Asinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer todoline, enclosed depressions that are also known asshakeholes, and to openings where surface water enters into underground passages known asponor,swallow hole orswallet.[1][2][3][4] Acenote is a type of sinkhole that exposesgroundwater underneath.[4]Sink, andstream sink are more general terms for sites that drain surface water, possibly by infiltration into sediment or crumbled rock.[2]
Most sinkholes are caused bykarst processes – the chemical dissolution ofcarbonate rocks, collapse orsuffosion processes.[1][5] Sinkholes are usually circular and vary in size from tens to hundreds ofmeters both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may form gradually or suddenly, and are found worldwide.[2][1]
Sinkholes near theDead Sea, formed when underground salt is dissolved by freshwater intrusion, due to continuing sea-level drop.Collapse sinkhole inChinchón, Spain.
Sinkholes may capture surfacedrainage 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.[6][7]
The formation of sinkholes involves natural processes oferosion[8] or gradual removal of slightly soluble bedrock (such aslimestone) bypercolating water, thecollapse of acave roof, or a lowering of thewater table.[9] Sinkholes often form through the process ofsuffosion.[10] For example, groundwater may dissolve the carbonate cement holding thesandstone 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 inPapua New Guinea orCedar Sink atMammoth Cave National Park inKentucky, anunderground 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 othercarbonate rock,salt beds, or in other soluble rocks, such asgypsum,[11] that can be dissolved naturally by circulatingground water. Sinkholes also occur insandstone andquartzite terrains.
As the rock dissolves, spaces andcaverns 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.[12]
A 32 feet deep collapse formed by rainwater leaking through pavement and carrying soil into a ruptured sewer pipe in the parking lot atGeorgia Tech inAtlanta, Georgia in 2005.
Collapses, commonly incorrectly labeled as sinkholes, also occur due to human activity, such as the collapse of abandonedmines and salt cavern storage in salt domes in places likeLouisiana,Mississippi, andTexas, in the United States. More commonly, collapses occur inurban areas due towater main breaks orsewer collapses when oldpipes 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.[15]
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.[15]
Man-made activities and land alterations that cause water-level fluctuations accelerate cover-collapse sinkholes
TheU.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."[15] 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.[17]: 2 [18][16]: 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 soilcohesion. 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.[19]: 52–53
Induced sinkholes occur where human activity alters how surface waterrecharges 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.[17]: 26–29 The increased runoff from the impervious surfaces of roads, roofs, and parking lots also accelerate man-induced sinkhole collapses.[16]: 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.[17]: 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".[20]: xii [16]: 17 and 104 TheAmerican 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.[19]: 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.[21] Where large cavities exist in the limestone large surface collapses can occur, such theWinter Park, Florida sinkhole collapse.[16]: 91–92 Recommendations for land uses in karst areas should avoid or minimize alterations of the land surface and natural drainage.[17]: 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.[19]: 88 In karst areas the traditional foundation evaluations (bearing capacity andsettlement) of the ability of soil to support a structure must be supplemented bygeotechnical site investigation for cavities and defects in the underlying rock.[19]: 113 Since the soil/rock surface in karst areas are very irregular the number of subsurface samples (borings andcore samples) required per unit area is usually much greater than in non-karst areas.[19]: 98–99
More than three acres of forest suddenly disappeared into this "December Giant" sinkhole inMontevallo, 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.[22] The greatest amount of karst sinkhole damage in the United States occurs in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.[23] The largest recent sinkhole in the USA is possibly one that formed in 1972 inMontevallo, 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 130 m (425 ft) long, 105 m (350 ft) wide and 45 m (150 ft) deep.[17]: 1–2 [19]: 61–63 [24]
Sinkholes tend to occur in karst landscapes.[12] 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 onlysubterranean rivers in these areas. Examples of karst landscapes with numerous massive sinkholes includeKhammouan Mountains (Laos) andMamo Plateau (Papua New Guinea).[28][29] The largest known sinkholes formed in sandstone areSima Humboldt andSima Martel inVenezuela.[29]
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 theNakanaï Mountains, on theNew Britain island in Papua New Guinea.[30] Powerful underground rivers may form on the contact between limestone and underlying insoluble rock, creating large underground voids.
