Sinkhole

File:Dead Sea sinkhole by David Shankbone.jpg, formed when underground salt is dissolved by freshwater intrusion, due to continuing sea-level drop.]]

File:Chinchón dolina c1991.jpg, Spain.]]

Sinkholes may capture surface drainage from running or standing water, but may also form in high and dry places in specific locations. Sinkholes that capture drainage can hold it in large limestone caves. These caves may drain into tributaries of larger rivers.{{Cite news|url=https://www.nytimes.com/2007/10/05/travel/escapes/05adventure.html|title=Getting Down and Dirty in an Underground River in Puerto Rico|last=Breining|first=Greg|date=5 October 2007|newspaper=The New York Times|issn=0362-4331|access-date=31 March 2016}}{{Cite journal|last=Palmer|first=Arthur N.|date=1 January 1991|title=Origin and morphology of limestone caves|journal=Geological Society of America Bulletin|language=en|volume=103|issue=1|pages=1–21|doi=10.1130/0016-7606(1991)103<0001:oamolc>2.3.co;2|bibcode=1991GSAB..103....1P|issn=0016-7606}}

The formation of sinkholes involves natural processes of erosion{{Cite book| last=Friend | first=Sandra | title=Sinkholes | publisher=Pineapple Press Inc | year=2002| isbn=978-1-56164-258-8 | page=[https://archive.org/details/sinkholes0000frie/page/11 11] | url=https://archive.org/details/sinkholes0000frie | url-access=registration | access-date = 7 June 2010}} or gradual removal of slightly soluble bedrock (such as limestone) by percolating water, the collapse of a cave roof, or a lowering of the water table.{{Sfn|Tills|2013|p=181}} Sinkholes often form through the process of suffosion.{{cite web |title=Quarrying and the environment |url=https://www.bgs.ac.uk/mendips/caveskarst/karst_3.htm |website=bgs |access-date=3 June 2018}} For example, groundwater may dissolve the carbonate cement holding the sandstone particles together and then carry away the lax particles, gradually forming a void.

Occasionally a sinkhole may exhibit a visible opening into a cave below. In the case of exceptionally large sinkholes, such as the Minyé sinkhole in Papua New Guinea or Cedar Sink at Mammoth Cave National Park in Kentucky, an underground stream or river may be visible across its bottom flowing from one side to the other.

Sinkholes are common where the rock below the land surface is limestone or other carbonate rock, salt beds, or in other soluble rocks, such as gypsum,{{cite web

|url = http://geology.utah.gov/surveynotes/geosights/sinkhole.htm

|title = Sinkholes in Washington County

|publisher = Utah gov Geological Survey

|url-status = dead

|archive-url = https://web.archive.org/web/20110323204811/http://www.geology.utah.gov/surveynotes/geosights/sinkhole.htm

|archive-date = 23 March 2011

|df = dmy-all

}} that can be dissolved naturally by circulating ground water. Sinkholes also occur in sandstone and quartzite terrains.

As the rock dissolves, spaces and caverns develop underground. These sinkholes can be dramatic, because the surface land usually stays intact until there is not enough support. Then, a sudden collapse of the land surface can occur.{{Sfn|Tills|2013|p=182}}

On 2 July 2015, scientists reported that active pits, related to sinkhole collapses and possibly associated with outbursts, were found on the comet 67P/Churyumov-Gerasimenko by the Rosetta space probe.{{cite journal|date=2 July 2015|title=Large heterogeneities in comet 67P as revealed by active pits from sinkhole collapse|journal=Nature|volume=523|issue=7558|pages=63–66|doi=10.1038/nature14564|author=Vincent, Jean-Baptiste|display-authors=etal|pmid=26135448|bibcode=2015Natur.523...63V|s2cid=2993705|url=https://hal-insu.archives-ouvertes.fr/insu-01176031/file/JBV2015.pdf }}{{cite news|url=http://apnews.excite.com/article/20150701/us-sci--comet_sinkholes-11254d29fb.html|title=It's the pits: Comet appears to have sinkholes, study says|last=Ritter|first=Malcolm|date=1 July 2015|work=AP News|access-date=2 July 2015}}

{{main|Pinge}}

File:Sinkhole.jpg in Atlanta, Georgia in 2005.]]

Collapses, commonly incorrectly labeled as sinkholes, also occur due to human activity, such as the collapse of abandoned mines and salt cavern storage in salt domes in places like Louisiana, Mississippi, and Texas, in the United States. More commonly, collapses occur in urban areas due to water main breaks or sewer collapses when old pipes give way. They can also occur from the overpumping and extraction of groundwater and subsurface fluids.

Sinkholes can also form when natural water drainage patterns are changed and new water diversion systems are developed. Some sinkholes form when the land surface is changed, such as when industrial and runoff storage ponds are created; the substantial weight of the new material can trigger a collapse of the roof of an existing void or cavity in the subsurface, resulting in development of a sinkhole.

Solution or dissolution sinkholes form where water dissolves limestone under a soil covering. Dissolution enlarges natural openings in the rock such as joints, fractures, and bedding planes. Soil settles down into the enlarged openings forming a small depression at the ground surface.{{cite web |url=https://www.usgs.gov/special-topic/water-science-school/science/sinkholes?qt-science_center_objects=0#qt-science_center_objects |title=Sinkholes |author= |website=Water Science School |publisher=U.S. Geological Survey |access-date=29 May 2019}}

File:Dissolution sinkhole.png

Cover-subsidence sinkholes form where voids in the underlying limestone allow more settling of the soil to create larger surface depressions.

File:Cover-subsidence sinkhole.png

Cover-collapse sinkholes or "dropouts" form where so much soil settles down into voids in the limestone that the ground surface collapses. The surface collapses may occur abruptly and cause catastrophic damages. New sinkhole collapses can also form when human activity changes the natural water-drainage patterns in karst areas.

