Subterranean drainage may limit surface water, with few to no rivers or lakes. In regions where the dissolvedbedrock is covered (perhaps by debris) or confined by one or more superimposed non-soluble rock strata, distinctive karst features may occur only at subsurface levels and can be totally missing above ground.[4]
Global distribution of major outcrops of carbonate rocks (mainlylimestone, exceptevaporites)
The English wordkarst was borrowed fromGermanKarst in the late 19th century,[6] which entered German usage much earlier,[7] to describe a number of geological, geomorphological, and hydrological features found within therange of theDinaric Alps, stretching from the northeastern corner ofItaly above the city ofTrieste, across theBalkan peninsula along the coast of the easternAdriatic toKosovo andNorth Macedonia, where themassif of theŠar Mountains begins. The karst zone is at the northwesternmost section, described in early topographical research as aplateau between Italy andSlovenia. Languages preserving this form includeItalian:Carso,German:Karst, andAlbanian:karsti.
In the localSouth Slavic languages, all variations of the word are derived from a RomanizedIllyrian base (yieldingLatin:carsus,Dalmatian:carsus), latermetathesized from the reconstructed form*korsъ into forms such asSlovene:kras[8] andSerbo-Croatian:krš,kras,[9][10][11][12] first attested in the 18th century, and the adjective formkraški in the 16th century.[13] As a proper noun, the Slovene formGrast was first attested in 1177.[14]
Ultimately, the word is ofMediterranean origin. It has also been suggested that the word may derive from theProto-Indo-European rootkarra- 'rock'.[15] The name may also be connected to theoronymKar(u)sádios oros cited byPtolemy, and perhaps also to LatinCarusardius.[13][14]
Jovan Cvijić greatly advanced the knowledge of karst regions to the point where he became known as the "father of karst geomorphology". Primarily discussing the karst regions of the Balkans, Cvijić's 1893 publicationDas Karstphänomen describes landforms such as karren,dolines andpoljes.[5] In a 1918 publication, Cvijić proposed acyclical model for karst landscape development.[5][17]
Karsthydrology emerged as a discipline in the late 1950s and the early 1960s in France. Previously, the activities of cave explorers, calledspeleologists, had been dismissed as more of a sport than a science and so the undergroundkarst caves and their associated watercourses were, from a scientific perspective, understudied.[18]
Karst is most strongly developed in densecarbonate rock, such as limestone, that is thinlybedded and highlyfractured. Karst is not typically well developed inchalk, because chalk is highly porous rather than dense, so the flow of groundwater is not concentrated along fractures. Karst is also most strongly developed where the water table is relatively low, such as in uplands withentrenched valleys, and where rainfall is moderate to heavy. This contributes to rapid downward movement of groundwater, which promotes dissolution of the bedrock, whereas standing groundwater becomes saturated with carbonate minerals and ceases to dissolve the bedrock.[19][20]
Thecarbonic acid that causes karst features is formed as rain passes throughEarth's atmosphere picking upcarbon dioxide (CO2), which readily dissolves in the water. Once the rain reaches the ground, it may pass throughsoil that provides additional CO2 produced bysoil respiration. Some of the dissolved carbon dioxide reacts with the water to form a weak carbonic acid solution, which dissolvescalcium carbonate.[21] The primary reaction sequence in limestone dissolution is the following:[22]
Kostivere karst area in Estonia
H2O
+
CO2
→
H2CO3
CaCO3
+
H2CO3
→
Ca2+
+
2HCO− 3
In very rare conditions, oxidation can play a role. Oxidation played a major role in the formation of ancientLechuguilla Cave in the US state ofNew Mexico[23] and is presently active in theFrasassi Caves of Italy.[24]
The oxidation ofsulfides leading to the formation ofsulfuric acid can also be one of the corrosion factors in karst formation. Asoxygen (O2)-rich surface waters seep into deep anoxic karst systems, they bring oxygen, which reacts with sulfide present in the system (pyrite orhydrogen sulfide) to form sulfuric acid (H2SO4). Sulfuric acid then reacts with calcium carbonate, causing increased erosion within the limestone formation. Thischain of reactions is:
The karstification of a landscape may result in a variety of large- or small-scale features both on the surface and beneath. On exposed surfaces, small features may includesolution flutes (or rillenkarren),runnels,limestone pavement (clints and grikes),kamenitzas collectively called karren or lapiez. Medium-sized surface features may includesinkholes orcenotes (closed basins), vertical shafts,foibe (inverted funnel shaped sinkholes), disappearing streams, and reappearingsprings.
