Kirk A. Luther, 29, of Enola, Pa., driving a 1989 Toyota sedan, and Kathryn L. Kelly, 48, of Chambersburg, Pa., driving a 1988 Oldsmobile, managed to bring their cars to a stop on the side of the road north of the accident, police said.
A 1992 Eagle, driven by Joseph A. Wiendl, 26, of Ponte Vedra Beach, Fla., came to rest in both northbound lanes of the highway about 15 feet north of the hole, police said.
Wiendl was taken to Chambersburg Hospital with moderate injuries, police said.
Kelly and her passenger, Mildred B. Kelly, 71, of Chambersburg, suffered minor injuries and were taken to Chambersburg Hospital, police said.
Luther was not injured, police said.
Wiendl's car sustained severe damage and the other two vehicles sustained minor damage, police said.
Most of the damage to the vehicles was to the undercarriages, Lenherr said. Firefighters from Fayetteville and Shippensburg, Pa., had to mop up some spilled antifreeze, he said.
Police closed down I-81 to clear the accident and to allow a state Department of Transportation road crew to start filling in the hole with dirt and gravel.
Fire police routed traffic off of the interstate onto Old Scotland Road near the Chambersburg Mall at Exit 8.
By 3:15 p.m., traffic was allowed to pass on the left lane as the road crew put a coat of asphalt over the filled-in hole.
State transportation officials could not be reached for comment.
Chambersburg civil engineer William A. Brindle said a sinkhole is caused by erosion of soil, in this case beneath the road bed, from a natural underground drainage system.
As the drainage channel gets larger, combined with vibrations from the traffic, it eventually creates a weak spot in the soil and caves in, he said.
"It's very possible it could have been caving in under the concrete for a long period of time," Brindle said.
It's not uncommon for sinkholes to develop in limestone soil, which is found in that part of Franklin County, he said.