An anonymous reader writes "Last Thursday night, a sinkhole took the life of a man (TV news video, with ad) while he slept in his home in Seffner FL, near Tampa. While human fatalies are rare, sinkholes are so common in Florida that the insurance industry successfully lobbied the state lawmakers to pass legislation in 2011 making it more difficult for homeowners to claim sinkhole damages. The bedrock in Florida is limestone, a weakly soluble mineral formed from calcified deposits of sea creatures tens of millions of years ago. Above the limestone is a clay layer called the Hawthorn Formation which shields the limestone from ground water; and above the clay is sand. However, the protective clay layer is thin or nonexistent in some areas of Florida, particularly in the middle part of the state near the Gulf coast, where caves and sinkholes are common. Geologists say that human activity, particularly construction and irrigation, can trigger sinkholes by destabilizing the landscape above caverns by drawing down water tables and massing structures above them."