The Unity sinkhole investigators suspect a woman fell into late Monday could be the result of an abandoned mine, according to the state Department of Environmental Protection.
The DEP’s Bureau of Mine Safety was dispatched to Unity’s Marguerite Road early Tuesday. Upon initial review, officials suspect the sinkhole was caused by the abandoned Marguerite Mine, which was last operated by H.C. Frick Coke Co. in 1952, said spokesperson Lauren Camarda.
Elizabeth Pollard, 64, was reported missing by family members Monday night after she left home to search for her cat. Investigators suspect she fell in a sinkhole along Marguerite Road.
It’s about 20 feet from the surface down to the coal seam, Camarda said. The DEP’s Bureau of Abandoned Mine Reclamation will investigate the site further to determine whether the sinkhole was caused by mine subsidence once police and first responders have cleared the scene.
Underground coal mining has taken place in 29 of the state’s 67 counties, including much of Southwestern Pennsylvania, Camarda said.
“Each year, (the) DEP works to address historic abandoned mine land features across the commonwealth with available federal funding and address emergencies as they arise,” she said.
Although mine subsidence is the first suspect in most sinkholes, geologist Craig Clemmens said there are other possible causes.
“Most sinkholes develop naturally,” said Clemmens, who has worked about five decades as a geologist. “There are some formations that can be dissolved by water, particularly limestone — you get water running through the cracks in the ground and it slowly dissolves the minerals out as it goes.”
This is the process that formed Fayette County’s Laurel Caverns, said Clemmens, who now works part time after retiring five years ago from Appalachian Geophysical Surveys in Westmoreland County’s Washington Township.
Artificial sinkholes, however, form when an underground mine collapses, a dam leaks or a water main line breaks, he said.
Clemmens suspects the Unity sinkhole is an artificial one.
Sinkholes are not common in Southwestern Pennsylvania, he said.
“They are a pretty rare occurrence, but they do happen. You open a cavity underground, and it’s eventually going to close back in,” Clemmens said. “You go down to Florida where it’s mostly limestone, aragonite geology in the bedrock, there are frequently problems with sinkholes. Sometimes a sinkhole will eat an entire house.”
Westmoreland County’s geology mostly consists of shale and sandstone, Clemmens said. Although there are some thin beds of limestone in the region, they are unlikely to cause sinkholes, he said.
Clemmens recommends all Southwestern Pennsylvania residents look up their address in Penn State’s online mine map atlas to see if their property sits above abandoned mines.
The maps are not foolproof, Clemmens said.
“We know from the Quecreek story that they’re not always accurate mine maps,” he said. “One thing that happened years ago is that people would open a mine here and it would show that they’ve mined out this area. But they would go next door and steal the coal from out under their neighbor’s property and not report it.”
Nine miners became trapped in Somerset County’s Quecreek Mine in 2002 when, relying on outdated maps, they mistakenly bored through an abandoned section of a neighboring coal seam.
Mine subsidence insurance, Clemmens said, is a fairly cheap way for residents to protect their homes in the case of a sinkhole. All abandoned mines, he said, collapse eventually.
“It might take a thousand years,” Clemmens said. “But that subsidence insurance is available.”