It's a nightmare scenario; you're at home—maybe even sound asleep in your bed—or perhaps just walking down the street, and all of a sudden, the ground beneath you literally opens up, swallowing homes, cars, trees and even people into a muddy, seemingly bottomless pit. If you're in California, you might attribute such a catastrophe to an earthquake, but in Florida, chances are you've just witnessed—or been the victim of—a sinkhole. Some regions of the country are prone to sinkholes because of their geologic makeup, including some parts of New Jersey.
The Hole Story
The first thing you need to know about sinkholes is that there are two different kinds. The one where the ground opens up and houses fall in, like in a horror movie? That’s called a cover collapse sinkhole, and they are—thankfully—relatively rare. “Large scale sinkholes are very rare in the Northeast,” says Thomas Roman, owner and president of Quality 1st Contracting in Cliffwood. “I’m not familiar with any here in New Jersey that have swallowed up anything. It’s been over 25 years since we’ve seen anything like that.”
The other—and by far more common—type is a subsidence sinkhole. This is when water gradually erodes the layer of sedimentary rock below the surface. The most famous example is the sinkhole beneath the Leaning Tower of Pisa, which modern Italian engineers have managed to arrest…but not arrest so much that the wonder of the world loses its trademark tilt. Subsidence sinkholes can be shored up—or at least made more safe.
“The soluble formations in New Jersey are limestone and dolomite,” says Richard Dalton, a geologist with the New Jersey Geological & Water Survey. “In the southern part of the state we have a formation called the Vincentown, which is a calcarious sand—it’s broken-up shell material. If sinkholes occur there, they’re generally shallow little depressions, maybe a foot deep. There have never been any documented catastrophic sinkholes down there.”
The natural sinkholes, however, tend to cluster in the northern—and more populous—part of the state. “If you look at a geologic map of the state, the main areas are Sussex, Warren, parts of Hunterdon, parts of Morris County, a little bit in Passaic County, and there are some limestones in Somerset County,” Dalton explains. “If you are in a limestone area, and you walk the property, look for shallow depressions that are dish- or funnel-shaped.”