Where do Sinkholes Occur?
As is clear from the description of their formation, sinkholes have a strong relationship with rock type. Mainly associated with limestone, sinkholes are equally likely to occur in other easily dissolved rocks – so-called evaporites – such as areas with considerable underground deposits of salt or gypsum. Knowing this, it’s possible to map areas of high potential – and, as the USGS map shows, these types of rock occur across large areas of the USA – including Florida, which is largely composed of limestone rocks.
Quoted on National Geographic, the USGS’s Randall Orndorff summarized just some of the areas at risk in the US. “If you’re talking about limestone, you’re talking about the eastern U.S…the Great Valley, from Pennsylvania—even eastern New York…down through Tennessee to Alabama…the Ozarks of Missouri. And Indiana. And the southeastern corner of Minnesota.”
And that’s just limestone: Large parts of the U.S. are underlain by evaporite deposits – although it’s also worth noting that as many of these are buried at considerable depth the likelihood of dramatic collapse is decreased, especially where the climate is dry.
What Causes Sinkholes: Man or Nature?
It’s long-established that human activity can cause subsidence and damage – think of rows of miners’ cottages leaning drunkenly to one side. The principle which causes this subsidence is pretty much the same as for sinkholes – creation of a subterranean void which then collapses.
There’s disturbing evidence, however, for a human influence in sinkholes, too. In its guidance note Land Subsidence in the United States the USGS points out that huge areas are already subject to subsidence and that “more than 80 percent of the identified subsidence in the Nation is a consequence of our exploitation of underground water”.
And this includes sinkholes. With eerie prescience, the guidance note examines the situation in eastern Florida, the area where Jeffrey Bush lived and died. “In west-central Florida and elsewhere,” it notes “[sinkholes’] increasing frequency corresponds to the accelerated development of ground-water and land resources. Usually little more than a nuisance, new sinkholes can sometimes cause substantial property damage and structural problems for buildings and roads.”
Florida Sinkhole: Will it Happen Again?
If our ongoing use of groundwater is contributing to the sinkhole phenomenon, what are the long-term effects? Although there’s no comprehensive evidence for increasing frequency of sinkholes, it appears that human interference may well be amplifying the likelihood of this natural phenomenon occurring – and at a potential cost to life.
Berlin, Jeremy. Sinkhole Science – A Primer. National Geographic Accessed 5 March 2013.
Galloway, D., Jones, R. and Ingebritsen S.E. U.S. Geological Survey Circular 1182 Land Subsidence in the United States. Accessed 5 March 2013.
USGS. Sinkholes. Water Science School. Accessed 5 March 2013.
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