TORONTO – The presumed death of a Florida man who disappeared as a sinkhole opened under the bedroom of a house has people wondering how much of a risk such holes could be.
Sinkholes are common in seaside Florida, whose underlying limestone and dolomite can be worn away by water and chemicals, then collapse.
According to the Florida Geological Survey (FGS), “acidic ground water slowly dissolves cavities and caves in the limestone over a period of many years.”
“When the cavity enlarges to the point that its ceiling can no longer support the weight of overlying sediments, the earth collapses into the cavity,” explains the FGS website.
So what are some warning signs? Florida’s Lake County engineering department provides a list:
• Fresh exposures on fence posts, foundations or trees caused by the ground sinking
• Slumping, sagging or slanting fence posts, trees or other objects
• Doors and windows that stop closing properly
• Small ponds of rainfall where water hadn’t collected before
• Wilting of small, circular areas of vegetation
• Cloudy water instead of clear water pumped from nearby wells
• Cracks in walls, floors, pavement and the ground surface that’s different from a few hairline cracks normally seen between concrete blocks
But there may not always be warning signs.
Pierre Robin, a geology professor at the University of Toronto, says you cannot always predict when the ground will collapse.
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“The rock under the ground has to be soluble, and the water has to be available to dissolve it and take it away in solution,” he told Global News. “It’s a small hole that progressively becomes a big hole….it occurs over thousands, tens of thousands, millions of years.”
So how can you fix a sinkhole?
If it’s a small hole, the FGS says to fill it with clean sand or soil. The FGS says not to use waste or anything that could potentially release toxins into the groundwater.
If the sinkhole is larger, broken limestone or a concrete plug in the bottom of the sinkhole is suggested to help create a foundation for the fill. Then add clayey sand to prevent water from seeping down and top it off with sand and top soil, says the FGS.
“Additional fill may be necessary over time, but most holes eventually stabilize,” reads their website.
With a file from The Associated Press
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