A Deadly Sinkhole

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Bob Bonwit, a hospital nurse, came home from work in his scrubs, headed out the back door to feed his two horses some carrots, and realized immediately and to his horror that something was very wrong. His night vision still adjusting, Bonwit gasped and recoiled when he saw that his barn was sinking into the ground and with it, his two cherished equine friends, 17-year-old Jack and 13-year-old Magic, both Tennessee Walking Horses. A 30-foot-deep by 50-foot-wide sinkhole was the culprit, and in spite of the combined efforts of geologists, veterinarians, fire and rescue workers armed with the latest technology and technique, both horses perished in Sanford, Florida, a suburb of Orlando.

Too Much…Not Enough

Alan Harris of Seminole County EMS/Fire/Rescue said, “the hole started to form on the outside and moved towards the barn, opening up underneath. Here in Florida, these air pockets are common, and can be aggravated by either too much or not enough rain, for example.”

When workers arrived shortly after midnight, November 15, they found Magic standing on Jack’s body. Harris describes the scene: “It was the worst situation the horse could have been in, and I was shocked that he was still alive. He’d fallen 30 feet, a tree had landed on him, and the barn was on its side, water rushing in all the while.”

Groundwater had almost completely covered the horse’s body, leaving only his nose exposed. Pumps did their job by keeping most of the water at bay, and a carefully maneuvered crane did manage to lift Magic out, but compartmentalization probably killed him, surmises Harris, who’s seen the phenomenon take human life. “That’s when pressure is finally relieved on the internal organs—after being held in place—and they ‘bleed out,’ causing death.”

Harris confirms that, even with the help of a tow truck, the crane and a pulley, plus expert supervision, the trauma was just too much for the horse. “Everything that could possibly be done was done to try and save Magic,” he laments.

The sinkhole continued its widening grasp for several days, finally stopping a few feet short of Bonwit’s house.

Think “Underground Caves”

Dr. Shiou-San Kuo, of the Florida Sinkhole Research Institute and a professor of civil and environmental engineering at the University of Central Florida, elaborates: “Due to our geological foundation in Florida, limestone bedding can vary from deep to shallow and weak to strong. Underground cavities appear to be almost everywhere in Central Florida.”

But sinkholes are also quite common in Pennsylvania and Kentucky: think “underground caves,” suggests the geo-technical expert.

Weak sections in the limestone are a critical factor in the formation of sinkholes. In Florida, these pits in the earth develop relatively slowly and usually give people a chance to get out of their way until they stabilize on their own or are filled with grout, according to Dr. Kuo. More sinkholes, he says, are seen when it’s very dry or very wet, between April and October in the Sunshine State.

He estimates the appearance of a total of approximately 3,000 sinkholes in the past 30 years. “It’s really a very small percentage,” figures Kuo, who adds that some sinkholes can literally take hundreds of thousands of years to form.

What to Do?

What’s a cautious barn builder to do? If you’re in a sinkhole-prone area, call your closest college or university and ask for the departments of engineering or geology. A member of the faculty may be able to advise you or recommend you to a professional who can assist. Reputable construction or civil engineering companies may also be a good resource.

Kuo notes that observation can play a role in predicting sinkholes, especially if, amid healthy vegetation, you notice an area where nothing seems to be growing. The more aggressive “boring test” drills steel pipe into the ground. “If a cavity exists beyond 50 feet, it probably would not cause any damage to surface structures,” postulates Kuo.

Sinkholes routinely wreak havoc in Florida, reports fire department spokesperson Harris, who is used to seeing holes generally in the range of five to ten feet wide. “Usually, they can just be filled with sand,” he says.

Twenty-one years ago, the largest sinkhole in modern Central Florida history swallowed a tree as a bewildered homeowner looked on. Before it was finished, the Great Winter Park Sinkhole had consumed her home, a luxury car dealership and a city swimming pool. It then filled with water, leaving a new lake 350 feet across.