Underground lake within Cross Cave in Slovenia, one of 22 such lakes

An underground lake or subterranean lake is a lake underneath the surface of the Earth. Most naturally occurring underground lakes are found in areas of karst topography,[1][2] where limestone or other soluble rock has been weathered away, leaving a cave where water can flow and accumulate.

Natural underground lakes are an uncommon hydrogeological feature. More often, groundwater gathers in formations such as aquifers or springs.

The largest subterranean lake in the world is in Dragon's Breath Cave in Namibia,[3] with an area of almost 2 hectares (5 acres);[4] the second largest is The Lost Sea, located inside Craighead Caverns in Tennessee, United States, with an area of 1.8 hectares (4.4 acres) [5]

Characteristics

An underground lake is any body of water that is similar in size to a surface lake and exists mostly or entirely underground; though, a precise scientific definition of what may be considered a "lake" is not yet well-established.[6] Underground lakes could be classified as either “lakes” or "ponds", depending on characteristics of size, such as exposed surface area and/or depth.

The rarity of naturally-occurring underground lakes can be attributed to the way water behaves underground. Below the surface of the Earth, pressure exterted on water increases, causing it to be absorbed into the ground. The boundary at which there is sufficient sub-terranean pressure to completely saturate the ground with water is called the water table. The area above the water table is called the “unsaturated zone,” while the area below it is called the “saturated zone” [2].[7] In the saturated zone, pressure is the primary force driving the flow of water. Lakes form primarily under the force of gravity – water is pulled down to the lowest point in an area, and gathers into a lake. Any water below the water table will be under pressure, and so does not form a lake; instead, it forms an aquifer.

Naturally-occurring underground lakes can form in Karst areas, where the weathering of soluble rocks leaves behind caverns and other openings in the earth.[2] Surface water can find its way underground through these openings[8] and pool up in larger caverns to form lakes.

Underground lakes can be formed by human processes, such as the flooding of mines. Two examples of these are lakes found in the slate mines at Blaenau Ffestiniog, such as Croesor quarry,[9][10] and a lake in the Hallein Salt Mine in Austria.[11]

Examples

See also

References

  1. ↑ Palmer, Arthur N. (2007). Cave geology. Dayton, Ohio: Cave Books. ISBN 978-0-939748-66-2. OCLC 74965086.
  2. 1 2 3 Earle, Steven (September 2015). Physical Geology (2nd ed.). pp. ch. 14.2: Groundwater Flow. Retrieved 29 September 2022.
  3. ↑ Kelly, Daniel (24 January 2014). "Dragon's Breath Cave Holds the World's Largest Underground Lake". Lake Scientist. Archived from the original on 1 March 2015. Retrieved 31 May 2016.
  4. ↑ "Dragon's Breath Cave: Namibia has the worlds largest underground lake". Wanted in Africa. 12 June 2020. Retrieved 29 September 2022.
  5. ↑ "History of the Lost Sea". The Lost Sea. Retrieved 29 September 2022.
  6. ↑ Lane, Robert K. "Lake". Encyclopedia Britannica. Retrieved 29 September 2022.
  7. ↑ "Water Table". National Geographic. Retrieved 29 September 2022.
  8. ↑ Parise, M.; Gunn, J. (2007). "Natural and anthropogenic hazards in karst areas: an introduction". Geological Society, London, Special Publications. The Geological Society of London. 279: 1–3. doi:10.1144/sp279.1. S2CID 130950517. Retrieved 29 September 2022.
  9. ↑ Johnson, Rob (18 December 2021). "Croesor Rhosydd Through Trip". Mountaineering Instruction and Courses in Snowdonia. Retrieved 2 October 2022.
  10. ↑ "Croesor Rhosydd Through Trip". ukBouldering.com. 2 June 2002. Archived from the original on 7 February 2012.
  11. ↑ "Discover and Experience". Salz Welten. Retrieved 2 October 2022.

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