Authorities fear a woman in western Pennsylvania who disappeared while looking for her cat may have been swallowed by a sinkhole — a phenomenon likely caused by mine subsidence.
Search and rescue crews have not seen or heard anything from 64-year-old Elizabeth Pollard since she disappeared on Monday evening, but a sinkhole appeared around the same time about 20 feet (6 meters) from where she parked her car, raising fears that she had fallen into the void. Her granddaughter was found safely inside the car hours later.
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Sinkholes are not always associated with mining. In 2013, a man was killed when a sinkhole opened up beneath his home in central Florida, where the porous limestone base gives rise to thousands of sinkholes every year.
The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania. Fatalities are rare.
What are sinkholes?
A sinkhole is an area of ground that has no natural external surface drainage and can form when the ground below the land surface can no longer support the land above, according to the U.S. Geological Survey.
The land usually stays intact for a period of time until the underground spaces just get too big. If there is not enough support for the land above the spaces, then a sudden, dramatic collapse of the land surface can happen.
How common are sinkholes?
Sinkholes are most common in what geologists call karst terrain, which involves types of rock including limestone below the land surface that can naturally be dissolved by groundwater circulating through them. They can also happen due to old underground mines.
Florida is highly susceptible to sinkholes because it sits above limestone.
How big are sinkholes?
Sinkholes can range in size from just a few feet wide to ones that cover a vast area spanning hundreds of acres. The hole that may have swallowed Pollard was just the size of a manhole cover when it was discovered early Tuesday.
Their depth can also vary from just a few inches to more than 100 feet (30 meters). Some are shaped like shallow bowls or saucers, whereas others have vertical walls. Some hold water and form ponds.
What caused the sinkhole in Pennsylvania?
The sinkhole in the Unity Township community of Marguerite, where search and rescue crews still hope they could find Pollard alive, appeared above the site of the Marguerite Mine, which was last operated by the H.C. Frick Coke Company in 1952.
The Pittsburgh coal seam is about 20 feet (6 meters) below the surface in that area.
Underground coal mining has taken place in 29 of the 67 counties in Pennsylvania, and a wide swath of the state’s southwestern region is at risk for soil subsidence, where underground materials shift or fall into voids created by mining and other extraction of mineral resources.
Department of Environmental Protection spokesperson Neil Shader said the state’s Bureau of Abandoned Mine Reclamation will examine the scene after the search is over to see if the sinkhole was caused by mine subsidence.
Other recent sinkholes
In June, a giant sinkhole in southern Illinois swallowed the center of a soccer field built on top of a limestone mine, taking down a large light pole and leaving a gaping chasm where squads of kids often play. No one was hurt.
In 2023, the sinkhole that in 2013 fatally swallowed 37-year-old Jeff Bush in suburban Tampa, Florida, reopened for a third time, but it was behind chain-link fencing and caused no harm to people or property. Officials said the sinkhole reopening was not unusual, especially in central Florida with its porous limestone base. Bush's body was never recovered.
A large sinkhole opened up in 2020 in South Dakota near where a man was mowing his lawn. Testing revealed a large, improperly sealed mine beneath part of the housing subdivision, and a 40-foot-deep (12-meter-deep) pit mine in another corner of the neighborhood, a lawyer for some of the area homeowners said. Since the first giant collapse, more sinkholes have appeared.
A large sinkhole that swallowed oil field equipment and some vehicles in southeastern Texas in 2008 expanded in 2023 when another sinkhole developed and joined the first one.