File:Cover-collapse sinkhole.png

Pseudokarst sinkholes resemble karst sinkholes but are formed by processes other than the natural dissolution of rock.{{rp|4}}

File:Subsurface erosion of soil into karst conduit by water level fluctuation.jpg

The U.S. Geological Survey notes that "It is a frightening thought to imagine the ground below your feet or house suddenly collapsing and forming a big hole in the ground." Human activities can accelerate collapses of karst sinkholes, causing collapse within a few years that would normally evolve over thousands of years under natural conditions.{{cite book |last=Newton |first=John G. |date=1987 |chapter=Development of sinkholes resulting from man's activities in the eastern United States |series=U.S. Geological Survey Circular 968 |chapter-url=https://pubs.usgs.gov/circ/1987/0968/report.pdf |publisher=U.S. Government Print Office |doi=10.3133/cir968 |title=Circular |hdl=2027/uc1.31210020732440 }}{{rp|2}}{{cite book |last1=Kambesis |first1=P. |last2=Brucker |first2=R. |last3=Waltham |first3=T. |last4=Bell |first4=F. |last5= Culshaw |first5=M. |date=2005 |chapter= Collapse sinkhole at Dishman Lane, Kentucky |title=Sinkholes and Subsidence: Karst and Cavernous Rocks in Engineering and Construction |url=https://archive.org/details/sinkholessubside00walt |url-access=limited |location=Berlin |publisher= Springer |doi=10.1007/b138363 |page= [https://archive.org/details/sinkholessubside00walt/page/n303 281] |isbn=3-540-20725-2 }}{{cite book |last1=Benson |first1=Richard C. |last2=Yuhr |first2=Lynn B. |date=2015 |title= Site Characterization in Karst and Pseudokarst Terraines: Practical Strategies and Technology for Practicing Engineers, Hydrologists and Geologists |location= Dordrecht |publisher=Springer |doi= 10.1007/978-94-017-9924-9 |isbn= 978-94-017-9923-2 |s2cid=132318001 }}{{rp|1 and 92}} Soil-collapse sinkholes, which are characterized by the collapse of cavities in soil that have developed where soil falls down into underlying rock cavities, pose the most serious hazards to life and property. Fluctuation of the water level accelerates this collapse process. When water rises up through fissures in the rock, it reduces soil cohesion. Later, as the water level moves downward, the softened soil seeps downwards into rock cavities. Flowing water in karst conduits carries the soil away, preventing soil from accumulating in rock cavities and allowing the collapse process to continue.{{cite book |last=Sowers |first=George F. |date=1996 |title=Building on sinkholes |location=New York |publisher=American Society of Civil Engineers |doi=10.1061/9780784401767 |isbn=0-7844-0176-4 }}{{rp|52–53}}

Induced sinkholes occur where human activity alters how surface water recharges groundwater. Many human-induced sinkholes occur where natural diffused recharge is disturbed and surface water becomes concentrated. Activities that can accelerate sinkhole collapses include timber removal, ditching, laying pipelines, sewers, water lines, storm drains, and drilling. These activities can increase the downward movement of water beyond the natural rate of groundwater recharge.{{rp|26–29}} The increased runoff from the impervious surfaces of roads, roofs, and parking lots also accelerate man-induced sinkhole collapses.{{rp|8}}

Some induced sinkholes are preceded by warning signs, such as cracks, sagging, jammed doors, or cracking noises, but others develop with little or no warning.{{rp|32–34}} However, karst development is well understood, and proper site characterization can avoid karst disasters. Thus most sinkhole disasters are predictable and preventable rather than "acts of God".{{rp|xii}}{{rp|17 and 104}} The American Society of Civil Engineers has declared that the potential for sinkhole collapse must be a part of land-use planning in karst areas. Where sinkhole collapse of structures could cause loss of life, the public should be made aware of the risks.{{rp|88}}

The most likely locations for sinkhole collapse are areas where there is already a high density of existing sinkholes. Their presence shows that the subsurface contains a cave system or other unstable voids.{{Cite web|title=GIS and Spatial Statistical Methods for Determining Sinkhole Potential in Frederick Valley, Maryland, page 100 in Kuniansky, E.L., 2008, U.S. Geological Survey Karst Interest Group Proceedings, Bowling Green, Kentucky, May 27–29, 2008: U.S. Geological Survey Scientific Investigations Report 2008-5023, 142 p.|author-last= Doctor |author-first=Katarina|url =https://pubs.usgs.gov/sir/2008/5023/pdf/SIR2008-5023.pdf|publisher=U.S. Geological Survey |access-date = 27 November 2018}} Where large cavities exist in the limestone large surface collapses can occur, such the Winter Park, Florida sinkhole collapse.{{rp|91–92}} Recommendations for land uses in karst areas should avoid or minimize alterations of the land surface and natural drainage.{{rp|36}}

Since water level changes accelerate sinkhole collapse, measures must be taken to minimize water level changes. The areas most susceptible to sinkhole collapse can be identified and avoided.{{rp|88}} In karst areas the traditional foundation evaluations (bearing capacity and settlement) of the ability of soil to support a structure must be supplemented by geotechnical site investigation for cavities and defects in the underlying rock.{{rp|113}} Since the soil/rock surface in karst areas are very irregular the number of subsurface samples (borings and core samples) required per unit area is usually much greater than in non-karst areas.{{rp|98–99}}

File:December Giant sinkhole collapse USGS 1972.jpg, Alabama.]]

In 2015, the U.S. Geological Survey estimated the cost for repairs of damage arising from karst-related processes as at least $300 million per year over the preceding 15 years, but noted that this may be a gross underestimate based on inadequate data.{{cite book |url=http://pubs.er.usgs.gov/publication/70155910 |title=The cost of karst subsidence and sinkhole collapse in the United States compared with other natural hazards |last=Weary |first=David J.|editor1-first=Daniel |editor1-last=Doctor |editor2-first=Lewis |editor2-last=Land |editor3-first=J |editor3-last=Stephenson |date=2015 |website=USGS Publications Warehouse |publisher=University of South Florida |doi=10.5038/9780991000951 |isbn=978-0-9910009-5-1 |access-date=30 May 2019 }} The greatest amount of karst sinkhole damage in the United States occurs in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.{{cite journal |last1=Kuniansky |first1=E.L. |last2=Weary |first2=D.J. |last3=Kaufmann |first3=J.E. |date=2016 |title=The current status of mapping karst areas and availability of public sinkhole-risk resources in karst terrains of the United States |url=https://link.springer.com/content/pdf/10.1007%2Fs10040-015-1333-3.pdf |journal=Hydrogeology Journal |volume=24 |issue=3|page=614|publisher=Springer Berlin Heidelberg |doi=10.1007/s10040-015-1333-3 |access-date=5 May 2019 |bibcode=2016HydJ...24..613K |s2cid=130375566 |doi-access=free }} The largest recent sinkhole in the USA is possibly one that formed in 1972 in Montevallo, Alabama, as a result of man-made lowering of the water level in a nearby rock quarry. This "December Giant" or "Golly Hole" sinkhole measures {{convert|425|ft|m|order=flip|abbr=on|round=5}} long, {{convert|350|ft|m|order=flip|abbr=on|round=5}} wide and {{convert|150|ft|m|order=flip|abbr=on|round=5}} deep.{{rp|1–2}}{{rp|61–63}}{{cite web |url=https://library.usgs.gov/photo/#/item/51ddc5cae4b0f72b44720f4b |title=Possibly the nation's largest recent sinkhole – the 'December Giant' measuring 425 feet long, 350 feet wide and 150 feet deep – formed in central Alabama. |author= |website=USGS Denver Library Photographic Collection |publisher=U.S. Geological Survey |access-date=28 May 2019 }}

