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Sinkhole

Article Discussion

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File:07 Imotski Crveno Jezero (1).jpg
The Red Lake sinkhole in Croatia

A sinkhole 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 to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water enters into underground passages known as ponor, swallow hole or swallet.<ref name=":0">Template:Cite book</ref><ref name=":1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite book</ref><ref name=":2">Template:Cite journal</ref> A cenote is a type of sinkhole that exposes groundwater underneath.<ref name=":2" /> Sink, and stream sink are more general terms for sites that drain surface water, possibly by infiltration into sediment or crumbled rock.<ref name=":1" />

Most sinkholes are caused by karst processes – the chemical dissolution of carbonate rocks, collapse or suffosion processes.<ref name=":0" /><ref name="bgs">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Sinkholes are usually circular and vary in size from tens to hundreds of meters 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.<ref name=":1" /><ref name=":0" />

FormationEdit

File:Dead Sea sinkhole by David Shankbone.jpg
Sinkholes near the Dead Sea, formed when underground salt is dissolved by freshwater intrusion, due to continuing sea-level drop.
File:Chinchón dolina c1991.jpg
Collapse sinkhole in Chinchón, Spain.

Natural processesEdit

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.<ref>Template:Cite news</ref><ref>Template:Cite journal</ref>

The formation of sinkholes involves natural processes of erosion<ref>Template:Cite book</ref> 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.Template:Sfn Sinkholes often form through the process of suffosion.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.Template:Sfn

Space and planetary bodiesEdit

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.<ref name="NAT-20150702">Template:Cite journal</ref><ref name="AP-20150701">Template:Cite news</ref>

Artificial processesEdit

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File:Sinkhole.jpg
A Template:Convert collapse formed by rainwater leaking through pavement and carrying soil into a ruptured sewer pipe in the parking lot at Georgia Tech 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.

ClassificationEdit

Solution sinkholesEdit

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.<ref name=USGSsinkholesweb>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

USGS dissolution sinkhole.

Cover-subsidence sinkholesEdit

Cover-subsidence sinkholes form where voids in the underlying limestone allow more settling of the soil to create larger surface depressions.<ref name=USGSsinkholesweb />

USGS cover-subsidence sinkhole.

Cover-collapse sinkholesEdit

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.<ref name=USGSsinkholesweb />

USGS cover-subsidence sinkhole.

Pseudokarst sinkholesEdit

Pseudokarst sinkholes resemble karst sinkholes but are formed by processes other than the natural dissolution of rock.<ref name=SiteCharacterizationBenson />Template:Rp

Human-accelerated sinkholesEdit

File:Subsurface erosion of soil into karst conduit by water level fluctuation.jpg
Man-made activities and land alterations that cause water-level fluctuations accelerate cover-collapse sinkholes

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."<ref name= USGSsinkholesweb /> 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.<ref name= SinkholesResultingFromMan>Template:Cite book</ref>Template:Rp<ref>Template:Cite book</ref><ref name= SiteCharacterizationBenson>Template:Cite book</ref>Template:Rp 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.<ref name= BuildingOnSinkholes>Template:Cite book</ref>Template:Rp

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.<ref name= "SinkholesResultingFromMan" />Template:Rp The increased runoff from the impervious surfaces of roads, roofs, and parking lots also accelerate man-induced sinkhole collapses.<ref name= "SiteCharacterizationBenson" />Template:Rp

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.<ref name= SinkholesResultingFromMan />Template:Rp 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".<ref name= Waltham2005 />Template:Rp<ref name= SiteCharacterizationBenson />Template:Rp 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.<ref name= BuildingOnSinkholes />Template:Rp

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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Where large cavities exist in the limestone large surface collapses can occur, such the Winter Park, Florida sinkhole collapse.<ref name= SiteCharacterizationBenson />Template:Rp Recommendations for land uses in karst areas should avoid or minimize alterations of the land surface and natural drainage.<ref name= SinkholesResultingFromMan />Template:Rp

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.<ref name= BuildingOnSinkholes />Template:Rp 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.<ref name=BuildingOnSinkholes/>Template:Rp 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.<ref name=BuildingOnSinkholes/>Template:Rp

