Why do so many more sinkholes open up after a hurricane?
Monday, June 18, 2018
The front page story in our local newspaper, The Villages Daily Sun, right after Hurricane Irma was about all the sinkholes that suddenly appeared around the area. While it is always surprising when a sinkhole abruptly collapses, storms are known to activate them for several reasons:
•• The normal development of sinkholes involves pockets of acidic water slowly dissolving the limestone karst that underlays the soil in most of Florida. Heavy rain and flooding during a hurricane speeds up the process, and organic debris in the water increases its acidity.
•• The individual soil particles lose their natural ability to adhere to each other when they become saturated after heavy rain, and standing water adds weight over a sinkhole void underground, making it more likely to collapse.
•• Smaller solution sinkholes, called “chimney sinkholes,” are also more likely to appear after a hurricane. We noticed a new one, shown below, at a golf course near us the week after Irma.
They look like a tortoise or armadillo hole at first glance but, on closer examination, part of the opening will extend straight down and some are big enough for a child to fall into.
•• A hurricane that follows a period of drought is especially likely to cause sinkholes. Drought lowers the water table and creates pockets of air in the void spaces of the underlying karst that once were filled with water; then the heavy hurricane rains weigh down the soil above it. With the buoyancy that the water is the karst pockets once provided now gone, collapse is more likely to occur.
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