Unusual processes have formed the enormous sinkholes ofSistema Zacatón inTamaulipas (Mexico), where more than 20 sinkholes and other karst formations have been shaped by volcanically heated, acidic groundwater.[32][33] This has produced not only the formation of the deepest water-filled sinkhole in the world—Zacatón—but also unique processes oftravertine sedimentation in upper parts of sinkholes, leading to sealing of these sinkholes with travertine lids.[33]
The U.S. state ofFlorida 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.[34]
TheMurge area in southern Italy also has numerous sinkholes. Sinkholes can be formed in retention ponds from large amounts of rain.[35]
Sinkholes have been used for centuries as disposal sites for various forms ofwaste. A consequence of this is thepollution of groundwater resources, with serious health implications in such areas.[38][39]
When sinkholes are very deep or connected to caves, they may offer challenges for experiencedcavers or, when water-filled,divers. Some of the most spectacular are theZacatón cenote in Mexico (the world's deepest water-filled sinkhole), theBoesmansgat sinkhole in South Africa,Sarisariñamatepuy in Venezuela, the Sótano del Barro in Mexico, and in the town ofMount Gambier, South Australia. Sinkholes that form in coral reefs and islands that collapse to enormous depths are known asblue holes and often become popular diving spots.[41]
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.[42]
Aven – In the south of France (this name means pit cave in theOccitan language).
Black holes (not to be confused with cosmicblack 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 15 to 20 m (49 to 66 ft) 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.[43]
Blue holes – This name was initially given to the deep underwater sinkholes of theBahamas 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 visiblespectrum can penetrate such depth and return after reflection.
Cenote – This refers to the characteristic water-filled sinkholes in theYucatán Peninsula,Belize and some other regions. Some of the cenotes are developed above the rim of theChicxulub crater and helped to identify its presence.
Dolina – Slovenian toponym internationally used for karst sinkholes. The original meaning is "valley" or "dale".[44]
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 ofFriuli-Venezia Giulia,Croatia andSlovenia, in theKarst 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 250 m (820 ft), with mostly vertical walls, most often created by the collapse of caverns. The term meanssky holes in Chinese; many of this largest type of sinkhole are located in China.[20]: 64
Tomo – This term is used in New Zealand karst country to describe sinkholes.[45]
Vrtača,ponikva,dolac,dô – South Slavic terms for sinkhole.[44][46]
The2010 Guatemala City sinkhole formed suddenly in May of that year; torrential rains fromTropical Storm Agatha and a bad drainage system were blamed for its creation. It swallowed a three-story building and a house; it measured approximately 20 m (66 ft) wide and 30 m (98 ft) deep.[47] A similar hole had formed nearby in February 2007.[48][49][50]
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.[51][52] Instead, they are examples of "piping pseudokarst", created by the collapse of large cavities that had developed in the weak, crumblyQuaternary 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 leakingwater 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.[51]
Blue Hole – Dahab, Egypt. A round sinkhole or blue hole, 130 m (430 ft) deep. It includes an archway leading out to the Red Sea at 60 m (200 ft), which has been the site for many freediving and scuba attempts, the latter often fatal.[58]
Akhayat sinkhole is inMersin Province, Turkey. Its dimensions are about 150 m (490 ft) in diameter with a maximum depth of 70 m (230 ft).
Dashiwei Tiankeng inGuangxi, China, is 613 m (2,011 ft) deep, with vertical walls. At the bottom is an isolated patch of forest with rare species.[61]
TheDragon Hole, located south of theParacel Islands, is the deepest known underwater ocean sinkhole in the world. It is 300.89 m (987.2 ft) deep.[62][63]
Teiq Sinkhole (Taiq, Teeq, Tayq) in Oman is one of the largest sinkholes in the world by volume: 90,000,000 m3 (3.2×109 cu ft). Several perennialwadis fall with spectacular waterfalls into this 250 m (820 ft) deep sinkhole.[66]
Dean's Blue Hole – Bahamas. The second deepest known sinkhole under the sea, depth 203 m (666 ft). Popular location for world championships offree diving, as well as recreational diving.
Great Blue Hole – Belize. Spectacular, round sinkhole, 124 m (407 ft) deep. Unusual features are tilted stalactites in great depth, which mark the former orientation of limestone layers when this sinkhole was above sea level.
Hranice Abyss, in theMoravia 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, inMalta 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 80 m (260 ft) conical pit, and approximately 400 m (1,300 ft) deep, it is among the deepest sinkholes in the world (see Sótano del Barro below).[citation needed]
Red Lake –Croatia. Approximately 530 m (1,740 ft) deep pit with nearly vertical walls, contains an approximately 280–290 m (920–950 ft) deep lake.
Gouffre de Padirac – France. It is 103 m (338 ft) deep, with a diameter of 33 metres (108 feet). 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] because it is considered extremely dangerous. Four scuba divers have died in it.[68] Maximum depth of 35.2 m (115 ft 6 in) and horizontal penetration of 150 m (490 ft).