File:December Giant sinkhole collapse USGS 1972.jpg
More than three acres of forest suddenly disappeared into this "December Giant" sinkhole in Montevallo, 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.<ref>Template:Cite book</ref> The greatest amount of karst sinkhole damage in the United States occurs in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.<ref>Template:Cite journal</ref> 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 Template:Convert long, Template:Convert wide and Template:Convert deep.<ref name= SinkholesResultingFromMan />Template:Rp<ref name=BuildingOnSinkholes />Template:Rp<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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;<ref>Template:Cite journal</ref>Croatia;<ref>Template:Cite journal</ref> Bosnia and Herzegovina; Slovenia; and Russia, where one-third of the total land area is underlain by karst.<ref>Template:Cite book</ref>

OccurrenceEdit

File:AlapahaRiver2002.jpg
The entire surface water flow of the Alapaha River near Jennings, Florida goes into a sinkhole leading to the Floridan Aquifer groundwater
File:Gouffre-v-hdr.jpg
Gouffre de Padirac in France known since the 3rd c. and explored in 1889
File:240 Faithway Drive sinkhole, 2015.png
A Floridian sinkhole in 2015

Sinkholes tend to occur in karst landscapes.Template:Sfn 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).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=wondermondo>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The largest known sinkholes formed in sandstone are Sima Humboldt and Sima Martel in Venezuela.<ref name=wondermondo/>

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.<ref name=wondermondo2>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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 Template:Convert Xiaozhai Tiankeng (Chongqing, China), giant sótanos in Querétaro and San Luis Potosí states in Mexico and others.<ref name="wondermondo"/><ref name=Zhu_tiankeng>Template:Cite journal</ref>

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.<ref name=gary>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=wondermondo3>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref name=wondermondo3 />

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.<ref>Template:Cite news</ref>

The Murge area in southern Italy also has numerous sinkholes. Sinkholes can be formed in retention ponds from large amounts of rain.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

On the Arctic seafloor, methane emissions have caused large sinkholes to form.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Human usesEdit

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.<ref>Template:Cite book</ref><ref>Template:Cite journal</ref>

The Maya civilization sometimes used sinkholes in the Yucatán Peninsula (known as cenotes) as places to deposit precious items and human sacrifices.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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.<ref name=Rock_DivingBelize>Template:Cite book</ref> Template:Clear left

Local namesEdit

File:Great Blue Hole.jpg
The Great Blue Hole 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.<ref name=wondermondo4>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

  • 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 Template:Convert 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.<ref name=wondermondo5>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

  • 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".<ref name=":3">{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

  • 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 Template:Convert, 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.<ref name=Waltham2005>Template:Cite book</ref>Template:Rp
  • Tomo – This term is used in New Zealand karst country to describe sinkholes.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

  • Vrtača, ponikva, dolac, dô – Croatian terms for sinkhole.<ref name=":3" /><ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

Piping pseudokarstEdit

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 Template:Convert wide and Template:Convert deep.Template:Sfn A similar hole had formed nearby in February 2007.<ref name=Time_guathole>Template:Cite magazine</ref><ref name=LUN_quediablos>Template:Cite news</ref><ref name=NatGeo_guathole>Template:Cite magazine</ref>

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.<ref name="Waltham2008">Template:Cite journal</ref><ref name=Halliday2007>Template:Cite journal</ref> 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.<ref name="Waltham2008"/>

Crown holeEdit

A crown hole is subsidence due to subterranean human activity, such as mining and military trenches.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="magheracloone">Template:Cite journal</ref> Examples have included, instances above World War I trenches in Ypres, Belgium; near mines in Nitra, Slovakia;<ref name="LLHungary"/> a limestone quarry in Dudley, England;<ref name="LLHungary">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref> and above an old gypsum mine in Magheracloone, Ireland.<ref name="magheracloone"/>

Notable examplesEdit

Template:Further

File:Oman2-056 (8479895991).jpg
Bimmah or Falling Star Sinkhole in Oman

Some of the largest sinkholes in the world are:<ref name=wondermondo/>

AfricaEdit

AsiaEdit

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CaribbeanEdit

Central AmericaEdit

EuropeEdit

|CitationClass=web }}</ref>Template:Citation needed The sinkhole, which is located in an area of karst bedrock, is approximately Template:Convert in diameter and Template:Convert 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

North AmericaEdit

MexicoEdit

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United StatesEdit

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OceaniaEdit

South AmericaEdit

See alsoEdit

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ReferencesEdit

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Bibliography

External linksEdit

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