The ground suddenly opening beneath our feet is the stuff of nightmares.
In recent weeks, a spate of those bad-dreams-come-true have drawn national attention when the earth seemingly swallowed a man in his Florida bedroom and a golfer in Illinois.
After the widespread coverage of those sinkholes and others, some experts say the phenomena may be scarier in thought than in reality.
Only about 20 percent of the country has underground geology that favors the formation of natural sinkholes, the U.S. Geological Survey says. But in developed areas, any pipeline or sewer can collapse in the right circumstances.
"I'd guess there is this primal fear of being swallowed up by the earth and taken to hell,'' said Paul Greene, an associate professor of psychology at Iona College in New Rochelle, N.Y., who works with disaster victims. "I recall scenes from the movie ‘Ghost' when the evil characters die and their souls are taken down in the ground by demons.''
Sinkholes may not rank as high on the scare scale as hurricanes and tornados, but they hold some allure for popular culture, surfacing as cinematic themes and on apocalyptic websites as a sign of approaching end times.
At the USGS, geologist Randall Orndorff says sinkholes are more common than laymen realize. "They form in fields and woods every day and no one notices except the land owner. Obviously, where property is damaged or a life lost, there's greater awareness. They can be a hazard and we want people to know about them."
In some areas, like Florida, the holes are widely studied and mapped; elsewhere, only those that cause structural damage to a building or road get noted.
"There's no master database of them, but there's no reason to think any more of them are forming," Orndorff said. "There's no sinkhole season."
The USGS hopes to issue later this year the first national interactive map that people can click to see if their property may be in sinkhole country, with links to state resources for more detail, Orndorff said.
The basic ingredients of sinkholes are water -- or sometimes the lack of it -- and soil or rock that's easily eroded underground. Acidic rainwater slowly melts away soft rock such as limestone or salt or dolomite. The removal of groundwater creates voids. Either way, the overlying soil sinks.
Several recent sinkhole deaths have been tied to human activity. Two water-well drillers in Florida died in 2011, when their rigs broke through the roof of a cavern. Also that year, a Bakersfield, Calif., oil worker died in a sinkhole near a well where state officials noted steam had been used for several years to drive crude to the surface.
In Idaho last July, a woman died when she drove her car into a collapsed roadway. Officials later determined that gophers digging nearby had created channels that caused rainwater to undermine the highway.
But it was last month's death of Jeff Bush in his bedroom in a suburban Tampa home that has put sinkholes in the spotlight of media and social media.
"When something like this happens, it seems like it's out of the blue and makes people wonder if they're susceptible,'' said Russell Jones, a psychology professor at Virginia Tech who studies disaster stress. "People need to be aware of the probability of this actually happening to them before they respond in a frightful or arbitrary way."
Recent media reports and Twitter threads in the past two weeks discussed other sinkholes in Florida; Pennsylvania (including one that drained a duck pond) and Louisiana. A memorable collapse on a Waterloo, Ill., golf course swallowed a quarter of a foursome: a 43-year-old mortgage banker who dislocated a shoulder and had to be pulled out by his friends with a makeshift rope.
The Louisiana sinkhole, the 9-acre result of a collapsed salt dome near Bayou Corne that began last year, has displaced about 350 people and drawn a visit from environmental activist Erin Brockovich.
Curiously enough, a 2000 made-for-television movie titled "On Hostile Ground" was also set in Louisiana, with the premise that New Orleans was about to be swallowed by a giant sinkhole on the eve of Mardi Gras.
And a 2003 short film titled "Sinkhole," was shot in part around the mostly abandoned town of Centralia, Pa., which has been smoldering and collapsing from an underground coal fire for more than 50 years.
Yet aside from a few appearances in "Star Wars" films and earthquake flicks and generations of quicksand scenes, the cinematic potential that may lurk beneath our feet remains mostly untapped.
But some observers also see increasing reports of sinkholes as harbingers of greater disasters. They chronicle the events as pointing to the Apocalyse on sites such as :http://endtimesrevelations.wordpress.com/category/sinkholes/
Scripps health and science writer Lee Bowman at BowmanL@shns.com.)