Other areas of significant karst hazards include the Ebro Basin in northern Spain; the island of Sardinia; the Italian peninsula; the Chalk areas in southern England; Sichuan, China; Jamaica; France;{{cite journal |last1=Parise |first1=M. |last2=Gunn |first2=J. |title=Natural and anthropogenic hazards in karst areas: an introduction |journal= Geological Society, London, Special Publications |date=2007 |volume=279 |issue=1 |pages=1–3 |doi=10.1144/SP279.1|bibcode=2007GSLSP.279....1P |s2cid= 130950517 }}Croatia;{{cite journal |last1=Bonacci |first1=O. |last2= Ljubenkov |first2=I. |last3=Roje-Bonacci |first3=T. |title=Karst flash floods: an example from the Dinaric karst (Croatia) |journal=Natural Hazards and Earth System Sciences |date=31 March 2006 |volume=6 |issue=2 |pages=195–203 |doi=10.5194/nhess-6-195-2006|bibcode= 2006NHESS...6..195B |doi-access= free }} Bosnia and Herzegovina; Slovenia; and Russia, where one-third of the total land area is underlain by karst.{{cite book |last1=Tolmachev |first1=Vladimir |last2=Leonenko |first2= Mikhail |title=Karst Management |chapter= Experience in Collapse Risk Assessment of Building on Covered Karst Landscapes in Russia |date=2011 |pages=75–102 |doi= 10.1007/978-94-007-1207-2_4|isbn= 978-94-007-1206-5 }}

File:AlapahaRiver2002.jpg flow of the Alapaha River near Jennings, Florida goes into a sinkhole leading to the Floridan Aquifer groundwater]]

File:Gouffre-v-hdr.jpg in France known since the 3rd c. and explored in 1889]]

File:240 Faithway Drive sinkhole, 2015.png

Sinkholes tend to occur in karst landscapes.{{Sfn|Tills|2013|p=182}} Karst landscapes can have up to thousands of sinkholes within a small area, giving the landscape a pock-marked appearance. These sinkholes drain all the water, so there are only subterranean rivers in these areas. Examples of karst landscapes with numerous massive sinkholes include Khammouan Mountains (Laos) and Mamo Plateau (Papua New Guinea).{{Cite web|url=http://www.cnc3.co.tt/about/what-sinkhole|title=What is a sinkhole?|website=CNC3|access-date=31 March 2016|date=14 March 2016}}{{cite web|url=http://www.wondermondo.com/Best/World/Sinkholes.htm|title=Largest and most impressive sinkholes of the world|publisher=Wondermondo|date=19 August 2010}} The largest known sinkholes formed in sandstone are Sima Humboldt and Sima Martel in Venezuela.

Some sinkholes form in thick layers of homogeneous limestone. Their formation is facilitated by high groundwater flow, often caused by high rainfall; such rainfall causes formation of the giant sinkholes in the Nakanaï Mountains, on the New Britain island in Papua New Guinea.{{cite web|url=http://www.wondermondo.com/Countries/Au/Papua/EastNewBritain/Nare.htm|title=Naré sinkhole|publisher=Wondermondo|date=5 August 2010}} Powerful underground rivers may form on the contact between limestone and underlying insoluble rock, creating large underground voids.

In such conditions, the largest known sinkholes of the world have formed, like the {{convert|662|m|ft|adj=mid|-deep}} Xiaozhai Tiankeng (Chongqing, China), giant sótanos in Querétaro and San Luis Potosí states in Mexico and others.{{cite journal |last=Zhu |first=Xuewen |author2=Chen, Weihai |title=Tiankengs in the karst of China |journal=Speleogenesis and Evolution of Karst Aquifers |year=2006 |volume=4 |pages=1–18 |url=http://www.speleogenesis.info/pdf/SG9/SG9_artId3290.pdf |issn=1814-294X |access-date=23 September 2010 |archive-date=13 March 2016 |archive-url=https://web.archive.org/web/20160313045041/http://www.speleogenesis.info/pdf/SG9/SG9_artId3290.pdf |url-status=dead }}

Unusual processes have formed the enormous sinkholes of Sistema Zacatón in Tamaulipas (Mexico), where more than 20 sinkholes and other karst formations have been shaped by volcanically heated, acidic groundwater.{{cite web|url=http://www.geo.utexas.edu/faculty/jmsharp/zacaton/default.htm|title=Sistema Zacatón|publisher=by Marcus Gary}}{{cite web|url=http://www.wondermondo.com/Countries/NA/Mexico/Tamaulipas/SistemaZacaton.htm|title=Sistema Zacatón|publisher=Wondermondo|date=3 July 2010}} This has produced not only the formation of the deepest water-filled sinkhole in the world—Zacatón—but also unique processes of travertine sedimentation in upper parts of sinkholes, leading to sealing of these sinkholes with travertine lids.

