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I-80 Collapse: 300 Years of Mining History Behind Massive Roadway Sinkhole

March 10, 2025

traffic on highway with trucks and cars — Delays are common on I-80 east near Exit 34, with no date set for the highway’s reopening. Photo by Joe Phalon.

I-80 Traffic Jams Started 300 Years Ago

The baseball diamond-size hole in I-80 that has made eastbound commuting a nightmare for many Warren County drivers was 300 years in the making.

But first, an update: Gov. Phil Murphy, along with numerous other state officials, visited the site over a collapsed iron mine Saturday morning, where he announced he was declaring the cave-in a disaster area.

A state of emergency declaration allows the state to apply for federal funding through the Federal Highway Administration.

As for the most pressing question — when will I-80 reopen? The answer remains uncertain. The highway has been closed since Feb. 8, with no reopening date yet announced.

route 80 highway signs for Del Water Gap — I-80 eastbound traffic can be traced back to the Revolutionary War. Photo by Joe Phalon.

Meanwhile, crews are conducting 24-hour drilling and grouting work on I-80 eastbound between Exit 34 and the bridge over Route 15 in Wharton Borough, according to the New Jersey Department of Transportation.

This work is stabilizing the roadway and helping engineers better understand the conditions necessary for repairs, DOT Commissioner Fran O’Connor said.

The department is continuing to explore all available options to restore mobility impacted by the emergency construction. In addition, NJDOT has been in communication with FHWA and will continue to do so as repairs continue.

“Once we have a better understanding of the subsurface conditions, we can finalize the design for a repair. In the meantime, we are exploring all options to improve traffic through the area while construction is ongoing,” said O’Connor.

The void identified last week beneath the center lane of I-80 eastbound has been stabilized, according to DOT officials. However, additional work will be needed to fully repari the area, and the extent of those repairs is still being determined.

Over the weekend, construction barrier and fencing were installed between the median and I-80 westbound to provide additional safety during the grouting operations.

As of Wednesday, March 5, drilling had been completed at 82 locations — about 61% of identified sites in the immediate area that require remediation. Of those, 57 locations, or more than 42%, have been filled with grout. These areas are not all voids, but rather locations requiring investigation. The number of sites that need further review may be adjusted as work progresses, according to the DOT.

While the term “sinkhole” has been used widely to describe the collapse, the geological definition of a sinkhole doesn’t quite apply. The U.S. Geological Survey defines a sinkhole as “a depression in the ground that has no natural external surface drainage. Basically, this means that when it rains, all of the water stays inside the sinkhole and typically drains into the subsurface.”

Sinkholes typically form in areas with limestone, salt or other soluble rock, where underground erosion creates voids that can eventually cause the surface to collapse.

The holes in I-80, however, are not the result of natural geological processes. Instead, they are collapses into abandoned mineshafts.

Iron mining began at the Mount Hope Mine, just a few miles from the I-80 collapse site, in 1710. The New Leonard Mine, part of the Mount Hope complex, was the deepest mine in the area at 2,694 feet.

Hundreds of mines were developed across the north Morris County and Warren County region where iron was found to be great quantities. During the Revolutionary War, more than 400 mines were operating at one time. In total, nearly 30 million tons of iron ore were extracted from the region.

Mining declined in the early 20th century when the iron was exhausted. Many mines were simply abandoned, their deep honeycombs of mineshafts left unsealed.

Over time, these underground tunnels and chambers have weakened, sometimes leading to sudden collapses like the one beneath I-80.

One such abandoned mine, the Huff Mine, was active between 1855 and 1910, according to a state Department of Environmental Protection map. The cave-in at Exit 34 of I-80 suggests that, in a way, that mine is active once again.

Joe Phalon, Contributing Writer

Contributing Writer

Joe brings decades of journalism experience to the Ridge View Echo, covering everything from local school boards to the U.S. Supreme Court. A former National Law Journal editor and Columbia Law School press officer, he now enjoys telling community stories in Blairstown, where he lives with his wife, Rose, and their two dachshunds.