Sink holes are dominant in areas where the underground rock below the land surface is carbonate rock, limestone rock, sedimentary rock or any other type of rock, which is easily dissolved by underground water. The percolating underground water forms wide spaces and caverns below the land surface. Occurrence of sinkholes are dramatic as the above land surface remains intact until the below hollow surfaces and caverns formed by dissolving rocks get widened and finally the top surface gives away due to lack of bottom support. These collapses may be very small or very big eating away an entire house or huge chunks of roads. Size of the sinkholes varies from a few feet to hundreds of acres with a depth spanning from one feet to hundreds of feet. Given below are some interesting facts about sinkholes:
Fact 1: Sinkholes are of three types namely
(a) Solution sinkholes: The bedrock is exposed to the surface and dissolution occurs due to weathering. Natural depressions harbor surface water, which dissolves to create solution sinkholes.
(b) Subsidence sinkholes: These sinkholes are similar to solution sinkholes but the soluble bedrock is covered by a thin layer of soil or sediment, which gradually moves into the dissolved cavities of the bed rock.
(c) Collapse sinkholes: Sinkholes in which the surface material suddenly collapses into subsurface cavity or cave are called collapse sinkholes. These caves are formed by the dissolution of bedrock by underground water percolating through them over a long time.
Fact 2: The Minye sinkhole in Papua New Guinea and the Cedar Sink at Mammoth Cave National Park in Kentucky exhibit a visible opening into a cave below. Also an underground river or stream is visible at its bottom flowing from one side to the other.
Fact 3: Artificially sinkholes get created due to human activities like mining, salt cavern storage, leaking of old sewerage pipes, drain pipes and water pipes. Sinkholes also get created due to over pumping and extraction of groundwater and subsurface fluids. The construction of sub surface industrial storage ponds creates substantial weight and finally results in the collapse of supporting material causing a sinkhole.
Fact 4: The 662 meter (2,172 feet) deep Xiaozhai Tiankeng (Chongqing, China), giant sotanos in Queretaro and San Luis Potosi states in Mexico are the largest known sinkholes of the World.
Fact 5: Blue holes are the name given to deep water filled pits formed in carbonate rocks. The name was initially given to deep under water sinkholes in Bahamas. Noticeably high depths of the sinkholes impart it a dark blue color and hence the name is derived.
Fact 6: Usually the roof of the underground cave collapses and results in the formation of a ‘cenote’, exposing underground water to surface. They are around 2,000 in numbers in the Yucatan Peninsula of Mexico. These are the major source of fresh water here and the ancient Mayans believed that ‘cenotes’ are passageways to underworld.
Fact 7: Sinkholes are very prevalent in the land surrounding the Dead Sea in the Middle East due to the presence of rock salt, which is easily soluble in water. Unaware of this many tourists and scientists studying sinkholes have fallen into them and have been injured.
Fact 8: Little salt spring is a underwater sinkhole in Florida and the archaeological study of which has revealed that it was an ancient butcher shop, where hunters killed animals and prepared the meat nearly 8,000 to 9,000 years ago.
Fact 9: Florida sits on an unbroken bed of limestone. Hence sinkholes are a common problem in Florida, particularly in Central Florida. It is called the sinkhole alley with two thirds the insurance claims coming from Florida alone. Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania are the other states with the problem of sinkholes.
Fact 10: Tampa, Florida on 28th February 2013 witnessed a giant sink hole under the bedroom of a man named Jeffery Bush. The man was completely swallowed by the sink hole as he slept. His body was never found.