Sinkholes, a worldwide hazard that lurks wherever limestone bedrock is found, are investigated.
In Tampa, Florida, in February 2013, a giant hole in the ground opened up and swallowed half a house, killing 36 year-old Jeffrey Bush as he slept in his bedroom. A month later, a golfer in Illinois survived an 18-foot fall when the 14th hole caved in beneath his feet. Both were victims of sinkholes-a notorious worldwide hazard that lurks wherever limestone bedrock is found. When carbon dioxide dissolves in rainwater, it forms a weak acid that attacks the soft limestone, riddling it like Swiss cheese with hidden underground rivers, caves and hollows. While this process of erosion takes millions of years, the fragile roof of a cavern near the surface can collapse in an eye blink, with little or no advance warning. Sinkholes can range from a few meters across to one in Egypt that measures 50 x 75 miles, and a Chinese hole nearly half a mile deep. Filled with compelling eyewitness video of collapsing sinkholes and authoritative science from expert geologists, NOVA investigates what it's like to have your world vanish beneath your feet.