of Sediments and Sedimentary Rocks| editor-last = Middleton| editor-first = Gerard V.| isbn = 1-4020-0872-4| page = 432| place = New York| publisher = Springer}}</ref>
The effect of the secondary flow can be demonstrated using a circular bowl.  Partly fill the bowl with water and sprinkle dense particles such as sand or rice into the bowl. Set the water into circular motion with one hand or a spoon. The dense particles quickly sweep into a neat pile in the center of the bowl. This is the mechanism that leads to the [[Point bar#Formation|formation of point bars]] and contributes to the formation of oxbow lakes. The primary flow of water in the bowl is circular and the streamlines are concentric with the side of the bowl. However, the [[Secondary flow#Circular flow in a bowl or cup|secondary flow]] of the [[boundary layer]] across the floor of the bowl is inward toward the center. The primary flow might be expected to fling the dense particles to the perimeter of the bowl, but instead the secondary flow sweeps the particles toward the center.<ref>{{cite journal|last=Bowker|first=Kent A.|date=1988|title=Albert Einstein and Meandering Rivers|journal=Earth Science History|volume=1|issue=1|page=45 |doi=10.17704/eshi.7.1.yk72n55q84qxu5n6 |bibcode=1988ESHis...7...45B |url=http://www.searchanddiscovery.net/documents/Einstein/albert.htm|access-date=2016-07-01}}
</ref>
The curved path of a river around a bend makes the water's surface slightly higher on the outside of the bend than on the inside. As a result, at any elevation within the river, water pressure is slightly greater near the outside of the bend than on the inside. A pressure gradient toward the convex bank provides the [[centripetal force]] necessary for each parcel of water to follow its curved path.
The [[boundary layer]] that flows along the river floor does not move fast enough to balance the pressure gradient laterally across the river. It responds to this pressure gradient, and its velocity is partly downstream and partly across the river toward the convex bank.<ref name="hickin" /><ref>{{cite journal|last1=Chant|first1=R. J.|title=Secondary circulation in a region of flow curvature: Relationship with tidal forcing and river discharge|journal=Journal of Geophysical Research|date=2002|volume=107|issue=C9|pages=14-1–14-11|doi=10.1029/2001JC001082|bibcode=2002JGRC..107.3131C}}</ref>  As it flows along the floor of the river, it sweeps loose material toward the convex bank. This flow of the boundary layer is significantly different from the speed and direction of the primary flow of the river, and is part of the river's [[Secondary flow#River bends|secondary flow]].
[[File:Oxbow lake.jpg|thumb|upright=1.25|A Horseshoe or oxbow lake near [[Hughes, Arkansas|Hughes]], [[Arkansas]], on the border between Arkansas and [[Mississippi]]. The bulges in the border reflect changes in the course of the river; when the river shifted its course and cut off the former channel, the border remained unchanged.]]
River flood plains that contain rivers with a highly sinuous platform are populated by longer oxbow lakes than those with low [[sinuosity]].  This is because rivers with high sinuosity have larger meanders, and greater opportunity for longer lakes to form. Rivers with lower sinuosity are characterized by fewer cutoffs and shorter oxbow lakes due to the shorter distance of their meanders.<ref>{{cite journal|last1=Constantine|first1=J. A.|last2=Dunne|first2=T.|title=Meander cutoff and the controls on the production of oxbow lakes|journal=Geology|date=2008|volume=36|issue=1|pages=23–26|doi=10.1130/G24130A.1|bibcode=2008Geo....36...23C}}</ref>
== Oxbow lake ecology ==
[[File:Red Deer on the Upper Taieri Watermeadow - panoramio.jpg|thumb|Oxbow lakes on New Zealand's [[Taieri River]] have been converted into [[water meadow]]s.]]
