Editing Karst (section)

== Development ==
[[File:Limestone Eocene deposit at Sinj Stari grad - Dalmatia - Croatia IMG 20210820 083857.jpg|thumb|A limestone deposit in the [[Dinaric Alps]] near [[Sinj|Sinj, Croatia]]]]
Karst is most strongly developed in dense [[carbonate rock]], such as limestone, that is thinly [[Bed (geology)|bedded]] and highly [[Joint (geology)|fractured]]. Karst is not typically well developed in [[chalk]], 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 with [[Entrenched river|entrenched 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.<ref name="thornbury-1969">{{cite book |last1=Thornbury |first1=William D. |title=Principles of geomorphology |date=1969 |publisher=Wiley |location=New York |isbn=0471861979 |pages=303–344 |edition=2d}}</ref><ref>{{cite web |title=Karst Landscapes of Illinois: Dissolving Bedrock and Collapsing Soil |url=https://isgs.illinois.edu/outreach/geology-resources/karst-landscapes-illinois-dissolving-bedrock-and-collapsing-soil |website=Prairie Research Institute |publisher=Illinois State Geological Survey |access-date=26 December 2020 |archive-date=2 December 2020 |archive-url=https://web.archive.org/web/20201202003934/https://isgs.illinois.edu/outreach/geology-resources/karst-landscapes-illinois-dissolving-bedrock-and-collapsing-soil |url-status=dead }}</ref>

===Chemistry of dissolution===
The [[carbonic acid]] that causes karst features is formed as rain passes through [[Earth's atmosphere]] picking up [[carbon dioxide]] ({{CO2}}), which readily dissolves in the water. Once the rain reaches the ground, it may pass through [[soil]] that provides additional {{CO2}} produced by [[soil respiration]]. Some of the dissolved carbon dioxide reacts with the water to form a weak carbonic acid solution, which dissolves [[calcium carbonate]].<ref>{{cite web |last1=Grove |first1=Glenn E. |title=Karst Features and the Dissolution of Carbonate Rocks in Crawford County |url=https://www.in.gov/dnr/water/files/crawford_text_karst.pdf |publisher=Indiana Department of Natural Resources, Division of Water, Resource Assessment Section |access-date=26 December 2020 |date=September 2003}}</ref> The primary reaction sequence in limestone dissolution is the following:<ref>{{cite encyclopedia |last1=Wolfgang |first1=Dreybrodt |year=2004 |title=Dissolution: Carbonate rocks |encyclopedia=Encyclopedia of Caves and Karst Science |pages=295–298 |url=https://www.researchgate.net/publication/313171146 |access-date=26 December 2020}}</ref>
[[File:Kostivere karst area.jpg|thumb|Kostivere karst area in Estonia]]
:{{chem2|H2O + CO2 -> H2CO3}}
:{{chem2|CaCO3 + H2CO3 -> Ca(2+) + 2 HCO3−}}

In very rare conditions, oxidation can play a role. Oxidation played a major role in the formation of ancient [[Lechuguilla Cave]] in the US state of [[New Mexico]]<ref>{{cite journal |last1=Davis |first1=D.G. |year=2000 |title=Extraordinary features of Lechuguilla Cave, Guadalupe Mountains, New Mexico |journal=Journal of Cave and Karst Studies |volume=62 |number=2 |pages=147–157 |citeseerx=10.1.1.521.9303 }}</ref> and is presently active in the [[Frasassi Caves]] of Italy.<ref>{{cite journal |last1=Galdenzi |first1=S. |last2=Maruoka |first2=T. |year=2003 |title=Gypsum deposits in the Frasassi Caves, central Italy |journal=Journal of Cave and Karst Studies |volume=65 |number=2 |pages=111–125 |url=https://www.researchgate.net/publication/279620470 |access-date=24 February 2021}}</ref> 
[[File:karst Dent-de-Crolle-8.jpg|right|thumb|[[Limestone pavement]] on [[Dent de Crolles|Dent de Crolles, France]]]]
The oxidation of [[sulfide]]s leading to the formation of [[sulfuric acid]] can also be one of the corrosion factors in karst formation. As [[oxygen]]-rich surface waters seep into deep anoxic karst systems, they bring oxygen, which reacts with sulfide present in the system ([[pyrite]] or [[hydrogen sulfide]]) to form sulfuric acid ({{chem2|H2SO4}}). Sulfuric acid then reacts with calcium carbonate, causing increased erosion within the limestone formation. This [[Chain reaction|chain of reaction]]s is:
:{{chem2|H2S + 2 O2 -> H2SO4}} (sulfide oxidation)
:{{chem2|H2SO4 + 2 H2O -> SO4(2-) + 2 H3O+}} (sulfuric acid dissociation)
:{{chem2|CaCO3 + 2 H3O+ -> Ca(2+) + H2CO3 + 2 H2O}} (calcium carbonate dissolution)
:{{chem2|Ca(2+) + SO4(2-) -> CaSO4}} (formation of calcium sulfate)
:{{chem2|CaSO4 + 2 H2O -> [CaSO4*2H2O]}} (formation of gypsum)

This reaction chain forms [[gypsum]].<ref>{{cite journal |year=2008 |first1=S. |last1=Galdenzi |first2=M. |last2=Cocchioni |first3=L. |last3=Morichetti |first4=V. |last4=Amici |first5=S. |last5=Scuri |display-authors=3|title=Sulfidic ground water chemistry in the Frasassi Cave, Italy |journal=Journal of Cave and Karst Studies |volume=70 |issue=2 |pages=94–107 |url=http://wvvw.caves.org/pub/journal/PDF/v70/cave-70-02-94.pdf |access-date=2012-11-29 |archive-date=2016-03-04 |archive-url=https://web.archive.org/web/20160304044009/http://wvvw.caves.org/pub/journal/PDF/v70/cave-70-02-94.pdf |url-status=dead }}</ref>