HUSAR: Sinkholes not unusual, falling into one is

Posted: Mar. 14, 2013 9:31 pm Updated: Jun. 6, 2013 11:15 pm


When sinkholes hit the national news, Sam Panno's phone starts to ring.

When sinkholes make news twice in little more than a week -- once when a sinkhole swallowed a Florida man and his bedroom Feb. 28 and twice when a golfer fell into a sinkhole on the 14th fairway at Annbriar Golf Club in southern Illinois last week -- Panno stays even busier than usual.

"Bottom line, it's a very rare occurrence. It just happened to occur here in the U.S. on almost the same week," Panno, a senior geochemist with the Illinois State Geological Survey, said in, naturally, a phone interview with The Herald-Whig.

Falling into a sinkhole wouldn't be a concern for Panno even in Adams, Brown and Pike counties, which have the karst landscape typically pockmarked with sinkholes.

"In Illinois, the sinkholes aren't as big as the ones in Florida. They don't swallow the house and all the occupants," Panno said. "They actually do damage to the foundation, very much like mine subsidence. That would be a more realistic concern."

Another concern with Illinois sinkholes is they act as "recharge points" that allow surface-borne contaminants into groundwater without first going through the soil.

"You can get contamination of these aquifers very easily," Panno said.

Sinkholes are naturally occurring, forming as soil collapses into a crevice and is carried away through a conduit by water, according to the State Geological Survey's website. What happens next is the soil roof of the developing sinkhole falls into the hole to form a cylindrical cavity, then more soil cover collapse causes circular cracks to develop at the surface and erosion by water flowing into the new drain hole forms the typical inverted cone- or bowl-shaped depression.

They're most common in areas with less than 50 feet of sediment sitting on top of the bedrock and with lots of caves. Adams County has caves and sinkholes in the southwestern part of the county, but sinkholes are more common in other areas of the state, particularly in St. Clair, Monroe and Randolph counties southeast of St. Louis, which have about 15,000.

The golf course sinkhole occurred in Monroe County, which has 30 feet of soil over the bedrock that can collapse into the creviced limestone underneath to form a dome-shaped structure maybe 10 feet in diameter, Panno said. Groundwater washes away sediment at the bottom of the structure, so more soil can collapse into it, as the sinkhole works its way to the surface.

On the golf course, "grass was all that was left of the soil under that guy, and it broke through like a cheap carpet," Panno said. "Not many people have the opportunity to see the inside of a sinkhole like that, but it was extremely dangerous, too. When you get that type of feature, it tends to continue to collapse."

Panno said he wouldn't be concerned about sinkholes unless he was surrounded by them -- or buying property with sinkholes.

"If you have a well, water quality would be foremost. Next would be foundation problems. Way down there is actually falling into one that's actually forming," Panno said.

Most sinkhole incidents actually go unreported.

"The problem is, people that have problems with their foundations don't report them in general. If somebody has a sinkhole forming under their house, they usually fill it in. If it happens again, they fill it in and sell the house," Panno said.

"It's like having sewer problems or flooding problems in your house -- you don't advertise it if you want to sell your house. That's the problem. We just don't know how many people are having problems. There's no way to know."