Oxbow lakes serve as important wetland ecosystems. In the United States, oxbow lakes serve as the primary habitat for [[Nyssa aquatica|water tupelo]] and the iconic [[Taxodium distichum|bald cypress]].<ref name="Shankman1994">{{cite journal |last1=Shankman |first1=David |last2=Kortright |first2=Rosa Maria |title=Hydrogeomorphic conditions limiting the distribution of baldcypress in the southeastern United States |journal=Physical Geography |date=May 1994 |volume=15 |issue=3 |pages=282–295 |doi=10.1080/02723646.1994.10642517}}</ref> The numerous oxbow lakes of the [[Amazon River]] are a favorable habitat for the [[giant river otter]].<ref name=NatGeo/> Oxbow lakes may also be suitable locations for [[aquaculture]].<ref>{{cite journal |last1=Gupta |first1=S. |last2=Devi |first2=S.S. |year=2014 |title=Ecology of Baskandi anua, an oxbow lake of South Assam, North East India |journal=Journal of Environmental Biology |volume=35 |number=6 |pages=1101–1105 |pmid=25522512 |url=https://www.researchgate.net/publication/269769587 |access-date=26 September 2021}}</ref>
Oxbow lakes contribute to the health of a river ecosystem by trapping sediments and agricultural runoff, thereby removing them from the main river flow. However, this is destructive of the oxbow lake ecosystem itself.<ref>{{cite journal |last1=Glińska-Lewczuk |first1=Katarzyna |year=2005 |title=Oxbow lakes as biogeochemical filters for nutrient outflow from agricultural areas |journal=Dynamics and Biogeochemistry of River Corridors and Wetlands |volume=294 |pages=55–69 |url=https://www.researchgate.net/publication/294756671 |access-date=26 September 2021}}</ref> Oxbow lakes are also vulnerable to [[heavy metals|heavy metal]] contamination from industrial sources.<ref>{{cite journal |last1=Ciazela |first1=Jakub |last2=Siepak |first2=Marcin |last3=Wojtowicz |first3=Piotr |title=Tracking heavy metal contamination in a complex river-oxbow lake system: Middle Odra Valley, Germany/Poland |journal=Science of the Total Environment |date=March 2018 |volume=616-617 |pages=996–1006 |doi=10.1016/j.scitotenv.2017.10.219|pmid=29103644 |bibcode=2018ScTEn.616..996C }}</ref>
==Artificial oxbow lakes==
Oxbow lakes may be formed when a river channel is straightened artificially to improve navigation or for flood alleviation. This occurred notably on the upper [[Rhine]] in Germany in the nineteenth century.<ref>{{cite web
|url = http://www.zinke.at/Japansymp.htm|title = The New Management of Rivers and Wetlands in Central Europe|last = Zinke|first = Alexander|publisher = Zinke Environmental Consulting|date = December 17, 2000|access-date = 2009-10-27}}</ref>
An example of an entirely artificial waterway with oxbows is the [[Oxford Canal]] in England. When originally constructed, it had a very meandering course, following the contours of the land, but the northern part of the canal was straightened out between 1829 and 1834, reducing its length from approximately {{convert|91|to|77+1/2|mi|km|order=flip|abbr=on|0}} and creating a number of oxbow-shaped sections isolated from the new course.<ref>{{cite book|last = Boughey|first = Joseph|title = Hadfield's British Canals|isbn = 0-7509-1840-3|publisher = [[The History Press|Sutton Publishing]]|year = 1994}}</ref>
== Notable examples ==<!--Please keep alphabetical by name of feature-->
*Bole and Burton Round in [[West Burton, Nottinghamshire]], [[England]] are a good example of previous lakes in a close proximity to one another.
*[[Bayou Brevelle]] in [[Natchitoches Parish, Louisiana|Natchitoches Parish, United States]] was created after the [[Red River of the South]] altered its course due to the effects of the [[Great Raft]].
*[[Carter Lake (Iowa-Nebraska)|Carter Lake, United States]] was created after severe flooding in 1877 led to the Missouri River shifting approximately {{convert|1+1/4|mi|km|0|order=flip|abbr=off|spell=in}} to the southeast.
*[[Cuckmere Haven]] in [[Sussex]], [[England]] contains a widely [[meander]]ing [[river]] with many oxbow lakes, often referred to in [[physical geography]] textbooks.
