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Most Franklin County residents probably don’t stay awake at night worrying about an encounter with a sinkhole, like the one that wreaked havoc on the Bowling Green, Ky., National Corvette Museum, but such earthen collapses on a smaller scale aren’t uncommon in the immediate area.
John Woodall, Franklin County Highway Department superintendent, said two had occurred in the past two weeks on rural roads, requiring personnel to make repairs.
None have occurred in the immediate area, like the Corvette Museum sinkhole that swallowed eight historic cars, but the most recent one happened on March 1 on Garrett Lane, requiring eight tons of gravel to fill underneath the pavement.
The sinkhole left a small opening toward the middle of the pavement and extended underneath, slightly past the road’s edge.
From an initial glimpse, it didn’t look that bad, but the hole was several feet deep, leaving a cavity underneath the pavement that could have been hazardous if the surface would have collapsed, Woodall said. He added it was fortunate no one had driven over it and experienced what could have happened if the pavement would have collapsed.
The other sinkhole occurred around Feb. 17 on a gravel-based Cole Lane, a short distance from the Garrett Lane collapse. It required 20 tons of gravel to fill it.
Woodall said the two sinkholes appear to be in the same fault area and could have been spawned from a small-scale earthquake around Valentine’s Day that was barely noticed.
“I don’t really know if the earthquake had anything to do with them,” Woodall said, referring to the sinkholes. “But it all happened about the same time, so it makes you wonder.”
Another larger one occurred in December 2010 on State Route 422 near Holder’s Cove Road in Winchester that was about 30 feet deep and 15 feet in diameter that required the road to be temporarily shut down.
A sinkhole also occurred several years back along Gum Creek Road in Decherd that remains largely in its fallen state and serves as a quick reminder how fast topography can change when the area below the surface land gives way.
While sinkholes in Tennessee have had less devastating effects, Florida has a routine problem with them and provides information on the state’s http://www.dep.state.fl.us/geology/feedback/faq.htm#3 website.
The website explains that sinkholes form in karst terrain — a type of topography that is formed by dissolution of bedrock in areas underlain by limestone, dolostone or, as in some western states, gypsum.
Such terrain has underground drainage systems that are reflected on the surface as sinkholes, springs, disappearing streams or even caves.
The term karst refers to the terrain, and the term sinkhole is one of the types of drainage features reflected by that type of terrain.
Sinkholes occur mainly from the collapse of surface sediments into underground voids and cavities in the limestone bedrock.
The website also says that slightly acidic groundwater slowly dissolves cavities and caves in the limestone over many years.
When the cavity enlarges to where its ceiling can no longer support the weight of overlying sediments, the earth collapses into the cavity.
In the less catastrophic type of sinkhole, a bowl-shaped depression forms at the surface, usually over a considerable period of time, as surface sediments ravel downward into small cavities in the bedrock.
The website says well drilling data suggests that much of the underlying bedrock in Florida contains cavities of differing size and depth. However, relatively few ever collapse and directly effect roads or dwellings.