Corrections & clarifications: This story has been updated to reflect that portions of the interstate have been closed for about six weeks.

The third sinkhole since December has opened up on Interstate 80 in north New Jersey, adding even more closures and headaches to the region.

The 15-by-15-foot sinkhole opened up just after 5 p.m. Wednesday in Morris County, about 25 miles northwest of Newark, according to Steve Schapiro, a spokesperson for the New Jersey Department of Transportation. It opened up in the median in a work zone on eastbound I-80, the department said on its website.

The sinkhole is the latest plaguing the state recently, leaving portions of I-80 closed for about six weeks, Schapiro said.

According to the department, the two other recent sinkholes reported include:

• Dec. 26: A 40-by-40-foot sinkhole developed in the right shoulder of eastbound I-80 near milepost 34. Crews worked through the Christmas holiday weekend to repair the sinkhole and had the highway reopened by Dec. 30.
• Feb. 10: An 11-by-11-foot sinkhole opened on eastbound I-80 at while crews were conducting soil tests. Crews excavated and stabilized the 4-feet-deep sinkhole.

The department closed the eastbound lanes in February after the second sinkhole opened, and the latest sinkhole led officials to close the westbound lanes out of caution. Crews worked overnight to stabilize the area around the median after Wednesday’s incident.

“It has not yet been determined when I-80 westbound may be safe to reopen,” the department said.

Repairs are underway on the latest sinkhole, officials said, adding that New Jersey Gov. Phil Murphy declared a state of emergency for Morris County on March 8 for federal funding. 

Next, officials will apply for emergency federal funding from the Federal Highway Administration.

How have officials dealt with the sinkholes?

After the sinkhole formed in February, the transportation department immediately began geotechnical testing on eastbound and westbound I-80 to figure out what was happening with the roadway.

The department is also drilling and grouting to stabilize eastbound I-80. This phase requires crews to fill holes and small voids, and figure out which areas need the most extensive repairs. 

The department of transportation has already pinpointed 90 locations on the interstate that need to be assessed due to potential instability, reported the Bergen Record, part of the USA TODAY Network.

As of Friday afternoon, crews were in the drilling and grouting phase. Once that’s done in mid-April, crews can begin to repair the latest sinkhole.

Crews will excavate the area and install a base of large stone with a wire mesh on top, the department said. They will then add more stone and a concrete layer over the wire mesh. Next, they’ll do more filling and soil will be placed on top of the concrete and compacted. Several layers of asphalt will then be added.

“Once the repair begins, it is expected to take approximately one month,” the department said.

Still to come are:

• Reopening westbound I-80
• Sinkhole repairs
• Quality assurance testing
• Monitoring system installation to track surface and underground conditions as part of the repair
• Milling and paving so drivers have a smooth surface before the lanes reopen
• Reopening eastbound I-80

The transportation department has listed detours and routes for drivers on I-80 at www.tinyurl.com/NJDetours.

What causes sinkholes?

The three sinkholes formed due to the collapse of an abandoned mineshaft, Schapiro told USA TODAY.

Timothy Bechtel, a senior professor of geosciences at undefined in Lancaster, Pennsylvania, told the Bergen Record that most sinkholes are caused by precipitation and begin with a manmade void or a natural cave.

He added that sinkholes are a lot like hourglasses. 

“When you first flip it over, there’s unconsolidated material,” he said. “There’s sand at the top and down below, there’s an opening.”

Floods and large amounts of rainfall push soil downward, eventually creating a sinkhole at the surface.

While the National Weather Service has said that New Jersey has received less overall precipitation than normal over the past year, the storms have been quite intense, reported the Bergen Record. 

There were also multiple strong earthquakes last spring, although Bechtel said the sinkholes in New Jersey would’ve developed sooner if the earthquakes were part of the cause.

“Earthquakes can loosen the soil,” he said, but “I’d expect that they’re probably not implicated in these sinkholes.”

Saleen Martin is a reporter on USA TODAY’s NOW team. She is from Norfolk, Virginia – the 757. Email her at [email protected].