*Halfmoon Lake in downtown [[Eau Claire, Wisconsin|Eau Claire, United States]] was formed due to a shift in the course of the [[Chippewa River (Wisconsin)|Chippewa River]], which now flows immediately to the south.
*[[Kanwar Lake Bird Sanctuary]], [[India]] contains rare and endangered migratory birds and is one of Asia's largest oxbow lakes.
*[[The Oxbow (Connecticut River)|The Oxbow]], a {{convert|2+1/2|mi|km|0|spell=in|order=flip|abbr=off|adj=on}} bend in the [[Connecticut River]], is disconnected at one end.
*There are many oxbow lakes alongside the Mississippi River and its tributaries.  The largest oxbow lake in North America, [[Lake Chicot]] (located near [[Lake Village, Arkansas|Lake Village, United States]]), was originally part of the [[Mississippi River]], as was Horseshoe Lake, the namesake for the town of [[Horseshoe Lake, Arkansas|Horseshoe Lake, United States]].  [[Reelfoot Lake]] in west [[Tennessee]] is another notable oxbow lake; it was formed when the [[Mississippi River]] took a new channel following the [[1811–12 New Madrid earthquakes]].
*The upper reaches of New Zealand's [[Taieri River]] has also cut a multitude of oxbow lakes in its upper course near the town of [[Paerau]]. Some of this area has been converted into [[water meadow]]s.
*[[Vynthala Lake | Vynthala Lake, Chalakudy]], [[India]] is formed from a "cutoff" of the Chalakudy River which flows nearby.
There has also been a possible oxbow lake postulated in [[List of geological features on Titan#Flumina|Saraswati Flumen]] near [[Ontario Lacus]] on Saturn's moon [[Titan (moon)|Titan]].<ref>{{Cite journal|last1=Dhingra|first1=Rajani D.|last2=Barnes|first2=Jason W.|last3=Yanites|first3=Brian J.|last4=Kirk|first4=Randolph L.|date=2018-01-01|title=Large catchment area recharges Titan's Ontario Lacus|journal=Icarus|language=en|volume=299|pages=331–338|doi=10.1016/j.icarus.2017.08.009|bibcode=2018Icar..299..331D|issn=0019-1035}}</ref>
<gallery>
File:Cole_Thomas_The_Oxbow_(The_Connecticut_River_near_Northampton_1836).jpg|''[[The Oxbow]]'', on the Connecticut River, [[Thomas Cole]]
File:SonghuaRiver ASTER 20020401.jpg|The swirls and curves of the previous courses of the  [[Songhua River]] in [[northeast China]]
File:Ox-bow meander.jpg|Early stages of formation of coastal plain oxbow lake in the [[Gower Peninsula]] of southwest [[Wales]]
File:Oxbow titan.gif|The proposed oxbow lake on Saturn's moon Titan, from [[Cassini–Huygens|Cassini]] RADAR images
</gallery>
== See also ==
{{Portal|Lakes|Wetlands}}
<!-- Please keep entries in alphabetical order & add a short description [[WP:SEEALSO]] -->
{{div col|colwidth=20em|small=yes}}
* [[Anabranch]]
* [[Bayou]]
* [[Billabong]]
* [[Point bar#Fallacy regarding formation of point bars|Fallacy regarding formation of point bars]]
* [[Resaca (channel)]]
* [[Secondary flow#River bends|Secondary flow around river bends]]
{{div col end}}
<!-- please keep entries in alphabetical order -->
==References==
{{Reflist}}
==External links==
{{Commons category|Oxbow lakes}}
*[https://web.archive.org/web/20070312145458/http://rst.gsfc.nasa.gov/Sect17/Sect17_4.html NASA Remote Sensing Tutorial: Fluvial/Deltaic/Coastal Landforms] (archived 12 March 2007)
*[http://googleearthtimemachine.blogspot.fr/2012/07/angleton-texas.html Ox Bow Lake Formation, As Seen By the Google Earth Time Machine]
{{River morphology|state=collapsed}}
{{Authority control}}
[[Category:Oxbow lakes| ]]
[[Category:Fluvial landforms]]
[[Category:Lakes by type]]
[[Category:Rivers]]