The disappearance and presumed death of a Florida man late last week through a sinkhole that opened up in his bedroom seemed the epitome of an unforeseeable tragedy.
But that's likely not quite true, local geologists and engineers say.
The hole truth• A sinkhole is an area of ground that has no natural external surface drainage -- when it rains, all of the water stays inside.
• Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds or rocks that can naturally be dissolved by ground water circulating through them.
• The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania.
• Sinkholes can vary from a few feet to hundreds of acres across and from less than 1 foot to more than 100 feet deep. Some are shaped like shallow bowls or saucers; others have vertical walls.
• New sinkholes have been correlated to land-use practices, especially from groundwater pumping and from construction and development practices. Sinkholes also can form when natural water drainage patterns are changed and new water-diversion systems are developed.
Source: U.S. Geological Survey
And while sinkholes do occur in the Chicago suburbs, experts agree they aren't likely to happen as severely, or for the same reasons, as the one that claimed the life of Floridian Jeff Bush.
While Florida sits atop a weak type of limestone that dissolves easily in an active water table, the Chicago area has among the most solid ground there is, said Bill Prigge, principal of Midland Standard Engineering and Testing in East Dundee.
"The bedrock in this part of Illinois is particularly strong," Prigge said. "It's called dolomite limestone."
Sinkholes that have occurred in the Chicago suburbs are most often caused by water main breaks, though natural springs -- of the kind that exist in the East Dundee area -- also are potential factors, he said.
Whenever water moves below the ground, it also moves what's around it -- eventually affecting what's above it as well, East Dundee Village Administrator Bob Skurla said.
Last September, a sinkhole began to open in the parking lot of Dundee Automotive at Route 72 and near Route 68, causing some damage to the pawnshop next door as well.
A decade earlier, a 10-by-15-foot area of the parking lot outside Dundee Manor restaurant sank as much as 7 feet into the ground, causing three vehicles to fall in.
Though a water main break was the first thing suspected in both cases, the proximity of the natural springs that supply D'Angelo Natural Spring Water in the village also has come into consideration, Skurla and Prigge said.
A 15-by 20-foot sinkhole that opened in July 2011 at the intersection of Dundee and Hicks roads in Palatine was determined to have been caused by a collapsed sewer after a major summer rainstorm.
"Because of age and corrosive gases, the sewer crown deteriorated over time," said Allison Fore, spokeswoman for the Metropolitan Water Reclamation District of Greater Chicago. "The heavy rain contributed to acceleration of the sinkhole's development and subsequent enlargement."
As far as last week's tragedy in Florida, what was immediately obvious to C. Pius Weibel, senior geologist of the Illinois State Geological Survey, was that the victim's house was built on a site it shouldn't have been.
"Certainly he was in the worst spot," Weibel said.
Though residents of that area should have known they were in an area prone to sinkholes, Weibel speculates that no ground survey was ever done before construction began on the house, likely decades ago. An in-depth and costly study would be needed to determine whether the houses near Bush's face a similar threat.
Even in areas where conditions are favorable for sinkholes, they could occur clustered together or spread out, Weibel said.
Florida is among the states most prone to sinkholes -- certainly more prone than most areas of Illinois. Weibel and Prigge agreed that southern Illinois is the part of the state most likely to see sinkholes caused for the same reasons as in Florida.
"Wherever there's caves, there's potential for sinkholes," Prigge said.
He added that the complete collapse that happened last week is usually preceded by some warning of structural damage -- like cracked walls or the inability to close windows -- that allows some time for preventive measures to be taken.