The U.S. state of Florida in North America is known for having frequent sinkhole collapses, especially in the central part of the state. Underlying limestone there is from 15 to 25 million years old. On the fringes of the state, sinkholes are rare or non-existent; limestone there is around 120,000 years old.{{Cite news | first=Tyler | last=Vazquez | title=The Hole Truth | url=https://www.floridatoday.com/story/news/2017/09/27/experts-say-sinkholes-unlikely-brevard-county/704151001/| newspaper=Florida Today | location=Melbourne, Florida| pages= 1A,2A | date=29 September 2017 | access-date=29 September 2017}}

The Murge area in southern Italy also has numerous sinkholes. Sinkholes can be formed in retention ponds from large amounts of rain.{{cite web|url=http://www.dot.ca.gov/hq/esc/geotech/geo_support/geophysics_geology/documents/geophysics_2002/114garman_sinkhole4.pdf|title=IDENTIFICATION AND DELINEATION OF SINKHOLE COLLAPSE HAZARDS IN FLORIDA USING GROUND PENETRATING RADAR AND ELECTRICAL RESISTIVITY IMAGING|author1=William L. Wilson|author2=K. Michael Garman|publisher=Subsurface Evaluations, Inc.|at=Case 3 – Mariner Boulevard|access-date=8 October 2016|archive-date=25 February 2017|archive-url=https://web.archive.org/web/20170225215949/http://www.dot.ca.gov/hq/esc/geotech/geo_support/geophysics_geology/documents/geophysics_2002/114garman_sinkhole4.pdf|url-status=dead}}

On the Arctic seafloor, methane emissions have caused large sinkholes to form.{{cite journal |last1=Paull |first1=Charles K. |last2=Dallimore |first2=Scott R. |last3=Jin |first3=Young Keun |last4=Caress |first4=David W. |last5=Lundsten |first5=Eve |last6=Gwiazda |first6=Roberto |last7=Anderson |first7=Krystle |last8=Hughes Clarke |first8=John |last9=Youngblut |first9=Scott |last10=Melling |first10=Humfrey |title=Rapid seafloor changes associated with the degradation of Arctic submarine permafrost |journal=Proceedings of the National Academy of Sciences |date=22 March 2022 |volume=119 |issue=12 |pages=e2119105119 |doi=10.1073/pnas.2119105119 |doi-access=free |pmid=35286188|pmc=8944826 |bibcode=2022PNAS..11919105P }}{{Cite web |author=Katie Hunt |title=Holes the size of city blocks are forming in the Arctic seafloor |url=https://www.cnn.com/2022/03/14/world/arctic-seafloor-holes-permafrost-scn/index.html |access-date=2022-03-15 |website=CNN|date=14 March 2022 }}

Sinkholes have been used for centuries as disposal sites for various forms of waste. A consequence of this is the pollution of groundwater resources, with serious health implications in such areas.{{cite book |last1=Erchul |first1=R.A. |year=1991 |chapter=Illegal disposal in sinkholes: The threat and the solution. |title=Appalachian Karst: Proceedings of the Appalachian Karst Symposium. 1991 |publisher=National Speleological Society |isbn=9780961509354}}{{cite journal |last1=Vesper |first1=D.J. |last2=Loop |first2=C.M. |last3=White |first3=W.B. |year=2001 |title=Contaminant transport in karst aquifers. |journal=Theoretical and Applied Karstology |volume=13 |number=14 |pages=101–111 |url=http://speleogenesis.info/directory/karstbase/pdf/seka_pdf4490.pdf |access-date=22 December 2020 |archive-date=7 March 2021 |archive-url=https://web.archive.org/web/20210307215719/http://speleogenesis.info/directory/karstbase/pdf/seka_pdf4490.pdf |url-status=dead }}

The Maya civilization sometimes used sinkholes in the Yucatán Peninsula (known as cenotes) as places to deposit precious items and human sacrifices.{{cite web | url=https://news.nationalgeographic.com/news/2014/01/140116-maya-mexico-yucatan-cenote-bones-haunted-taboo-archaeology-science/ | archive-url=https://web.archive.org/web/20140119212920/http://news.nationalgeographic.com/news/2014/01/140116-maya-mexico-yucatan-cenote-bones-haunted-taboo-archaeology-science/ | url-status=dead | archive-date=19 January 2014 | title="Haunted" Maya Underwater Cave Holds Human Bones | date=16 January 2014 | access-date=24 June 2019}}

When sinkholes are very deep or connected to caves, they may offer challenges for experienced cavers or, when water-filled, divers. Some of the most spectacular are the Zacatón cenote in Mexico (the world's deepest water-filled sinkhole), the Boesmansgat sinkhole in South Africa, Sarisariñama tepuy in Venezuela, the Sótano del Barro in Mexico, and in the town of Mount Gambier, South Australia. Sinkholes that form in coral reefs and islands that collapse to enormous depths are known as blue holes and often become popular diving spots.{{cite book|last=Rock|first=Tim|title=Diving & Snorkeling Belize|year=2007|publisher=Lonely Planet|location=Footscray, Vic.|isbn=9781740595315|page=65|edition=4th}}

{{clear left}}

File:Great Blue Hole.jpg near Ambergris Caye, Belize]]

Large and visually unusual sinkholes have been well known to local people since ancient times. Nowadays sinkholes are grouped and named in site-specific or generic names. Some examples of such names are listed below.{{cite web |url=http://www.wondermondo.com/Attractions/Sinkholes.htm |title=Sinkholes |date=19 August 2010 |publisher=Wondermondo}}

• Aven – In the south of France (this name means pit cave in the Occitan language).
• Black holes (not to be confused with cosmic black holes) – This term refers to a group of unique, round, water-filled pits in the Bahamas. These formations seem to be dissolved in carbonate mud from above, by the sea water. The dark color of the water is caused by a layer of phototropic microorganisms concentrated in a dense, purple colored layer at {{convert|15|to|20|m|ft|abbr=on}} depth; this layer "swallows" the light. Metabolism in the layer of microorganisms causes heating of the water. One of them is the Black Hole of Andros.{{cite web |url=http://www.wondermondo.com/Countries/NA/Bahamas/SouthAndros/AndrosBlackHole.htm |title=Black Hole of Andros |date=17 August 2010 |publisher=Wondermondo}}
• Blue holes – This name was initially given to the deep underwater sinkholes of the Bahamas but is often used for any deep water-filled pits formed in carbonate rocks. The name originates from the deep blue color of water in these sinkholes, which is created by the high clarity of the water and the great depth of the sinkholes; only the deep blue color of the visible spectrum can penetrate such depth and return after reflection.
• Cenote – This refers to the characteristic water-filled sinkholes in the Yucatán Peninsula, Belize and some other regions. Some of the cenotes are developed above the rim of the Chicxulub crater and helped to identify its presence.
• Dolina – Slovenian toponym internationally used for karst sinkholes. The original meaning is "valley" or "dale".{{Cite web |title=dolina |url=https://www.enciklopedija.hr/clanak/dolina |access-date=2024-10-11 |website=Hrvatska enciklopedija}}
• Foiba – Friulan Italian dialect word (from the Latin fŏvea: "pit" or "chasm"). The name is given to sinkholes in the frontier zone between the Italian region of Friuli-Venezia Giulia, Croatia and Slovenia, in the Karst Plateau.
• Sótanos – This name is given to several giant pits in several states of Mexico.
• Tiankengs – These are extremely large sinkholes, typically deeper and wider than {{convert|250|m|ft|abbr=on}}, with mostly vertical walls, most often created by the collapse of caverns. The term means sky holes in Chinese; many of this largest type of sinkhole are located in China.{{cite book |last=Waltham |first=Tony |title=Sinkholes and subsidence: karst and cavernous rocks in engineering and construction |year=2005 |publisher=Springer [u.a.] |location=Berlin [u.a.] |isbn=978-3540207252 |edition=1st |author2=Bell, Fred |author3=Culshaw, Martin }}{{rp|64}}
• Tomo – This term is used in New Zealand karst country to describe sinkholes.{{Cite web|url=https://waikatoregion.govt.nz/services/regional-services/regional-hazards-and-emergency-management/subsidence/|title=Subsidence|website=Waikato Regional Council|language=en-NZ|access-date=25 January 2018}}
• Vrtača, ponikva, dolac, dô – Croatian terms for sinkhole.{{Cite web |title=ponikva |url=https://www.enciklopedija.hr/clanak/ponikva |access-date=2024-10-11 |website=Hrvatska enciklopedija}}