The Blue Hole –Santa Rosa, New Mexico. The surface entrance is only 80 feet (24 m) in diameter, it expands to a diameter of 130 feet (40 m) at the bottom.
Daisetta Sinkholes –Daisetta, Texas. Several sinkholes have formed, the most recent in 2008 with a maximum diameter of 620 ft (190 m) and maximum depth of 45 m (150 ft).[73][74]
Devil's Millhopper –Gainesville, Florida. 35 m (120 ft) deep, 500 ft (150 m) wide. Twelve springs, some more visible than others, feed a pond at the bottom.[75]
Golly Hole or December Giant –Calera, Alabama. Appeared 2 December 1972. Approximately 300 by 325 ft (91 by 99 m) and 35 m (120 ft) deep.[76]
Kingsley Lake –Clay County, Florida. 8.1 km2 (2,000 acres) in area, 27 m (89 ft) deep and almost perfectly round.
Lake Peigneur –New Iberia, Louisiana. Original depth 3.4 m (11 ft), currently 400 m (1,300 ft) at Diamond Crystal Salt Mine collapse.[79]
Winter Park Sinkhole –Winter Park, Florida. Appeared 8 May 1981. It was approximately 110 m (350 ft) wide and 25 m (75 ft) deep. It was notable as one of the largest recent sinkholes to form in the United States. It is now known as Lake Rose.[80]
Sima Humboldt –Bolívar, Venezuela. Largest sinkhole in sandstone, 314 m (1,030 ft) deep, with vertical walls. Unique, isolated forest on bottom.
In the western part ofCerro Duida, Venezuela, there is a complex of canyons with sinkholes. Deepest sinkhole is 450 m (1,480 ft) deep (from lowest rim within canyon); total depth 950 m (3,120 ft).
^abcd"Sinkholes".Water Science School. U.S. Geological Survey. Retrieved29 May 2019.
^abcdeBenson, Richard C.; Yuhr, Lynn B. (2015).Site Characterization in Karst and Pseudokarst Terraines: Practical Strategies and Technology for Practicing Engineers, Hydrologists and Geologists. Dordrecht: Springer.doi:10.1007/978-94-017-9924-9.ISBN978-94-017-9923-2.S2CID132318001.
^abWaltham, Tony; Bell, Fred; Culshaw, Martin (2005).Sinkholes and subsidence: karst and cavernous rocks in engineering and construction (1st ed.). Berlin [u.a.]: Springer [u.a.]ISBN978-3540207252.
^Tolmachev, Vladimir; Leonenko, Mikhail (2011). "Experience in Collapse Risk Assessment of Building on Covered Karst Landscapes in Russia".Karst Management. pp. 75–102.doi:10.1007/978-94-007-1207-2_4.ISBN978-94-007-1206-5.
^Erchul, R.A. (1991). "Illegal disposal in sinkholes: The threat and the solution.".Appalachian Karst: Proceedings of the Appalachian Karst Symposium. 1991. National Speleological Society.ISBN9780961509354.
^Vesper, D.J.; Loop, C.M.; White, W.B. (2001)."Contaminant transport in karst aquifers"(PDF).Theoretical and Applied Karstology.13 (14):101–111. Archived fromthe original(PDF) on 7 March 2021. Retrieved22 December 2020.
^Lóczy, Dénes, ed. (2015). "The Crater Lakes of Nagyhegyes".Landscapes and Landforms of Hungary – World Geomorphological Landscapes.Springer: 247.ISBN978-3319089973.
^Beaumont, P.B.; Vogel, J.C. (May–June 2006). "On a timescale for the past million years of human history in central South Africa".South African Journal of Science.102:217–228.hdl:10204/1944.ISSN0038-2353.
^"陕西发现天坑群地质遗迹并发现少见植物和飞猫" [Tiankeng group of geological relics with rare plants and flying cats found in Shaanxi]. Sohu.com Inc.Archived from the original on 25 November 2016.
^"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"" [Deciphering the Hanzhong tiankeng group – world-class "Nature Museum"]. Hanzhong People's Municipal Government. 25 November 2016.Archived from the original on 27 November 2016.
^Zhu, Xuewen; Waltham, Tony (2006)."Tiankeng: definition and description"(PDF).Speleogenesis and Evolution of Karst Aquifers.4 (1):1–8, Fig. 4. Structural interpretation of Xiaozhai Tiankeng, page 4. Archived fromthe original(PDF) on 7 February 2017. Retrieved28 November 2016.
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