It's a sinking feeling (Huntsville, Alabama)

Published November 18, 2007
Experts say the severe lack of rainfall has increased the risk of sinkholes, like the one that damaged an expensive home in Madison's Cambridge at Heritage Plantation neighborhood last week.

Although the problem in Madison has not been linked to the drought - city officials say it could just be soft soils and normal settling - dry times tend to be prime time for sinkholes, said Dr. Scott Brande, a geologist and associate professor at the University of Alabama at Birmingham.

Rainfall keeps North Alabama's many underground limestone caves flush with water, which Brande said acts as a "load bearing material" to help support the weight of the soil and rocks above the caves. During droughts, he said, cave water levels tend to drop. If it drops enough to make the earth above collapse, a sinkhole is born.

The Huntsville area has always been a hotbed for sinkholes because it is pocked with underground caverns. Blame it on our bedrock: the Rocket City sits atop a massive limestone outcrop that Brande said was formed 450 million to 500 million years ago. The main ingredient of limestone is calcite, a mineral that is easily dissolved by the mild acids in rainwater.

Acids eat away the calcite, creating voids in the limestone. After a few hundred years of rain seeping into bedrock, a small void can grow into a large underground cave that can become a sinkhole.
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