TAMPA - Fatalities from sinkholes like the one that opened up in Seffner last week are mercifully rare, but sinkholes in Florida are common. The Tampa Bay area seems to be getting more than it's fair share lately, but experts say the most active sinkhole season lies ahead.
It's all about our geology. Rain water percolating through the ground forms a weak acid that dissolves our porous limestone bedrock. That erosion is happening constantly. But what causes the catastrophic collapse that destroys roads, homes and occasionally, lives?
University of South Florida Geology Professor Mark Stewart says May is the most active month for sinkholes.
"There's an increase in sinkholes in May. That's not so much because of the dryness. It's because we pump more groundwater in May and pumping groundwater is a potential trigger for sinkholes," said Dr. Stewart.
When there's water in the ground and the aquifer water level is high, the surrounding soil holds up. But when that water drains away, the loss of buoyancy can cause the surface to collapse suddenly.
"It's the difference in standing in a swimming pool chest deep in water. When the water drains away you can feel the additional weight on your feet because you've lost that buoyancy," explained Dr. Stewart.
Our current dry spell only makes things worse. And though May is statistically the worst month for sinkholes, we know hard freezes in mid-winter cause strawberry and other farmers to use enormous amounts of ground water to protect their crops. That can trigger sinkholes.
In the freeze of 2010, 140 sinkholes linked to agricultural pumping opened up in the Dover area. A recent count by research group Core Logic showed 15,000 confirmed sinkholes in Florida, most of them in our Central and Northern viewing area.
As we found out from the heartbreak in Seffner, sinkholes are indifferent to the structures and the people that lie above them. And while sinkhole damage claims have gone up steadily, Dr. Stewart doesn't necessarily believe we're getting more sinkholes. It's more likely we're just building more and paving more over very unstable ground.
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