Monroe County sinkholes: Should residents be afraid?

by Michael Mosher on June 13, 2013

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Many Monroe County residents could be living on a sinkhole and not know it.

Sinkholes in the county are nothing unusual. In fact, they’re quite common, according to C. Pius Weibel, senior geologist with the Illinois Geological Survey.

“There are probably more sinkholes in Monroe County than any other county in Illinois,” Weibel said.

Although a man fell into a sinkhole last month at Annbriar Golf Course near Waterloo, the known sinkholes — about 13,000 — are not the primary concern of the county’s residents, professional geologist Philip Moss said. The documented sinkholes are visible as depressions in the ground, but there are an unknown number of hidden sinkholes that can only be definitively identified through geophysical surveys.

The primary area of concern is within the sinkhole plain in the western part of the county. Moss said that, to his knowledge, there has been no effort made to map these hidden sinkholes, which could number in the tens of thousands.

“The tests would be expensive and labor intensive,” Moss said. “If someone has a particular interest, they need to have a survey done on the property they are interested in.”

Commercial developers should consider paying for a geophysical survey before construction, Moss said. Private homeowners should be careful about where they choose to build.

“Within the sinkhole plain, flat spots are very suspicious to me,” Moss said. “If I were a homeowner, I wouldn’t build on flat land.”

The land given preferential treatment for development in Monroe County is the least productive farmland, which is hilly, he said. The land with the most hills contains the most sinkholes. It’s Moss’ contention that the flat areas between the hills are most likely to have hidden sinkholes, which, like visible sinkholes, formed over thousands of years as holes that formed in the soil and migrated toward the surface.

More land is being developed as the county’s population continues to grow. The census bureau estimated that 33,357 people lived in Monroe County in 2012, a 21 percent increase since 2000. The county experienced a 23.2 percent growth rate between 1990 and 2000.

Hidden problem

A dilemma for those who live in the sinkhole plain is that they probably do not know they live in a problem area. Much of western Monroe County and a portion of southern St. Clair County are in the plain. Although the sinkhole plain has been well-documented, its exact location is very difficult for the average citizen to determine.

Moss said neither the Monroe County Geographic Information System website ( nor the Illinois Department of Natural Resources website make the information easily available to the public. The Illinois DNR website has maps that identify the sinkhole plain, but Moss said the maps are too encompassing and include areas not in the sinkhole plain.

The Monroe County Comprehensive Plan maps all known sinkholes in the county, but does not indicate what land is in the sinkhole plain. Property owners or perspective buyers can buy special software to view sinkhole plain maps, or contact an engineering company that may be willing to share the information.

Monroe County Zoning Administrator Mike Fausz said that a soil and water report must be completed on all land being developed. The report will tell whether the land has “karst” characteristics.

Karst is a landscape formed by the process of soluble (dissolvable) rocks being broken down under the ground. About 9 percent of Illinois and 33 percent of Monroe County is karst, which is characterized by sinkholes, caves and underground drainage systems.

A potential developer may not know what karst is, but they have a duty to educate themselves, Fausz said.

“Can I tell you that everyone knows what karst is? No. But if someone is going to do development, they will need to do their due diligence,” Fausz said.

The Monroe County zoning code has regulations for developing on known sinkholes and restricts mobile home parks from being built on karst topography. There are no codes for other types of development on karst, Fausz said.

Is more regulation needed?

Moss, who is a karst expert, believes the regulations for building on karst should differ from those for building on all other landscape types. Weibel said there was a push about 10 years ago to have statewide rules for karst development, but they were never enacted. He agreed with Moss that regulations are needed.

“There should be some rules in those areas to protect their own people, because it really is different,” Weibel said.

Moss believes that residents of the Illinois Sinkhole Plain should be more concerned with their fiscal safety than their physical safety. Because houses are typically larger than sinkholes, a home on top of a hidden sinkhole isn’t likely a safety concern.

“Generally there is enough structural integrity that it would cause a lot of damage, but not death,” Moss said. “But, the damage could be greater than the value of the home.”

Homeowners are at risk because their insurance policies do not protect them in the case of sinkhole damage. Insurance broker Joe Swierczek, of FLS Insurance Agency in Columbia, said sinkhole insurance is a separate part of policies, and one not many people have chosen.

“After the Annbriar incident, a lot of clients called to check to see if we have it,” Swierczek said. “We added it to a handful of policies.”

Few companies offer sinkhole insurance in Illinois. Connie Fingerhut, of FLS Insurance Agency, said only two of the 10 companies the agency works with offer the coverage, which is different than mine subsidence and earthquake insurance.

It would cost less for a person living in the sinkhole plain to buy sinkhole insurance than to have their land surveyed to determine whether their home is in danger, Moss said. Fingerhut estimated that most homeowners can purchase the insurance for less than $100 per year, although the cost varies based on the price and type of home.

Moss suggested that if a person decides against buying insurance, their other options are to sell or hope no sinkhole damage will occur. He acknowledges that he does not know of any cases in Monroe County in which a home was proven to have suffered sinkhole damage.

Should residents be afraid?

Although he is unaware of any homes damaged from sinkholes, Moss thinks the growing population of Monroe County, coupled with the lack of information about the potential hazard, make it likely that an incident will occur in the future.

Climatologist Iben Browning predicted a major earthquake would occur on Dec. 3, 1990, in the New Madrid Seismic Zone, located in southeastern Missouri, northeastern Arkansas, western Tennessee, western Kentucky and southern Illinois. The day passed without so much as a tremor, but Browning’s prediction raised awareness that a major earthquake could occur in the region.

About 50 percent of FLS’ clients carried earthquake insurance prior to Browning’s predictions. After the prediction, about 99 percent picked it up and have kept it, Swierczek said.

Moss is not predicting imminent disaster or expecting a Browning-like response for sinkhole insurance, he just wants the public to be aware of potential risks.

“I’m not trying to protect people from themselves,” Moss said. “I’m trying to protect people from a lack of information, people thinking they have insurance and they don’t.”

Moss said he did not want to alarm anyone living in the sinkhole plain.

“I don’t want to panic people that if they own a house in the sinkhole plain that it’s a matter of time until it sinks. I don’t think that is true at all,” Moss said. “(A sinkhole) could open up at any time, but it is unlikely to be life-threatening. It could be financial solvency threatening.”

Full article…here


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