River that runs wholly or partly beneath the ground surface
A subterranean river in theCross Cave system ofSlovenia. (Scale shown by people in photograph.)
Asubterranean river (also known as anunderground river) is ariver orwatercourse that runs wholly or partly beneath theground, one where the riverbed does not represent the surface of the Earth.[1] It is distinct from anaquifer, which may flow like a river but is contained within apermeable layer of rock or other unconsolidated materials. A river flowing below ground level in an opengorge is not classed as subterranean.[2]
Some natural rivers may be entirely subterranean, collecting in and flowing throughcave systems. Inkarst topography, rivers that originate above ground can disappear intosinkholes, continuing underground until they reappear on the surface downstream, possibly having merged with other subterranean rivers. The longest subterranean river in the world is theSistema Sac Actun cave system in Mexico.[3]
Subterranean rivers can also be the result of covering over a river or diverting its flow intoculverts, usually as part ofurban development.[4] Reversing this process is known as"daylighting" a watercourse and is a major form of visible river restoration. Successful examples include theCheonggyecheon in the centre ofSeoul.[5][6]
Some fish (colloquially known ascavefish) and othertroglobite organisms are adapted to life in subterranean rivers and lakes.[7]
Examples of subterranean riversalso occur in mythology and literature.
The cave ofsource of the Buna can be entered by boat and dived through a cave system serving as an effluence of theZalomka.ThePuerto Princesa cave can be entered by boat.Devil's Throat Cave subterranean river from above
There are many natural examples of subterranean rivers. Among them:
In many cities there are natural streams which have been partially or entirely built over. Such man-made examples of subterraneanurban streams are too numerous to list, but notable examples include:
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