Large-scale features may includelimestone pavements,poljes, and karst valleys. Mature karst landscapes, where more bedrock has been removed than remains, may result inkarst towers, orhaystack/eggbox landscapes. Beneath the surface, complex underground drainage systems (such as karstaquifers) and extensivecaves and cavern systems may form.[19]
Erosion along limestone shores, notably in thetropics, produces karst topography that includes a sharp makatea surface above the normal reach of the sea, and undercuts that are mostly the result of biological activity orbioerosion at or a little abovemean sea level.[26] Some of the most dramatic of these formations can be seen inThailand'sPhangnga Bay and atHalong Bay inVietnam.
Calcium carbonate dissolved into water may precipitate out where the water discharges some of its dissolved carbon dioxide. Rivers which emerge from springs may producetufa terraces, consisting of layers of calcite deposited over extended periods of time. In caves, a variety of features collectively calledspeleothems are formed by deposition of calcium carbonate and other dissolved minerals.
Kegelkarst is a type of tropical karst terrain with numerous cone-like hills, formed by cockpits,mogotes, andpoljes and without strong fluvial erosion processes. This terrain is found in Cuba, Jamaica, Indonesia, Malaysia, the Philippines, Puerto Rico, southern China, Myanmar, Thailand, Laos and Vietnam.[28]
Salt karst (or 'halite karst') is developed in areas wheresalt is undergoing solution underground. It can lead to surface depressions and collapses which present a geo-hazard.[29]
Karst areas tend to have unique types of forests. The karst terrain is difficult for humans to traverse, so that their ecosystems are often relatively undisturbed. The soil tends to have a high pH, which encourages growth of unusual species of orchids, palms, mangroves, and other plants.[30]
Paleokarst or palaeokarst is a development of karst observed in geological history and preserved within the rock sequence, effectively a fossil karst. There are for example palaeokarst surfaces exposed within the Clydach Valley Subgroup of theCarboniferous Limestone sequence ofSouth Wales which developed as sub-aerialweathering of recently formed limestones took place during periods of non-deposition within the early part of the period. Sedimentation resumed and further limestone strata were deposited on an irregular karst surface, the cycle recurring several times in connection with fluctuating sea levels over prolonged periods.[31]
Pseudokarsts are similar in form or appearance to karst features but are created by different mechanisms. Examples includelava caves andgranitetors—for example, Labertouche Cave inVictoria, Australia—andpaleocollapse features.Mud Caves are an example of pseudokarst.
Karst formations have unique hydrology, resulting in many unusual features. Akarst fenster (karst window) occurs when an underground stream emerges onto the surface between layers of rock,cascades some distance, and then disappears back down, often into a sinkhole.
Rivers in karst areas may disappear underground a number of times and spring up again in different places, even under a different name, likeLjubljanica, the "river of seven names".
Another example of this is thePopo Agie River inFremont County, Wyoming, where, at a site named "The Sinks" inSinks Canyon State Park, the river flows into a cave in a formation known as the Madison Limestone and then rises again 800 m (1⁄2 mi) down the canyon in a placid pool.
Aturlough is a unique type of seasonal lake found in Irish karst areas which are formed through the annual welling-up of water from the underground water system.
Water in karst aquifers flows through open conduits where water flows as underground streams.
