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 (also known as a 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, the amount of pressure exerted on groundwater increases, causing it to be absorbed into the soil. 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 becomes 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] and a lake in the Hallein Salt Mine in Austria. [10]

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">Water table</span> Top of a saturated aquifer, or where the water pressure head is equal to the atmospheric pressure

The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the locality. It can also be simply explained as the depth below which the ground is saturated.

<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.

<span class="mw-page-title-main">Groundwater</span> Water located beneath the ground surface

Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table. Groundwater is recharged from the surface; it may discharge from the surface naturally at springs and seeps, and can form oases or wetlands. Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.

<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.

The Floridan aquifer system, composed of the Upper and Lower Floridan aquifers, is a sequence of Paleogene carbonate rock which spans an area of about 100,000 square miles (260,000 km2) in the southeastern United States. It underlies the entire state of Florida and parts of Alabama, Georgia, Mississippi, and South Carolina.

<span class="mw-page-title-main">Craighead Caverns</span> Cave system in Tennessee, United States

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">Groundwater recharge</span> Groundwater that recharges an aquifer

Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in the vadose zone below plant roots and is often expressed as a flux to the water table surface. Groundwater recharge also encompasses water moving away from the water table farther into the saturated zone. Recharge occurs both naturally and through anthropogenic processes, where rainwater and/or reclaimed water is routed to the subsurface.

<span class="mw-page-title-main">Overdrafting</span> Unsustainable extraction of groundwater

Overdrafting is the process of extracting groundwater beyond the equilibrium yield of an aquifer. Groundwater is one of the largest sources of fresh water and is found underground. The primary cause of groundwater depletion is the excessive pumping of groundwater up from underground aquifers. Insufficient recharge can lead to depletion, reducing the usefulness of the aquifer for humans. Depletion can also have impacts on the environment around the aquifer, such as soil compression and land subsidence, local climatic change, soil chemistry changes, and other deterioration of the local environment.

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">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. 279. The Geological Society of London: 1–3. doi:10.1144/sp279.1. S2CID   130950517 . Retrieved 29 September 2022.
  9. Forgrave, Andrew. "Rescuers plea to cavers using 'extremely cold' underground Snowdonia lake". North Wales Live. The Daily Post. Retrieved 12 April 2024.
  10. "Discover and Experience". Salz Welten. Retrieved 2 October 2022.

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