The 2010 Guatemala City sinkhole formed suddenly in May of that year; torrential rains from Tropical Storm Agatha and a bad drainage system were blamed for its creation. It swallowed a three-story building and a house; it measured approximately {{convert|20|m|abbr=on}} wide and {{convert|30|m|abbr=on}} deep.{{Sfn|Tills|2013|p=184}} A similar hole had formed nearby in February 2007.{{cite magazine|last=Fletcher|first=Dan|title=Massive Sinkhole Opens in Guatemala|url=https://newsfeed.time.com/2010/06/01/giant-sinkhole-opens-in-guatemala-city/|magazine=Time|access-date=20 March 2013|date=1 June 2010}}{{cite news|last=Vidal|first=Luis|title=¿Que diablos provoco este escalofriante hoyo?|url=http://www.lun.com/Pages/NewsDetail.aspx?dt=2010-06-02&NewsID=95483&BodyID=0&PaginaId=14|access-date=20 March 2013|newspaper=Las Ultimas Noticias|date=2 June 2010|author2=Jorge Nunez|language=es}}{{cite magazine|last=Than|first=Ker|title=Sinkhole in Guatemala: Giant Could Get Even Bigger|url=http://news.nationalgeographic.com/news/2010/06/100601-sinkhole-in-guatemala-2010-world-science/|archive-url=https://web.archive.org/web/20100602110301/http://news.nationalgeographic.com/news/2010/06/100601-sinkhole-in-guatemala-2010-world-science/|url-status=dead|archive-date=2 June 2010|magazine=National Geographic|access-date=20 March 2013|date=1 June 2010}}

This large vertical hole is not a true sinkhole, as it did not form via the dissolution of limestone, dolomite, marble, or any other water-soluble rock.{{cite journal |doi=10.1144/1470-9236/07-211 |title=Sinkhole hazard case histories in karst terrains |year=2008 |last1=Waltham |first1=T. |journal=Quarterly Journal of Engineering Geology and Hydrogeology |volume=41 |issue=3 |pages=291–300|bibcode=2008QJEGH..41..291W |s2cid=128585380 }}{{cite journal|last=Halliday|first=W.R.|title=Pseudokarst in the 21st Century|journal=Journal of Cave and Karst Studies|year=2007|volume=69|issue=1|pages=103–113|url=http://www.caves.org/pub/journal/PDF/v69/cave-69-01-103.pdf|access-date=24 March 2013}} Instead, they are examples of "piping pseudokarst", created by the collapse of large cavities that had developed in the weak, crumbly Quaternary volcanic deposits underlying the city. Although weak and crumbly, these volcanic deposits have enough cohesion to allow them to stand in vertical faces and to develop large subterranean voids within them. A process called "soil piping" first created large underground voids, as water from leaking water mains flowed through these volcanic deposits and mechanically washed fine volcanic materials out of them, then progressively eroded and removed coarser materials. Eventually, these underground voids became large enough that their roofs collapsed to create large holes.

A crown hole is subsidence due to subterranean human activity, such as mining and military trenches.{{Cite web | url=https://www.gyproc.ie/subsidence-incident | title=Subsidence Incident | Gyproc | access-date=19 April 2020 | archive-date=30 September 2023 | archive-url=https://web.archive.org/web/20230930052133/https://www.gyproc.ie/subsidence-incident | url-status=dead }}{{Cite journal | url=https://www.rte.ie/news/regional/2020/0417/1132198-crownhole-monaghan/ | title=Crown hole appears in Magheracloone, Co Monaghan| journal=RTÉ News| date=17 April 2020| last1=Hussey| first1=Sinéad}} Examples have included, instances above World War I trenches in Ypres, Belgium; near mines in Nitra, Slovakia; a limestone quarry in Dudley, England;{{Cite web | url=https://www.birminghammail.co.uk/news/nostalgia/spare-thought-cricket-club-went-13767093 | title=The cricket club that went down the hole| date=16 October 2017}}{{cite journal |journal=Landscapes and Landforms of Hungary – World Geomorphological Landscapes |title=The Crater Lakes of Nagyhegyes|editor-first=Dénes |editor-last=Lóczy |publisher=Springer |year=2015 |isbn=978-3319089973 |page=247}} and above an old gypsum mine in Magheracloone, Ireland.

