How dangerous are sinkholes? What to know amid search for missing Pa. woman
Pennsylvania − where a search has been launched for a missing grandmother who may have fallen into a sinkhole − is one of the states where the holes are most likely in the U.S.
Officials have been looking for two days for Elizabeth Pollard, 64, who disappeared while she was looking for her cat. Her car and her 5-year-old granddaughter were found safe near a restaurant in Unity Township, about 40 miles southeast of Pittsburgh.
Officials also found a sinkhole about the size of a manhole cover, and when they sent a camera down into it, they discovered what looked like a shoe inside.
Here's what to know about sinkholes in the U.S.:
What is a sinkhole?
A sinkhole is a hole in the ground that opens up when there is no external surface drainage. When water builds up, it drains into the subsurface and dissolves the sediment below, creating caverns until the ground surface itself collapses, according to the U.S. Geological Survey.
Sinkholes can form because of natural or manmade causes, according to Pennsylvania's Department of Environmental Protection. They also can crop up after extreme weather such as hurricanes.
Sinkholes can range in size from a few feet wide to hundreds of acres, and anywhere from 1 to 100 feet or more deep. Sinkholes can swallow up cars, parts of roads and even houses.
There's no national database that tracks sinkholes, but the U.S. Geological Survey conservatively estimates that they have cost on average $300 million per year in damage over the last 15 years.
Where are sinkholes most common in the US?
Florida, Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania are the U.S. states where sinkholes are most likely to open up, according to the American Geosciences Institute.
They're most common in karst terrain, where the kind of rock under the surface can become dissolved by groundwater, such as salt beds and domes, gypsum or limestone, according to U.S. Geological Survey. Florida's terrain is largely limestone under the surface.
Three counties in Florida's Tampa area make up a region sometimes called "sinkhole alley" because of the over 20,000 sinkholes there, almost 75% of the sinkholes in the whole state, according to the Sarasota Herald-Tribune, part of the Paste BN Network.
One small U.S. town is known for having more sinkholes than it does people: In Fountain, Minnesota, there are only about 400 residents and 10,000 sinkholes, KARE reported.
Sinkhole accidents in US history
Alabama claims to have had the largest relatively recent sinkhole collapse in the country, according to the USGS. The so-called "Golly Hole" in Shelby County suddenly opened in 1972 and measures 325 feet long, 300 feet wide and 120 feet deep.
In 2013, a Florida man was killed as he slept when a sinkhole near Tampa opened up. His brother jumped in to save him but had to be rescued, and five other people escaped unharmed. That same sinkhole reopened for a third time last year, and was 19 feet wide at its largest point.
Earlier this year, a Kentucky man was working in a field during rain when he fell about 30 feet down into a sinkhole in Warren County, WBKO News reported. Responders were able to rescue him after he was trapped for about an hour and he was treated for minor injuries at a hospital.
Also this year, a giant sinkhole swallowed the center of a soccer field in Alton, Illinois. There were no reports of injuries. Video caught the green turf as it randomly caved in, sucking a stadium light pole down with it and sending up a gray cloud.
Contributing: Natalie Neysa Alund, Taylor Ardrey and Camille Fine, Paste BN