Editing Subterranean river (section)

{{short description|River that runs wholly or partly beneath the ground surface}}
[[File:Burger OtokKriznaJama.jpg|thumb|upright=1.3|A subterranean river in the [[Cross Cave]] system of [[Slovenia]]. (Scale shown by people in photograph.)]]
A '''subterranean river''' (also known as an '''underground river''') is a [[river]] or [[watercourse]] that runs wholly or partly beneath the [[land|ground]], one where the riverbed does not represent the surface of the Earth.<ref>{{Cite web |last=Sosa |first=Jeff |date=2024-06-21 |title=What is a underground river called? |url=https://www.ncesc.com/geographic-faq/what-is-a-underground-river-called/ |access-date=2025-02-12 |website=Geographic FAQ Hub: Answers to Your Global Questions |language=en-US}}</ref> It is distinct from an [[aquifer]], which may flow like a river but is contained within a [[Permeable rock|permeable]] layer of rock or other unconsolidated materials. A river flowing below ground level in an open [[gorge]] is not classed as subterranean.<ref>[https://archive.org/details/cu31924013977560 William Herbert Hobbs, ''Earth Features and Their Meaning: An Introduction to Geology for the Student and the General Reader'', Macmillan, 1912, pages 182 and 189.]</ref>

Some natural rivers may be entirely subterranean, collecting in and flowing through [[cave]] systems. In [[karst topography]], rivers that originate above ground can disappear into [[sinkhole]]s, continuing underground until they reappear on the surface downstream, possibly having merged with other subterranean rivers. The longest subterranean river in the world is the [[Sistema Sac Actun]] cave system in Mexico.<ref>"Underwater cave is the world’s biggest", Mexico Daily News, January 15, 2018, https://mexiconewsdaily.com/news/underwater-cave-is-worlds-biggest/ {{Webarchive|url=https://web.archive.org/web/20181106151230/https://mexiconewsdaily.com/news/underwater-cave-is-worlds-biggest/ |date=2018-11-06 }}</ref>

Subterranean rivers can also be the result of covering over a river or diverting its flow into [[culvert]]s, usually as part of [[urban development]].<ref name="heggen">Richard J. Heggen: ''[http://www.unm.edu/~rheggen/UndergroundRivers.html Underground Rivers from the River Styx to the Rio San Buenaventura with Occasional Diversions] {{Webarchive|url=https://web.archive.org/web/20160721162218/http://www.unm.edu/~rheggen/UndergroundRivers.html |date=2016-07-21 }}'', University of New Mexico.</ref> Reversing this process is known as [[daylighting (streams)|"daylighting"]] a watercourse and is a major form of visible river restoration. Successful examples include the [[Cheonggyecheon]] in the centre of [[Seoul]].<ref>{{cite news |first= Andrew C. |last= Revkin |title= Rolling Back Pavement to Expose Watery Havens |url= https://www.nytimes.com/2009/07/17/world/asia/17daylight.html?_r=1 |work= [[New York Times]] |date=16 July 2009|access-date=16 March 2010}}</ref><ref>{{cite news 
 | first =Donald
 | last =Kirk
 | url =http://www.csmonitor.com/2005/1013/p07s01-woap.html
 | title =Seoul peels back concrete to let a river run freely once again
 | work =World>Asia Pacific
 | publisher =The Christian Science Monitor 
 | date =2005-10-13
 | access-date =2006-08-21
}}</ref>

Some fish (colloquially known as [[cavefish]]) and other [[troglobite]] organisms are adapted to life in subterranean rivers and lakes.<ref>William B. White and David C. Culver (eds), ''Encyclopedia of Caves'', 2nd ed, Academic Press, 2012, {{ISBN|0123838339}}, [https://books.google.com/books?id=aH3ymyEURHoC&pg=PA468 p. 468.]</ref>

Examples of subterranean rivers [[#Mythology_and_literature|also occur]] in mythology and literature.