Editing Cave (section)

==Formation types==
The formation and development of caves is known as ''[[speleogenesis]]''; it can occur over the course of millions of years.<ref name=":0">{{Cite journal|last1=Laureano|first1=Fernando V.|last2=Karmann|first2=Ivo|last3=Granger|first3=Darryl E.|last4=Auler|first4=Augusto S.|last5=Almeida|first5=Renato P.|last6=Cruz|first6=Francisco W.|last7=Strícks|first7=Nicolás M.|last8=Novello|first8=Valdir F.|date=2016-11-15|title=Two million years of river and cave aggradation in NE Brazil: Implications for speleogenesis and landscape evolution|journal=Geomorphology|volume=273|pages=63–77|doi=10.1016/j.geomorph.2016.08.009|bibcode=2016Geomo.273...63L}}</ref> Caves can range widely in size, and are formed by various geological processes. These may involve a combination of chemical processes, erosion by water, tectonic forces, microorganisms, pressure, and atmospheric influences. Isotopic dating techniques can be applied to cave sediments, to determine the timescale of the geological events which formed and shaped present-day caves.<ref name=":0" />

It is estimated that a cave cannot be more than {{convert|3000|m}} vertically beneath the surface due to the pressure of overlying rocks. This does not, however, impose a maximum depth for a cave which is measured from its highest entrance to its lowest point, as the amount of rock above the lowest point is dependent on the topography of the landscape above it. For [[karst]] caves the maximum depth is determined on the basis of the lower limit of karst forming processes, coinciding with the base of the soluble carbonate rocks.<ref>[http://www.rgo-speleo.ru/books/termin/termin1.htm#a9 Комиссия спелеологии и карстоведения. Д. А. Тимофеев, В. Н. Дублянский, Т. З. Кикнадзе. Терминология карста. Базис карстования] {{Webarchive|url=https://web.archive.org/web/20130215034652/http://www.rgo-speleo.ru/books/termin/termin1.htm#a9 |date=2013-02-15 }} D.A. Timofeev, V.N. Dublyansky, T.Z. Kiknadze, 1991, ''Karst Terminology'', The Commission for Speleology and Karst, Moscow Center of the Russian Geographical Society<!-- Google translate --></ref> Most caves are formed in [[limestone]] by [[Solvation|dissolution]].<ref>{{cite web|url=https://www.pbs.org/wgbh/nova/earth/how-caves-form.html|publisher=[[Nova (American TV series)]]|title=How Caves Form|access-date=2013-07-01}}</ref>

Caves can be classified in various other ways as well, including a contrast between active and relict: active caves have water flowing through them; relict caves do not, though water may be retained in them. Types of active caves include inflow caves ("into which a stream sinks"), outflow caves ("from which a stream emerges"), and through caves ("traversed by a stream").<ref>{{Cite book |url=https://books.google.com/books?id=NsscjizazXAC&pg=PA38 |title=The Cave Book|last=Silvestru|first=Emil |date=2008|publisher=New Leaf|isbn=9780890514962|page=38}}</ref>
[[File:HallOfTheMountainKings.jpg|thumb|[[Speleothem]]s in Hall of the Mountain King of [[Ogof Craig a Ffynnon]], a solutional cave in [[South Wales]].]]

===Solutional===
{{Main|Solutional cave}}
'''Solutional caves''' or '''karst caves''' are the most frequently occurring caves. Such caves form in rock that is soluble; most occur in [[limestone]], but they can also form in other rocks including [[chalk]], [[Dolomite (rock)|dolomite]], [[marble]], salt, and [[gypsum]]. Except for [[Salt_cave|salt caves]], solutional caves result when rock is dissolved by natural acid in [[groundwater]] that seeps through [[bedding planes]], [[Fault (geology)|faults]], joints, and comparable features. Over time cracks enlarge to become caves and cave systems.

The largest and most abundant solutional caves are located in limestone. Limestone dissolves under the action of rainwater and groundwater charged with H<sub>2</sub>CO<sub>3</sub> ([[carbonic acid]]) and naturally occurring [[organic acid]]s. The dissolution process produces a distinctive landform known as ''[[karst]]'', characterized by [[sinkhole]]s and underground drainage. Limestone caves are often adorned with [[calcium carbonate]] formations produced through slow [[Precipitation (chemistry)|precipitation]]. These include [[flowstone]]s, [[stalactite]]s, [[stalagmite]]s, [[helictite]]s, [[soda straw]]s and columns. These secondary mineral deposits in caves are called ''[[speleothem]]s''.

The portions of a solutional cave that are below the [[water table]] or the local level of the groundwater will be flooded.<ref>{{cite web |url=http://www.amazingcaves.com/learn_formed.html |title=Learning about caves; how caves are formed |access-date=September 8, 2009 |author=John Burcham |work=Journey into amazing caves |publisher=Project Underground |url-status=dead |archive-url=https://web.archive.org/web/20090503192150/http://www.amazingcaves.com/learn_formed.html |archive-date=May 3, 2009 }}</ref>

[[Lechuguilla Cave]] in [[New Mexico]] and nearby [[Carlsbad Cavern]] are now believed to be examples of another type of solutional cave. They were formed by H<sub>2</sub>S ([[hydrogen sulfide]]) gas rising from below, where reservoirs of oil give off sulfurous fumes. This gas mixes with groundwater and forms H<sub>2</sub>SO<sub>4</sub> ([[sulfuric acid]]). The acid then dissolves the limestone from below, rather than from above, by acidic water percolating from the surface.