{{Further|List of sinkholes}}

File:Oman2-056_(8479895991).jpg in Oman]]

Some of the largest sinkholes in the world are:

• Boesmansgat – South African freshwater sinkhole, approximately {{convert|290|m|ft|abbr=on}} deep.{{cite journal|last=Beaumont|first=P.B.|author2=Vogel, J.C. |title=On a timescale for the past million years of human history in central South Africa|journal=South African Journal of Science|date=May–June 2006|volume=102|pages=217–228|issn=0038-2353|hdl=10204/1944}}
• Lake Kashiba – Zambia. About {{convert|3.5|ha|acre|abbr=off}} in area and about {{convert|100|m|ft|abbr=on}} deep.
• Blue Hole – Dahab, Egypt. A round sinkhole or blue hole, {{convert|130|m|ft|abbr=on}} deep. It includes an archway leading out to the Red Sea at {{convert|60|m|ft|abbr=on}}, which has been the site for many freediving and scuba attempts, the latter often fatal.{{cite book |last=Halls |first=Monty |url=https://archive.org/details/scubadiving0000hall/page/267 |title=Scuba diving |author2=Krestovnikoff, Miranda |publisher=DK Pub. |year=2006 |isbn=9780756619497 |edition=1st American |location=New York |page=[https://archive.org/details/scubadiving0000hall/page/267 267] |url-access=registration}}

• Akhayat sinkhole is in Mersin Province, Turkey. Its dimensions are about {{cvt|150|m}} in diameter with a maximum depth of {{cvt|70|m}}.
• Well of Barhout – A {{convert|112|m|ft|adj=on}} deep pit cave in Al-Mahara, Yemen.
• Bimmah Sinkhole (Hawiyat Najm, the Falling Star Sinkhole, Dibab Sinkhole) – Oman, approximately {{convert|30|m|ft|abbr=on}} deep.{{Cite journal|last1=Rajendran |first1=Sankaran |last2=Nasir |first2=Sobhi |year=2014 |title=ASTER mapping of limestone formations and study of caves, springs and depressions in parts of Sultanate of Oman |journal=Environmental Earth Sciences |volume=71 |issue=1 |pages=133–146, figure 9d (page 142), page 144 |doi=10.1007/s12665-013-2419-7 |bibcode=2014EES....71..133R |s2cid=128443371 |url=https://www.researchgate.net/publication/258244404}}{{Cite web|url=http://www.wondermondo.com/Countries/As/Oman/Muscat/Bimmah.htm|title=Bimmah sinkhole|date=3 February 2013|publisher=Wondermondo}}
• Teiq Sinkhole (Taiq, Teeq, Tayq) in Oman is one of the largest sinkholes in the world by volume: {{convert|90000000|m3|ft3|abbr=on}}. Several perennial wadis fall with spectacular waterfalls into this {{convert|250|m|ft|abbr=on}} deep sinkhole.{{Cite news |date=11 January 2015 |title=Dhofar caves: A tourist's paradise |url=http://www.muscatdaily.com/Archive/Oman/Dhofar-caves-A-tourist-s-paradise-3qrf/(language)/eng-GB |url-status=live |archive-url=https://web.archive.org/web/20161127234314/http://www.muscatdaily.com/Archive/Oman/Dhofar-caves-A-tourist-s-paradise-3qrf/(language)/eng-GB |archive-date=27 November 2016 |newspaper=Muscat Daily}}
• The Baatara gorge sinkhole and the Baatara gorge waterfall next to Tannourine in Lebanon
• Dashiwei Tiankeng in Guangxi, China, is {{convert|613|m|ft|abbr=on}} deep, with vertical walls. At the bottom is an isolated patch of forest with rare species.{{Cite book|author=Zhu, Xuewen |display-authors=etal |year=2003 |title=广西乐业大石围天坑群发现探测定义与研究 |trans-title=Dashiwei Tiankeng Group, Leye, Guangxi: discoveries, exploration, definition and research |publisher=Guangxi Scientific and Technical Publishers |location=Nanning, Guangxi, China |isbn=978-7-80666-393-6}}
• Shaanxi tiankeng cluster, in the Daba Mountains of southern Shaanxi, China, covers an area of nearly 5019 square kilometers{{Cite news|title=陕西发现天坑群地质遗迹并发现少见植物和飞猫 |trans-title=Tiankeng group of geological relics with rare plants and flying cats found in Shaanxi |publisher=Sohu.com Inc. |url=http://news.sohu.com/20161124/n474066542.shtml |archive-url=https://web.archive.org/web/20161125123153/http://news.sohu.com/20161124/n474066542.shtml |archive-date=25 November 2016 |url-status=live}} with the largest sinkhole being 520 meters in diameter and 320 meters deep.{{Cite web|date=25 November 2016 |title=时事新闻--解密汉中天坑群——改写地质历史的世界级"自然博物馆" |trans-title=Deciphering the Hanzhong tiankeng group – world-class "Nature Museum" |publisher=Hanzhong People's Municipal Government |url=http://www.zb.gov.cn/ssxw/zbxw/201611/t20161125_373374.html |archive-url=https://web.archive.org/web/20161127164343/http://www.zb.gov.cn/ssxw/zbxw/201611/t20161125_373374.html |archive-date=27 November 2016 |url-status=live}}
• Xiaozhai Tiankeng – Chongqing, China. Double nested sinkhole with vertical walls, {{convert|662|m|ft|abbr=on}} deep.{{Cite journal |last1=Zhu |first1=Xuewen |last2=Waltham |first2=Tony |year=2006 |title=Tiankeng: definition and description |journal=Speleogenesis and Evolution of Karst Aquifers |volume=4 |issue=1 |pages=1–8, Fig. 4. Structural interpretation of Xiaozhai Tiankeng, page 4 |url=http://speleogenesis.info/pdf/SG9/SG9_artId3292.pdf |access-date=28 November 2016 |archive-date=7 February 2017 |archive-url=https://web.archive.org/web/20170207065222/http://speleogenesis.info/pdf/SG9/SG9_artId3292.pdf |url-status=dead }}
• The Dragon Hole, located south of the Paracel Islands, is the deepest known underwater ocean sinkhole in the world. It is {{cvt|300.89|m}} deep.{{Cite news |title=China Exclusive: South China Sea "blue hole" declared world's deepest |url=http://news.xinhuanet.com/english/2016-07/23/c_135534400.htm |url-status=dead |archive-url=https://web.archive.org/web/20160724153235/http://news.xinhuanet.com/english/2016-07/23/c_135534400.htm |archive-date=24 July 2016 |newspaper=New China |publisher=Xinhua}}{{Cite news |title=Researchers just discovered the world's deepest underwater sinkhole in the South China Sea |url=https://www.washingtonpost.com/news/morning-mix/wp/2016/07/26/researchers-just-discovered-the-worlds-deepest-underwater-sinkhole-in-the-south-china-sea/ |newspaper=The Washington Post}}

• Dean's Blue Hole – Bahamas. The second deepest known sinkhole under the sea, depth {{convert|203|m|ft|abbr=on}}. Popular location for world championships of free diving, as well as recreational diving.

