Giant sinkholes like the one that swallowed a Florida man this week aren't so rare as you might think—and are sometimes caused by human behavior, the Christian Science Monitor reports. About 15,000 exist throughout Florida, most of them appearing slowly over a period of years while groundwater erodes the limestone bedrock above an underground cavern. Occasionally a catastrophic sinkhole suddenly appears and takes someone with it; the state has three sinkhole fatalities on record.
Damage from sinkholes has grown so costly for Florida insurance companies that they successfully lobbied for a new law, making it more difficult to claim sinkhole damages. The scary part: People sometimes create their own sinkholes with construction work (like well-drilling) and agricultural irrigation. How to spot one coming? Geologist Anthony Randazzo tells NPR that there are tell-tale signs, like "you begin to develop cracks in masonry structures." But with catastrophic sinkholes, look for "cracking and ground-tilting or floor-tilting, doors won't open or will get stuck, windows will not be able to open properly." Click for more on the latest sinkhole.