Editing Karst (section)

== Hydrology ==
[[File:KarstterrainUSGS.jpg|thumb|upright=2|alt=Cross section of karst terrain showing topographic features and water flow paths.|Features typical of well-developed karst terrain]]
[[File: Puerto Princesa Underground River.jpg|thumb|The [[Puerto-Princesa Subterranean River National Park|Puerto Princesa Underground River]], Philippines]]

Karst formations have unique hydrology, resulting in many unusual features. A [[karst fenster]] (karst window) occurs when an underground stream emerges onto the surface between layers of rock, [[waterfall#Types of waterfalls|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, like [[Ljubljanica]], the "river of seven names".

Another example of this is the [[Popo Agie Wilderness|Popo Agie River]] in [[Fremont County, Wyoming]], where, at a site named "The Sinks" in [[Sinks Canyon State Park]], the river flows into a cave in a formation known as the Madison Limestone and then rises again {{convert|1/2|mi|m|order=flip|abbr=on}} down the canyon in a placid pool.

A [[Turlough (lake)|turlough]] 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.

=== Aquifers ===
{{Main|Aquifer#Karst}}
[[File:MammothCaveNPS.jpg|thumb|left |alt=Several people in a jon boat on a river inside a cave. |Water in karst aquifers flows through open conduits where water flows as underground streams.]]
[[Karst]] aquifers typically develop in [[limestone]]. Surface water containing natural [[carbonic 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.<ref>{{cite book |last=Dreybrodt |first=Wolfgang |date=1988 |title=Processes in karst systems: physics, chemistry, and geology |volume=4 |location=Berlin |publisher=Springer |pages=2–3 |isbn=978-3-642-83354-0 |doi=10.1007/978-3-642-83352-6 |series=Springer Series in Physical Environment }}</ref>

Characterization of karst aquifers requires field exploration to locate [[sinkhole|sinkholes, swallets]], [[Losing stream|sinking streams]], and [[Spring (hydrology)|springs]] in addition to studying [[geological map]]s.<ref name="DelineationGrdwtrBasinsTaylor">{{cite book |last=Taylor |first=Charles |date=1997 |title=Delineation of ground-water basins and recharge areas for municipal water-supply springs in a karst aquifer system in the Elizabethtown area, Northern Kentucky |url=https://pubs.usgs.gov/wri/1996/4254/report.pdf |location=Denver, Colorado |publisher=U.S. Geological Survey |series=Water-Resources Investigations Report 96-4254 |doi=10.3133/wri964254 }}</ref>{{rp|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 with [[Dye tracing|dye traces]], measurement of spring discharges, and analysis of water chemistry.<ref>{{cite book |last1=Taylor |first1=Charles |last2=Greene |first2=Earl |date=2008 |title=Field Techniques for Estimating Water Fluxes Between Surface Water and Ground Water |chapter=Hydrogeologic characterization and methods used in the investigation of karst hydrology. |chapter-url=https://pubs.usgs.gov/tm/04d02/pdf/TM4-D2-chap3.pdf |archive-url=https://web.archive.org/web/20081102202902/http://pubs.usgs.gov/tm/04d02/pdf/TM4-D2-chap3.pdf |archive-date=2008-11-02 |url-status=live |series=Techniques and Methods 4–D2 |publisher=U.S. Geological Survey |page=107 }}</ref> 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.<ref>{{cite journal |last1=Renken |first1=R. |last2=Cunningham |first2=K. |last3=Zygnerski |first3=M. |last4=Wacker |first4=M. |last5=Shapiro |first5=A. |last6=Harvey |first6=R. |last7=Metge |first7=D. |last8=Osborn |first8=C. |last9=Ryan |first9=J. |date=November 2005 |title=Assessing the Vulnerability of a Municipal Well Field to Contamination in a Karst Aquifer |journal= Environmental and Engineering Geoscience |publisher=GeoScienceWorld|volume=11 |number=4 |page=320 |doi=10.2113/11.4.319 |bibcode=2005EEGeo..11..319R |citeseerx=10.1.1.372.1559 }}</ref>
[[File:Source de la Loue3.JPG|thumb|A [[karst spring]] in the [[Jura Mountains]] near [[Ouhans]] in eastern France at the source of the river [[Loue]]]]

Linear alignment of surface features such as straight stream segments and sinkholes develop along [[Fracture (geology)|fracture traces]]. Locating a well in a fracture trace or intersection of fracture traces increases the likelihood to encounter good water production.<ref>{{cite book |last=Fetter |first=Charles |date=1988 |title=Applied Hydrology |location=Columbus, Ohio |publisher=Merrill |pages=294–295 |isbn=978-0-675-20887-1 }}</ref> Voids in karst aquifers can be large enough to cause destructive collapse or [[subsidence]] of the ground surface that can initiate a catastrophic release of contaminants.<ref name="FieldMethodsGeoHydrogeo">{{cite book|last1= Assaad |first1= Fakhry |last2=LaMoreaux |first2=Philip |last3=Hughes |first3=Travis |date=2004 |title=Field methods for geologists and hydrogeologists |location=Berlin, Germany |publisher= Springer-Verlag Berlin Heidelberg |isbn= 978-3-540-40882-6 |doi=10.1007/978-3-662-05438-3}}</ref>{{rp|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&nbsp;km/d).<ref>{{cite journal |last1=Scanlon |first1=Bridget|author1-link= Bridget Scanlon |last2=Mace |first2=Robert |last3=Barrett |first3=Michael |last4=Smith |first4=Brian |date=2003  |title= Can we simulate regional groundwater flow in a karst system using equivalent porous media models? Case study, Barton Springs Edwards aquifer, USA |journal= Journal of Hydrology |publisher=Elsevier Science |volume=276 |issue= 1–4|page=142 |doi= 10.1016/S0022-1694(03)00064-7 |bibcode=2003JHyd..276..137S|s2cid=16046040 }}</ref> The rapid groundwater flow rates make karst aquifers much more sensitive to groundwater contamination than porous aquifers.<ref name="DelineationGrdwtrBasinsTaylor" />{{rp|1}}

[[Groundwater]] in karst areas is also just as easily [[Water pollution|polluted]] as surface streams, because Karst formations are cavernous and highly permeable, resulting in reduced opportunity for contaminant filtration.

[[Water well|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 a [[Aquifer#Porous versus karst|porous aquifer]]. Sinkholes have often been used as farmstead or community [[landfill|trash dumps]]. Overloaded or malfunctioning [[septic tank]]s 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|lc=y}}, supplied about 25% of the global demand for drinkable water.<ref>{{cite journal |last1=Parise |first1=M. |last2=Gunn |first2=J. |title=Natural and anthropogenic hazards in karst areas: an introduction |url=https://sp.lyellcollection.org/content/279/1/1 |journal=Geological Society, London, Special Publications |access-date=9 October 2021 |pages=1–3 |language=en |doi=10.1144/SP279.1 |date=1 January 2007|volume=279 |issue=1 |bibcode=2007GSLSP.279....1P |s2cid=130950517 }}</ref>

=== Effects of karst hydrology ===
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 progressive [[erosion]] 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 the [[National Corvette Museum]] in [[Bowling Green, Kentucky]] in 2014.<ref>{{Cite web|url=https://www.cnn.com/2014/02/13/travel/corvette-museum-sinkhole/index.html|title=Mood somber, repairs uncertain as Corvette museum opens|last=Patterson|first=Thom|website=CNN|date=13 February 2014|access-date=2019-08-26}}</ref>