• Great Blue Hole – Belize. Spectacular, round sinkhole, {{convert|124|m|ft|abbr=on}} deep. Unusual features are tilted stalactites in great depth, which mark the former orientation of limestone layers when this sinkhole was above sea level.
• 2007 Guatemala City sinkhole
• 2010 Guatemala City sinkhole

• Hranice Abyss, in the Moravia region of the Czech Republic, is the deepest known underwater cave in the world. The lowest confirmed depth (as of 27 September 2016) is 473 m (404 m below the water level).
• Maqluba, in Malta is a sinkhole with a surface area of around 4,765 square metres (51,290 sq ft) situated in the village of Qrendi in Malta. The diameter is around 50m, the depth is around 15m, and the perimeter 300m.
• Pozzo del Merro, near Rome, Italy. At the bottom of an {{convert|80|m|ft|abbr=on}} conical pit, and approximately {{convert|400|m|ft|abbr=on}} deep, it is among the deepest sinkholes in the world (see Sótano del Barro below).{{Citation needed|date=November 2014}}
• Red Lake – Croatia. Approximately {{convert|530|m|ft|abbr=on}} deep pit with nearly vertical walls, contains an approximately {{convert|280|–|290|m|ft|abbr=on}} deep lake.
• Gouffre de Padirac – France. It is {{convert|103|m|ft|abbr=on}} deep, with a diameter of {{convert|33|m|ft|abbr=off}}. Visitors descend 75 m via a lift or a staircase to a lake allowing a boat tour after entering into the cave system which contains a 55 km subterranean river.
• Vouliagmeni – Greece. The sinkhole of Vouliagmeni is known as "The Devil Well",{{citation needed|date=April 2013}} because it is considered extremely dangerous. Four scuba divers have died in it.{{cite news|last=Schonauer|first=Scott|title=Missing American divers will be laid to rest after 30 years|url=http://www.stripes.com/news/missing-american-divers-will-be-laid-to-rest-after-30-years-1.66763|access-date=28 April 2013|newspaper=Stars and Stripes|date=21 July 2007|archive-date=4 October 2013|archive-url=https://web.archive.org/web/20131004215537/http://www.stripes.com/news/missing-american-divers-will-be-laid-to-rest-after-30-years-1.66763|url-status=dead}} Maximum depth of {{convert|35.2|m|ftin|abbr=on}} and horizontal penetration of {{convert|150|m|ft|abbr=on}}.
• Pouldergaderry – Ireland. This sinkhole is located in the townland of Kilderry South near Milltown, County Kerry at {{coord|52|7|57.5|N|9|44|45.4|W|source:enwiki-plaintext-parser|}}.{{Cite web|url=https://www.google.ie/maps/place/52%C2%B007%2757.5%22N+9%C2%B044%2745.4%22W/@52.1324101,-9.7467001,2000m/data=!3m1!1e3!4m2!3m1!1s0x0:0x0|title=52°07'57.5"N 9°44'45.4"W · Kilderry South, Co. Kerry, Ireland|website=52°07'57.5"N 9°44'45.4"W · Kilderry South, Co. Kerry, Ireland}}{{citation needed|date=March 2015}} The sinkhole, which is located in an area of karst bedrock, is approximately {{convert|80|m|ft}} in diameter and {{convert|30|m|ft}} deep with many mature trees growing on the floor of the hole. At the level of the surrounding ground, the sinkhole covers an area of approximately 1.3 acres. Its presence is indicated on Ordnance Survey maps dating back to 1829.{{cite web|url=http://maps.osi.ie/publicviewer/#V1,480483,599340,7,7|title=Shop.osi.ie Mapviewer|access-date=9 March 2015|archive-url=https://web.archive.org/web/20120829114800/http://maps.osi.ie/publicviewer/#V1,480483,599340,7,7|archive-date=29 August 2012|url-status=dead}}

• Cave of Swallows – San Luis Potosí. {{convert|372|m|ft|abbr=on}} deep, round sinkhole with overhanging walls.
• Puebla sinkhole – Santa Maria Zacatepec, Puebla. {{convert|400|ft|m|order=flip|abbr=on}} diameter and {{convert|50|ft|m|round=5|order=flip|abbr=on}} deep, it is still growing {{as of|June 2021|lc=y}}. 2021.{{cite web |last1=Guzman |first1=Joseph |title=A sinkhole larger than a football field has appeared in Mexico — and it's still growing |url=https://thehill.com/changing-america/sustainability/environment/557844-a-sinkhole-larger-than-a-football-field-has |website=TheHill |access-date=June 11, 2021 |language=en |date=2021-06-10}}
• Sima de las Cotorras – Chiapas. {{convert|160|m|ft|abbr=on}} across, {{convert|140|m|ft|abbr=on}} deep, with thousands of green parakeets and ancient rock paintings.
• Zacatón – Tamaulipas. Deepest water-filled sinkhole in world, {{convert|339|m|ft|abbr=on}} deep. {{explain|date=June 2013}}

• Grassy Cove – Cumberland County, Tennessee. {{convert|13.6|km2|sqmi|abbr=on}} in area and {{convert|42.7|m|ftin|abbr=on}} deep,{{cite web |author=Dunigan, Tom |title=Grassy Cove |url=http://tnlandforms.us/landforms/m.php?wpt=CUX001 |access-date=11 March 2014 |website=Tennessee Landforms}} a National Natural Landmark.

• Golly Hole or December Giant – Calera, Alabama. Appeared 2 December 1972. Approximately {{convert|300|by|325|ft|abbr=on}} and {{convert|120|ft|m|round=5|order=flip|abbr=on}} deep."[https://news.google.com/newspapers?id=cBIdAAAAIBAJ&sjid=MpwEAAAAIBAJ&pg=5787%2C5468505 Nation's largest sinkhole may be near Montevallo]" (29 March 1973) The Tuscaloosa News

