CLARKSVILLE, Tenn. – Sinkholes are nothing new to the Clarksville-Montgomery County area, and many have been discovered in recent years.
Dr. Phillip Kemmerly, Professor Emeritus of Geology at APSU and Licensed Professional Geologist in the states of Kentucky and Tennessee shared his professional knowledge regarding these hazardous holes. Kemmerly has worked in the field of geology for over 40 years, 39 of which he spent at APSU.
Sinkholes develop in rocks that are soluble by slightly acidic water, particularly the limestone deposits found throughout the city of Clarksville. When groundwater moves through fractures and cavities in the rock, it is flushed back upward, causing the soil above to fall in, creating the sinkholes seen on roads and in yards.
Kemmerly said the Clarksville area, which compromises the southernmost tip of the Mammoth Cave zone, is the second-most well-known karst topography in the world, meaning the land beneath is a prime spot for sinkhole development.
“In an urban area like Clarksville that’s rapidly growing, there’s increasingly more surface covered by roadways and parking lots, which typically causes multiple occurrences,” Kemmerly said. “The changes required to build a city over this kind of terrain tend to aggravate the problem.”
He said certain areas of the city, particularly near St. Bethlehem, Sango, and Exit 11, are more prone to these problems, but no area is considered risk-free.
Detection of sinkholes is no easy task. Experts use electrical currents to find at-risk areas before some commercial buildings are constructed, but the measure is not cost-effective and is not typically used for residential areas. Kemmerly suggested potential home buyers and builders request to see a preliminary ‘plat map’, which provides a contoured view of the lot. Smaller elliptical or circular patterns often indicate karst terrain.
Homeowners should also seek professional assistance if they notice small holes forming in their yards, which may be no bigger than a saucer or coffee cup, according to Kemmerly. Curves or cracks in the soil and yellow patches of grass adjacent to green patches are also potential warning signs.
Kemmerly said geologists generally do not believe it is best to fill a sinkhole once it develops.
“My advice whenever possible is just to avoid getting anything very close to it in the way of structures. But that’s rarely done around the country where we have this kind of terrain,” he said.
His best suggestion for filling the holes is to use shot rock (limestone), and cover the area with clay after it is packed down. This is not always a permanent solution, but Kemmerly said it is the most effective.
“Each one of these (holes) has its own set of characteristics. They have general features that are alike, but each one is an individual, which makes it very difficult to make a blanket judgment about any given site without examination and evaluation.”