Subterranean river

A subterranean river is a river or watercourse that runs wholly or partly beneath the ground, one where the riverbed does not represent the surface of the Earth. It is distinct from an aquifer, which may flow like a river but is contained within a permeable layer of rock or other unconsolidated materials. A river flowing below ground level in an open gorge is not classed as subterranean.^[1]

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 sinkholes, 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.^[2]

Subterranean rivers can also be the result of covering over a river or diverting its flow into culverts, usually as part of urban development.^[3] Reversing this process is known as "daylighting" a watercourse and is a major form of visible river restoration. Successful examples include the Cheonggyecheon in the centre of Seoul.^[4]^[5]

Some fish (colloquially known as cavefish) and other troglobite organisms are adapted to life in subterranean rivers and lakes.^[6]

Examples of subterranean rivers also occur in mythology and literature.

^ 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.
^ "Underwater cave is the world’s biggest", Mexico Daily News, January 15, 2018, https://mexiconewsdaily.com/news/underwater-cave-is-worlds-biggest/
^ Richard J. Heggen: Underground Rivers from the River Styx to the Rio San Buenaventura with Occasional Diversions Archived 2016-07-21 at the Wayback Machine, University of New Mexico.
^ Revkin, Andrew C. (16 July 2009). "Rolling Back Pavement to Expose Watery Havens". New York Times. Retrieved 16 March 2010.
^ Kirk, Donald (2005-10-13). "Seoul peels back concrete to let a river run freely once again". World>Asia Pacific. The Christian Science Monitor. Retrieved 2006-08-21.
^ William B. White and David C. Culver (eds), Encyclopedia of Caves, 2nd ed, Academic Press, 2012, ISBN 0123838339, p. 468.

[1] 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.

[2] "Underwater cave is the world’s biggest", Mexico Daily News, January 15, 2018, https://mexiconewsdaily.com/news/underwater-cave-is-worlds-biggest/

[heggen-3] Richard J. Heggen: Underground Rivers from the River Styx to the Rio San Buenaventura with Occasional Diversions Archived 2016-07-21 at the Wayback Machine, University of New Mexico.

[4] Revkin, Andrew C. (16 July 2009). "Rolling Back Pavement to Expose Watery Havens". New York Times. Retrieved 16 March 2010.

[5] Kirk, Donald (2005-10-13). "Seoul peels back concrete to let a river run freely once again". World>Asia Pacific. The Christian Science Monitor. Retrieved 2006-08-21.

[6] William B. White and David C. Culver (eds), Encyclopedia of Caves, 2nd ed, Academic Press, 2012, ISBN 0123838339, p. 468.

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