• Amberjack Hole – blue hole located {{convert|30|mi|km|0|abbr=on|order=flip}} off the coast of Sarasota, Florida.
• Green Banana Hole – a blue hole located {{convert|50|mi|km|0|abbr=on|order=flip}} off the coast of Sarasota, Florida.
• Kingsley Lake – Clay County, Florida. {{convert|8.1|km2|acre|abbr=on}} in area, {{convert|27|m|ft|abbr=on}} deep and almost perfectly round.
• Winter Park Sinkhole – Winter Park, Florida. Appeared 8 May 1981. It was approximately {{convert|350|ft|m|abbr=on|order=flip}} wide and {{convert|75|ft|m|abbr=on|order=flip|round=5}} deep. It was notable as one of the largest recent sinkholes to form in the United States. It is now known as Lake Rose.{{Cite news |author=Huber, Red |date=13 November 2012 |title=Looking back at Winter Park's famous sinkhole |url=http://www.orlandosentinel.com/os-fla360-looking-back-at-winter-parks-famous-sinkhole-20121113-story.html |newspaper=Orlando Sentinel}}
• Devil's Millhopper – Gainesville, Florida. {{convert|120|ft|m|abbr=on|order=flip|round=5}} deep, {{convert|500|ft|m|abbr=on}} wide. Twelve springs, some more visible than others, feed a pond at the bottom.{{cite web |title=Devils Millhopper Geological State Park |url=http://www.floridastateparks.org/devilsmillhopper |url-status=dead |archive-url=https://web.archive.org/web/20150102012348/http://www.floridastateparks.org/devilsmillhopper/ |archive-date=2 January 2015 |access-date=3 May 2014 |publisher=Floridastateparks.org}}
• Bayou Corne sinkhole – Assumption Parish, Louisiana. About 25 acres in area{{cite news |last=Wines |first=Michael |title=Ground Gives Way, and a Louisiana Town Struggles to Find Its Footing |url=https://www.nytimes.com/2013/09/26/us/ground-gives-way-and-a-louisiana-town-struggles-to-find-its-footing.html |access-date=26 September 2013 |newspaper=New York Times |date=25 September 2013}} and {{convert|750|ft|m|-1|order=flip|abbr=on}} deep.
• Lake Peigneur – New Iberia, Louisiana. Original depth {{convert|11|ft|m|abbr=on|order=flip}}, currently {{convert|1300|ft|m|abbr=on|order=flip}} at Diamond Crystal Salt Mine collapse.{{cite report |url=https://babel.hathitrust.org/cgi/pt?id=uc1.31822029061140 |title=The Jefferson Island Mine inundation |author=Mine Safety and Health Administration |author-link=Mine Safety and Health Administration |date=1981-08-13 |access-date=2020-02-04}}
• Daisetta Sinkholes – Daisetta, Texas. Several sinkholes have formed, the most recent in 2008 with a maximum diameter of {{convert|620|ft|abbr=on}} and maximum depth of {{convert|150|ft|m|round=5|order=flip|abbr=on}}.{{cite news |last=Horswell |first=Cindy |title=Daisetta sinkhole still a mystery 8 months after it formed |url=http://www.chron.com/news/houston-texas/article/Daisetta-sinkhole-still-a-mystery-8-months-after-1605010.php |access-date=29 June 2013 |newspaper=Houston Chronicle |date=5 January 2009}}{{cite news|last=Blumenthal|first=Ralph|title=Sinkhole and Town: Now You See It|url=https://www.nytimes.com/2008/05/09/us/09sinkhole.html?em&ex=1210478400&en=d764ffeb80ef3667&ei=5087%0A&_r=0|access-date=29 June 2013|newspaper=The New York Times|date=9 May 2008}}
• The Blue Hole – Santa Rosa, New Mexico. The surface entrance is only {{convert|80|ft|m}} in diameter, it expands to a diameter of {{convert|130|ft|m}} at the bottom.
• Gypsum Sinkhole – Utah, in Capitol Reef National Park. Nearly {{convert|15|m|ft|abbr=on}} in diameter and approximately {{convert|60|m|ft|abbr=on}} deep.{{cite web|title=Cathedral Valley – Capitol Reef National Park|url=https://www.nps.gov/care/planyourvisit/cathedralvalley.htm|publisher=National Park Service, US Dept of Interior|access-date=24 March 2013}}

• Harwoods Hole – Abel Tasman National Park, New Zealand. {{convert|183|m|ft|abbr=on}} deep.

• Sima Humboldt – Bolívar, Venezuela. Largest sinkhole in sandstone, {{convert|314|m|ft|abbr=on}} deep, with vertical walls. Unique, isolated forest on bottom.
• In the western part of Cerro Duida, Venezuela, there is a complex of canyons with sinkholes. Deepest sinkhole is {{convert|450|m|ft|abbr=on}} deep (from lowest rim within canyon); total depth {{convert|950|m|ft|abbr=on}}.

{{Div col}}

• {{annotated link|List of sinkholes}}
• {{annotated link|Akhayat sinkhole}}
• {{annotated link|Blyvooruitzicht}}
• {{annotated link|Dolomite rock failure in South Africa}}
• {{annotated link|Caldera}}
• {{annotated link|Cennet and Cehennem}}
• {{annotated link|Dersios sinkhole}}
• {{annotated link|Dragon Hole}}
• {{annotated link|Estavelle}}
• {{annotated link|Garonne|Forau de Aigualluts}}
• {{annotated link|Gully}}
• {{annotated link|Lake-burst}}
• {{annotated link|Oak Island}}
• {{annotated link|Pingo}}
• {{annotated link|Pipe Creek Sinkhole}}
• {{annotated link|Turlough (lake)}}

{{Div col end}}

{{Reflist}}

{{USGS}}

Bibliography

• {{citation|title=Science Year|first=Tony |last=Tills|publisher=World Book, Inc.|year=2013|isbn=9780716605676}}

{{Commons category|Sinkholes}}

{{EB1911 poster|Swallow-hole}}

• [http://water.usgs.gov/edu/sinkholes.html US Geological Survey Water Science School page about sinkholes]
• [https://web.archive.org/web/20100613002846/http://www.telegraph.co.uk/earth/earthpicturegalleries/7818648/In-pictures-sinkholes-craters-and-collapsed-roads-around-the-world.html Daily Telegraph slide show of 31 sinkholes]
• [http://news.bbc.co.uk/2/hi/in_depth/7391071.stm Video of Sinkhole forming in Texas] (8 May 2008)
• Google [http://tnlandforms.us/google.php?trk=usholes map] of deepest "hole" for each state (Andy Martin)
• [http://tnlandforms.us/landforms/sinks.php Tennessee sinkholes] 54,000+ sinkholes
• {{cite news|last=James|first=Vincent|title=What are sinkholes, how do they form and why are we seeing so many?|url=https://www.independent.co.uk/news/science/sinkholes-what-are-they-how-do-they-form-and-why-are-we-seeing-so-many-9136235.html|work=The Independent|access-date=19 February 2014|date=18 February 2014}}

{{Natural disasters}}

{{Caves}}

{{Subterranea}}

{{Authority control}}

Category:Road hazards

Category:Dinaric karst formations

Category:Natural disasters