Sinkholes, like the kind that swallowed part of a resort near Disney World in central Florida this week, are more common than you might think.
In the late Sunday night incident, all the guests inside the buildings at the Summer Bay Resort made it out OK before the ground opened up, leaving a 60-foot-wide,15-foot-deep crater.
But sometimes the results have been deadly.
In February, a Florida man fell into a sinkhole that opened suddenly beneath the bedroom of his suburban Tampa home. He didn't survive.
Here is a look at what causes sinkholes, where they occur and just how dangerous and costly they can be:
What causes sinkholes?
Many sinkholes form when acidic rainwater dissolves limestone or similar rock beneath the soil, leaving a large void that collapses when it's no longer able to support the weight of what's above, whether that be an open field, a road or a house. These are called "cover-collapse sinkholes," and it would appear this is what's happening in Florida, where the ground beneath the home suddenly gave way.
Where do they happen?
Sinkholes are particularly common in Florida, which rests on a nearly unbroken bed of limestone, according to the Florida Sinkhole Research Institute.
Central Florida is particularly known for sinkholes. It's part of Florida's so-called Sinkhole Alley, where two-thirds of insurance claims for sinkhole damage occur, according to a report prepared for state lawmakers in 2010. Other places that frequently see sinkholes include Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania, the U.S. Geological Survey says.
Do all sinkholes collapse so dramatically?
No, some merely cause the ground above to sag, or result in small ponds or saltwater marshes, the Florida Department of Environmental Protection says.
How often do they happen?
There do not appear to be any solid numbers, but the Florida Senate Committee on Banking and Insurance reported that insurers had received 24,671 claims for sinkhole damage in that state alone between 2006 and 2010. That's an average of nearly 17 claims a day, just in Florida.
How dangerous and costly are sinkholes?
Deaths and injuries from sinkholes are rare, but certainly not unheard of. For instance, in 2012, a 15-year-old girl died when her family's car fell into a Utah sinkhole, according to media accounts. But the holes are enormously costly. Insurance claims submitted in Florida alone between 2006 and 2010 totaled $1.4 billion, according the Florida Senate report.