Karst aquifers typically develop inlimestone. Surface water containing naturalcarbonic acid moves down into small fissures in limestone. This carbonic acid gradually dissolves limestone thereby enlarging the fissures. The enlarged fissures allow a larger quantity of water to enter which leads to a progressive enlargement of openings. Abundant small openings store a large quantity of water. The larger openings form a conduit system that drains the aquifer to springs.[32]
Characterization of karst aquifers requires field exploration to locatesinkholes, swallets,sinking streams, andsprings in addition to studyinggeologic maps.[33]: 4 Conventional hydrogeologic methods such as aquifer tests and potentiometric mapping are insufficient to characterize the complexity of karst aquifers, and need to be supplemented withdye traces, measurement of spring discharges, and analysis of water chemistry.[34] U.S. Geological Survey dye tracing has determined that conventional groundwater models that assume a uniform distribution of porosity are not applicable for karst aquifers.[35]
Linear alignment of surface features such as straight stream segments and sinkholes develop alongfracture traces. Locating a well in a fracture trace or intersection of fracture traces increases the likelihood to encounter good water production.[36] Voids in karst aquifers can be large enough to cause destructive collapse orsubsidence of the ground surface that can initiate a catastrophic release of contaminants.[37]: 3–4
Groundwater flow rate in karst aquifers is much more rapid than in porous aquifers. For example, in the Barton Springs Edwards aquifer, dye traces measured the karst groundwater flow rates from 0.5 to 7 miles per day (0.8 to 11.3 km/d).[38] The rapid groundwater flow rates make karst aquifers much more sensitive to groundwater contamination than porous aquifers.[33]: 1
Groundwater in karst areas is also just as easilypolluted as surface streams, because Karst formations are cavernous and highly permeable, resulting in reduced opportunity for contaminant filtration.
Well water may also be unsafe as the water may have run unimpeded from a sinkhole in a cattle pasture, bypassing the normal filtering that occurs in aporous aquifer. Sinkholes have often been used as farmstead or communitytrash dumps. Overloaded or malfunctioningseptic tanks in karst landscapes may dump raw sewage directly into underground channels.
Geologists are concerned with these negative effects of human activity on karst hydrology which, as of 2007[update], supplied about 25% of the global demand for drinkable water.[39]
Farming in karst areas must take into account the lack of surface water. The soils may be fertile enough, and rainfall may be adequate, but rainwater quickly moves through the crevices into the ground, sometimes leaving the surface soil parched between rains.
The karst topography also poses peculiar difficulties for human inhabitants. Sinkholes can develop gradually as surface openings enlarge, but progressiveerosion is frequently unseen until the roof of a cavern suddenly collapses. Such events have swallowed homes, cattle, cars, and farm machinery. In the United States, sudden collapse of such a cavern-sinkhole swallowed part of the collection of theNational Corvette Museum inBowling Green, Kentucky in 2014.[40]
Lunan Stone Forest, Yunnan, ChinaDrone video of Kostivere karst area in Estonia (2021)
The world's largest limestone karst is Australia'sNullarbor Plain. Slovenia has the world's highest risk of sinkholes, while the westernHighland Rim in the eastern United States is at the second-highest risk of karst sinkholes.[41][42]
Many karst-related terms derive fromSouth Slavic languages, entering scientific vocabulary through early research in the Western Balkan Dinaric Alpine karst.
Abîme, a vertical shaft in karst that may be very deep and usually opens into a network of subterranean passages
Cenote, a deep sinkhole, characteristic of Mexico, resulting from collapse of limestone bedrock that exposes groundwater underneath
Doline, also sink or sinkhole, is a closed depression draining underground in karst areas. The name "doline" comes fromdolina, meaning "valley", and derives from South Slavic languages.
Karst window (also known as a "karst fenster"), a feature where a spring emerges briefly, with the water discharge then abruptly disappearing into a nearby sinkhole
Karst spring, a spring emerging from karst, originating a flow of water on the surface
Limestone pavement, a landform consisting of a flat, incised surface of exposed limestone that resembles an artificial pavement
The study of the various aspects of karst regions is called karst studies,[45] karst science,[46] or karstology.[47] This includes biological, chemical, ecological, geomorphological, hydrogeological, hydrological, political, socio-economical, and other processes over a variety of spatial and temporal scales in karst regions, with the purpose of understanding karst aquifers and ecosystems, and the development of the surface and underground structure, so that the environment can be protected and human activities planned effectively.[48] Prominent karst researchers includeJovan Cvijić andWilliam Morris Davis.
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^Jackson, Julia A., ed. (1997). "Karst".Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute.ISBN0922152349.
