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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.
Subsidence frequently causes major problems in karst terrains, where dissolution of limestone by fluid flow in the subsurface creates voids (i.e., caves).If the roof of a void becomes too weak, it can collapse and the overlying rock and earth will fall into the space, causing subsidence at the surface.
[2] [1] Suffosion sinkholes are normally associated with karst topography although they may form in other types of rock including chalk, gypsum and basalt. In the karst of the UK's Yorkshire Dales, numerous surface depressions known locally as "shakeholes" are the result of glacial till washing into fissures in the underlying limestone.
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The problems had been reported in 2018 and noted as "much worse" in April 2021. A $15 million program of remedial works had been approved before the collapse, but the main structural work had not started. Other possible factors include land subsidence, insufficient reinforcing steel, and corruption during construction.
Sinkholes can range in size from a few feet wide to hundreds of acres, and anywhere from 1 to 100 feet or more deep. Sinkholes can swallow up cars, parts of roads and even houses.
Sinkholes can be classified on the basis of the processes by which they are formed: dissolution, cover-subsidence, and cover-collapse. Formation of sinkholes can be accelerated by intense withdrawals of groundwater over short periods of time, such as those caused by pumping for frost-protection of winter crops in west-central Florida.
A huge sinkhole in a street in Surrey is continuing to grow and swallow up more road, with the county council declaring a major incident. The original hole first appeared in Godstone High Street ...