Underground lake

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Underground lake within Cross Cave in Slovenia, one of 22 such lakes Burger OtokKriznaJama.jpg
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.

Contents

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

Related Research Articles

<span class="mw-page-title-main">Cave</span> Natural underground space large enough for a human to enter

A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word cave can refer to smaller openings such as sea caves, rock shelters, and grottos, that extend a relatively short distance into the rock and they are called exogene caves. Caves which extend further underground than the opening is wide are called endogene caves.

<span class="mw-page-title-main">Karst</span> Topography from dissolved soluble rocks

Karst is a topography formed from the dissolution of soluble carbonate rocks such as limestone, dolomite, and gypsum. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. More weathering-resistant rocks, such as quartzite, can also occur, given the right conditions.

<span class="mw-page-title-main">Aquifer</span> Underground layer of water-bearing permeable rock

An aquifer is an underground layer of water-bearing material, consisting of permeable or fractured rock, or of unconsolidated materials. Aquifers vary greatly in their characteristics. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include aquitard, which is a bed of low permeability along an aquifer, and aquiclude, which is a solid, impermeable area underlying or overlying an aquifer, the pressure of which could lead to the formation of a confined aquifer. The classification of aquifers is as follows: Saturated versus unsaturated; aquifers versus aquitards; confined versus unconfined; isotropic versus anisotropic; porous, karst, or fractured; transboundary aquifer.

<span class="mw-page-title-main">Sinkhole</span> Geologically-formed topological depression

A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water enters into underground passages known as ponor, swallow hole or swallet. A cenote is a type of sinkhole that exposes groundwater underneath. Sink and stream sink are more general terms for sites that drain surface water, possibly by infiltration into sediment or crumbled rock.

<span class="mw-page-title-main">Subterranean river</span> River that runs wholly or partly beneath the ground surface

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.

An underwater environment is a environment of, and immersed in, liquid water in a natural or artificial feature, such as an ocean, sea, lake, pond, reservoir, river, canal, or aquifer. Some characteristics of the underwater environment are universal, but many depend on the local situation.

<span class="mw-page-title-main">Spring (hydrology)</span> Point at which water emerges from an aquifer to the surface

A spring is a natural exit point at which groundwater emerges out of the aquifer and flows onto the top of the Earth's crust (pedosphere) to become surface water. It is a component of the hydrosphere, as well as a part of the water cycle. Springs have long been important for humans as a source of fresh water, especially in arid regions which have relatively little annual rainfall.

<span class="mw-page-title-main">Cenote</span> Natural pit or sinkhole that exposes groundwater underneath

A cenote is a natural pit, or sinkhole, resulting when a collapse of limestone bedrock exposes groundwater. The term originated on the Yucatán Peninsula of Mexico, where the ancient Maya commonly used cenotes for water supplies, and occasionally for sacrificial offerings. The name derives from a word used by the lowland Yucatec Maya—tsʼonoʼot—to refer to any location with accessible groundwater.

Phreatic is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption.

<span class="mw-page-title-main">Vadose zone</span> Unsaturated aquifer above the water table

The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater is at atmospheric pressure. Hence, the vadose zone extends from the top of the ground surface to the water table.

Fossil water or paleowater is an ancient body of water that has been contained in some undisturbed space, typically groundwater in an aquifer, for millennia. Other types of fossil water can include subglacial lakes, such as Antarctica's Lake Vostok, and even ancient water on other planets.

<span class="mw-page-title-main">Show cave</span> Cave made accessible to the general public for guided visits

A show cave—also called tourist cave, public cave, and, in the United States, commercial cave—is a cave which has been made accessible to the public for guided visits.

<span class="mw-page-title-main">Craighead Caverns</span>

Craighead Caverns is an extensive cave system located in between Sweetwater and Madisonville, Tennessee. It is best known for containing the United States' largest and the world's second largest non-subglacial underground lake, The Lost Sea. In addition to the lake, the caverns contain an abundance of crystal clusters called anthodites, stalactites, stalagmites, and a waterfall.

A losing stream, disappearing stream, influent stream or sinking river is a stream or river that loses water as it flows downstream. The water infiltrates into the ground recharging the local groundwater, because the water table is below the bottom of the stream channel. This is the opposite of a more common gaining stream which increases in water volume farther downstream as it gains water from the local aquifer.

<span class="mw-page-title-main">Karst window</span> Unroofed portion of a cavern which reveals part of a subterranean river

A karst window, also known as a karst fenster, is a geomorphic feature found in karst landscapes where an underground river is visible from the surface within a sinkhole. In this feature, a spring emerges, then the discharge abruptly disappears into a sinkhole. The word fenster is German for 'window', as these features are windows into the karst landscape.

The Nambung River is a river in the Wheatbelt region of Western Australia, 170 kilometres (106 mi) north of Perth. The river drains an area between the towns of Cervantes and Badgingarra. In its lower reaches the Nambung River forms a chain of waterholes in the Nambung Wetlands where it disappears underground into a limestone karst system 5.5 kilometres (3 mi) from the Indian Ocean.

<span class="mw-page-title-main">Solutional cave</span> Type of cave

A solutional cave, solution cave, or karst cave is a cave usually formed in the soluble rock limestone. It is the most frequently occurring type of cave. It can also form in other rocks, including chalk, dolomite, marble, salt beds, and gypsum.

<span class="mw-page-title-main">Dragon's Breath Cave</span> Cave in the Otjozondjupa Region of Namibia

Dragon's Breath Cave is located in the Otjozondjupa Region of Namibia on private land, not accessible to the general public. The cave was discovered by Roger Ellis during a caving expedition to the area in 1986. It is named for the moist air rising from its entrance which resembled the breath of a dragon.

<span class="mw-page-title-main">Fissure</span> Long, narrow crack opening on a planetary surface

A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word fissura, which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes.

An anchialine system is a landlocked body of water with a subterranean connection to the ocean. Depending on its formation, these systems can exist in one of two primary forms: pools or caves. The primary differentiating characteristics between pools and caves is the availability of light; cave systems are generally aphotic while pools are euphotic. The difference in light availability has a large influence on the biology of a given system. Anchialine systems are a feature of coastal aquifers which are density stratified, with water near the surface being fresh or brackish, and saline water intruding from the coast at depth. Depending on the site, it is sometimes possible to access the deeper saline water directly in the anchialine pool, or sometimes it may be accessible by cave diving.

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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