===Primary===
<!--{{main|Primary cave}}-->
[[File:hawaiian lava tube.jpg|thumb|Exploring a [[lava tube]] in [[Hawaii]].]]
Caves formed at the same time as the surrounding rock are called '''primary caves'''.

[[Lava tube]]s are formed through [[volcanic]] activity and are the most common primary caves. As [[lava]] flows downhill, its surface cools and solidifies. Hot liquid lava continues to flow under that crust, and if most of it flows out, a hollow tube remains. Such caves can be found in the [[Canary Islands]], [[Jeju Province|Jeju-do]], the basaltic plains of [[Eastern Idaho]], and in other places. [[Kazumura Cave]] near [[Hilo]], [[Hawaii (island)|Hawaii]] is a remarkably long and deep lava tube; it is {{convert|65.6|km|mi|abbr=on|adj=mid|long}}.

Lava caves include but are not limited to lava tubes. Other caves formed through volcanic activity include rifts, lava molds, open vertical conduits, inflationary, blisters, among others.<ref name="ENCYCLO">{{cite book|page=84|title=Encyclopedia of Caves|first=David C.|last=Culver|publisher=Elsevier Academic Press|year=2004|isbn=978-0121986513}}</ref>

===Sea or littoral===
{{Main|Sea cave}}
[[File:Painted cave.jpg|thumb|Painted Cave, a large [[sea cave]], [[Santa Cruz Island]], [[California]]]]
Sea caves are found along coasts around the world. A special case is littoral caves, which are formed by wave action in zones of weakness in sea cliffs. Often these weaknesses are faults, but they may also be dykes or bedding-plane contacts. Some wave-cut caves are now above sea level because of later uplift. Elsewhere, in places such as [[Thailand]]'s [[Phang Nga Bay]], solutional caves have been flooded by the sea and are now subject to littoral erosion. Sea caves are generally around {{convert|5|to|50|m}} in length, but may exceed {{convert|300|m}}.

===Erosional===
[[Image:Sodom Salt Cave 031712.JPG|thumb|[[Halite|Salt]] cave in [[Mount Sodom]]]]
Erosional caves are those that form entirely by erosion by flowing streams carrying rocks and other sediments. These can form in any type of rock, including hard rocks such as granite. Generally there must be some zone of weakness to guide the water, such as a fault or joint. A subtype of the erosional cave is the wind or aeolian cave, carved by wind-born sediments.<ref name="ENCYCLO"/> Many caves formed initially by solutional processes often undergo a subsequent phase of erosional or vadose enlargement where active streams or rivers pass through them.<ref>{{Cite web |title=Erosional Caves |url=https://caves.org/erosional-caves/ |access-date=2025-02-12 |website=National Speleological Society |language=en-US}}</ref>

===Glacier===
{{Main|Glacier cave}}
[[File:Big Four Glacier Ice cave.jpg|thumb|[[Glacier cave]] in Big Four Glacier, [[Big Four Mountain]], [[Washington (state)|Washington]], {{circa}} 1920]]
Glacier caves are formed by melting ice and flowing water within and under glaciers. The cavities are influenced by the [[Creep (deformation)|very slow flow]] of the ice, which tends to collapse the caves again. Glacier caves are sometimes misidentified as "[[ice cave]]s", though this latter term is properly reserved for bedrock caves that contain year-round ice formations.

===Fracture===
Fracture caves are formed when layers of more soluble minerals, such as gypsum, dissolve out from between layers of less soluble rock. These rocks fracture and collapse in blocks of stone.<ref>{{Cite journal|last1=Mörner|first1=Nils-Axel|last2=Sjöberg|first2=Rabbe|date=September 2018|title=Merging the concepts of pseudokarst and paleoseismicity in Sweden: A unified theory on the formation of fractures, fracture caves, and angular block heape|journal=International Journal of Speleology|volume=47|issue=3|pages=393–405|doi=10.5038/1827-806X.47.3.2225|issn=0392-6672|doi-access=free}}</ref>

===Talus<span class="anchor" id="Talus_cave"></span>===
{{Main|Talus cave}}
Talus caves are formed by the openings among large boulders that have fallen down into a random heap, often at the bases of cliffs.<ref>{{Cite journal|last1=Kolawole|first1=F.|last2=Anifowose|first2=A. Y. B.|date=2011-01-01|title=Talus Caves: Geotourist Attractions Formed by Spheroidal and Exfoliation Weathering on Akure-Ado Inselbergs, Southwestern Nigeria.|journal=Ethiopian Journal of Environmental Studies and Management|volume=4|issue=3|pages=1–6|doi=10.4314/ejesm.v4i3.1|issn=1998-0507|doi-access=free}}</ref> These unstable deposits are called talus or [[scree]], and may be subject to frequent [[rockfall]]s and [[landslide]]s.

===Anchialine===
{{Main|Anchialine cave}}
Anchialine caves are caves, usually coastal, containing a mixture of freshwater and saline water (usually sea water). They occur in many parts of the world, and often contain highly specialized and endemic fauna.<ref>{{Cite web|title=Peldanga Labyrinth (Liepniekvalka Caves), Latvia - redzet.eu|url=https://www.redzet.eu/en/photo/peldanga-labyrinth-liepniekvalka-caves-latvia-A-261-15|website=www.redzet.eu|access-date=2020-05-17}}</ref>