^Doerr, S. H. (18 March 1999). "Karst-like landforms and hydrology in quartzites of the Venezuelan Guyana shield: Pseudokarst or "real" karst?".Zeitschrift für Geomorphologie.43 (1):1–17.Bibcode:1999ZGm....43....1D.doi:10.1127/zfg/43/1999/1.
^Billi, Andrea; De Filippis, Luigi; Poncia, Pier Paolo; et al. (February 2016). "Hidden sinkholes and karst cavities in the travertine plateau of a highly-populated geothermal seismic territory (Tivoli, central Italy)".Geomorphology.255:63–80.Bibcode:2016Geomo.255...63B.doi:10.1016/j.geomorph.2015.12.011.
^abSnoj, Marko (2003).Slovenski etimološki slovar. Ljubljana: Modrijan. p. 318.
^abBezlaj, France (ed.). 1982.Etimološki slovar slovenskega jezika, vol. 2, K–O. Ljubljana: SAZU, p. 82.
^Gams, I.,Kras v Sloveniji — v prostoru in casu (Karst in Slovenia in space and time), 2003,ISBN961-6500-46-5.
^Paul Larsen,Scientific accounts of a vanishing lake: Janez Valvasor, Lake Cerknica and the New Philosophy, 2003.
^Cvijić, Jovan (1918). "Hydrographie souterraine et évolution morphologique du Karst".Recueil des travaux de l'institut de géographie alpine (in French).6 (4):375–426.doi:10.3406/rga.1918.4727.
^Gilli, Éric; Mangan, Christian; Mudry, Jacques (2012).Hydrogeology: Objectives, Methods, Applications. Translated by Fandel, Choél. CRC Press. p. 7.
^abThornbury, William D. (1969).Principles of geomorphology (2d ed.). New York: Wiley. pp. 303–344.ISBN0471861979.
^Wolfgang, Dreybrodt (2004)."Dissolution: Carbonate rocks".Encyclopedia of Caves and Karst Science. pp. 295–298. Retrieved26 December 2020.
^Davis, D.G. (2000). "Extraordinary features of Lechuguilla Cave, Guadalupe Mountains, New Mexico".Journal of Cave and Karst Studies.62 (2):147–157.CiteSeerX10.1.1.521.9303.
^Howells, M.F (2007).British Regional Geology:Wales. Keyworth, Nottingham: British Geological Survey. p. 118.ISBN978-085272584-9.
^Dreybrodt, Wolfgang (1988).Processes in karst systems: physics, chemistry, and geology. Springer Series in Physical Environment. Vol. 4. Berlin: Springer. pp. 2–3.doi:10.1007/978-3-642-83352-6.ISBN978-3-642-83354-0.
^Renken, R.; Cunningham, K.; Zygnerski, M.; Wacker, M.; Shapiro, A.; Harvey, R.; Metge, D.; Osborn, C.; Ryan, J. (November 2005). "Assessing the Vulnerability of a Municipal Well Field to Contamination in a Karst Aquifer".Environmental and Engineering Geoscience.11 (4). GeoScienceWorld: 320.Bibcode:2005EEGeo..11..319R.CiteSeerX10.1.1.372.1559.doi:10.2113/11.4.319.
^Fetter, Charles (1988).Applied Hydrology. Columbus, Ohio: Merrill. pp. 294–295.ISBN978-0-675-20887-1.
^Assaad, Fakhry; LaMoreaux, Philip; Hughes, Travis (2004).Field methods for geologists and hydrogeologists. Berlin, Germany: Springer-Verlag Berlin Heidelberg.doi:10.1007/978-3-662-05438-3.ISBN978-3-540-40882-6.
^Smith, D.G. (1987).Landforms of Alberta interpreted from airphotos and satellite imagery. Edmonton, Alberta: Alberta Remote Sensing Center. Alberta Environment. p. 81.ISBN0-919975-10-0.
Vermeulen, J.J., Whitten, T., "Biodiversity and Cultural Property in the Management of Limestone Resources in East Asia: Lessons from East Asia", The World Bank, 1999,ISBN978-0-821345-08-5
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