A couple of weeks ago I was at a conference dedicated to sinkholes held in St. Louis. About 100 engineers and geoscientists from a total of 14 or 15 countries gathered to discuss issues related to sinkholes in various geologic settings, but primarily limestone karst.
Heres a link to the conference program, and a proceedings will be published later this year. There were a number of interesting presentations, the most interesting of which (to me) was about the giant cylindrical sinkhole that developed in Guatemala City last year during a tropical storm. The speaker explained that the sinkhole was caused by failure of a deep storm water tunnel system, not by the tropical storm. Unlike sinkholes in Illinois, this one formed in pumice, volcanic rock. Check it out:
Prior to the conference, Sam Panno of the Illinois State Geological Survey, Illinois Mr. Karst, led a field trip into the Sinkhole Plain of Illinois, just across the Mississippi River and south of St. Louis. [If you want to know anything about karst in Illinois, go to the ISGS Publications webpage and search on Panno.] Despite the chilly weather and about an inch of new snow on the ground, the trip was a great success. We stopped at several springs and cave openings, although we couldnt enter any caves because they have all been closed to human traffic in hopes of preventing the spread of white nose syndrome, which is killing massive numbers of bats in the Eastern U.S. The prettiest stop was at Falling Springs, near Dupo, IL. The spring exits a cave midway up a 150-foot limestone bluff. As the water falls and hits the ground, carbon dioxide is released causing a calcium carbonate rock known as tufa to precipitate. We estimated that the tufa is growing about an inch a year from the bluff face.
At one of the stops, I talked about spring water quality in the Sinkhole Plain. Its not good, although it has improved somewhat in the last 10-15 years. The main problem is spring water is typically loaded with bacteria, usually including fecal bacteria such as E. coli and Enterococcus. Chemical contaminants include pesticides and nitrate.Below isa graph showing fecal coliform counts (which is related to E. coli) for about 10 springs we sampled 6 times in 1998-2000. Keep in mind that for drinking water purposes, the concentration needs to be zero. The bacteria are coming from septic systems and livestock manure. In this region, where there are many large sinkholes and caves, water travels from the land surface to the water table extremely quickly with little time for processes to retard the movement of contaminants. Thus groundwater is very vulnerable to surface-derived contamination, and extra care must be taken to avoid pollution.
I always get a kick out of the Jack Daniels ads that talk about their pure limestone spring water. [Note: must be 21 to visit the Jack Daniels site.] If their spring water is anything like we see in Illinois, and the geologic setting is pretty similar, then its hardly pure. I assume the fermenting process takes care of those fecal bacteria!
