Why a 40-foot-deep sinkhole swallowed a 40-foot stretch of NJ highway

UPDATE: The closed stretch of Route 80 reopened 8 a.m. Monday.

From the Department of Transportation:

Repairs included excavating and stabilizing the 40-foot by 40-foot sinkhole, before a full-depth reconstruction of the roadway. To rebuild the road, crews installed a base of stone aggregate, wire mesh topped with more stone and a concrete layer. That was topped with additional fill and compacted before several layers of asphalt were put down to rebuild the road. In addition, the slope was reconstructed and guiderail repairs were completed.

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WHARTON — A portion of a North Jersey interstate will remain closed indefinitely after a sinkhole swallowed the shoulder on Thursday morning. State transportation officials now know what caused it.

The sinkhole on the eastbound side of Interstate 80 measures 40 feet deep by 40 feet wide. It collapsed 7:35 a.m. Thursday just past Exit 34, near mile marker 34.

No vehicles fell into the hole but it continues to tie up traffic. Photos from the scene show extensive damage.

Cause of the sinkhole

The Department of Transportation said the sinkhole was caused by the collapse of an abandoned mineshaft.

Morris County has a large concentration of abandoned iron mines dating back to the 18th and 19th centuries. The municipality of Mine Hill gets its name from this history and Rockaway Township uses an anvil in its emblem.

A Department of Environmental Protection map shows that this part of Route 80 passes directly over at least two or three of these abandoned mines.

How long repairs will take

State transportation officials on Friday did not have a complete timeline for the repairs.

Commuters will be directed to Route 46 or the following detours.

Route 46 eastbound alternate route

↪ Motorists on I-80 eastbound are advised to take Exit 28/Route 46 eastbound to Route 10/Ledgewood/Lake Hopatcong, which is several miles before the closure

↪ Continue on Route 46 eastbound

↪ Stay in the left two lanes to turn left at the traffic signal to continue on Route 46 eastbound

↪ Turn left onto Route 15 northbound in Dover back to I-80
or

↪ Continue on Route 46 eastbound for about 12 miles and stay left for I-80 eastbound

I-80 eastbound detour

↪ Motorists on I-80 eastbound are being directed to take Exit 34 to Route 15/Wharton/Dover/Sparta

↪ Stay right following signs for Route 15/Jefferson/Dover/Sparta

↪ Stay in the left lane on North Main Street to Route 15 southbound/To I-80/Dover

↪ Merge onto Route 15 southbound

↪ Stay left to take the exit to I-80 eastbound