A patch of Swiss cheese-like earth in Frederick collapsed in on itself along Interstate 70 yesterday, creating a large sinkhole that closed the two main westbound travel lanes and caused major delays for travelers.
The sinkhole - described as being the size of a Ford Escort - developed near the South Street exit yesterday morning in a part of the Frederick Valley known for its unstable soils.
State Highway Administration crews, alerted by a state police trooper, arrived at the scene even before the sinkhole fully developed. Highway crews spent much of the day filling the 30-foot-deep hole with stones and a concrete-like grout as traffic crept by on the left shoulder.
Dave Buck, a highway agency spokesman who was at the scene, said the crews were hoping to have the two main travel lanes reopened by the early morning hours today. At one point, Buck said, traffic was backed up about 4 miles, but that fell to 2 miles by the evening rush hour after traffic was detoured onto alternate routes.
The busy interstate, which connects the Baltimore-Washington area with Pittsburgh and the upper Midwest, carries an estimated 79,000 vehicles a day in both directions.
Buck said the problem was discovered about 6:30 a.m. when a state trooper noticed a bump in the roadway and reported it to the highway agency.
When state highway officials arrived at the scene, they found a fissure in the pavement about 3 inches wide and 10 feet long in the right lane and shoulder, Buck said. He said officials closed the right lane and began test borings about 9:30 a.m. when "a bigger section collapsed" - becoming a 14-by-20-foot sinkhole about 30-35 feet deep.
Nobody was injured in the collapse. Buck said additional test borings near the site found no evidence of other sinkholes.
The outcome could have been far worse had the problem not been noticed before the larger sinkhole developed. "It's big enough that it would have been very bad," said Buck, who described the hole as being the size of a passenger car such as an Escort.
Buck said sinkholes are common in the Frederick area but not on I-70 itself. He explained that the area has large limestone deposits that are prone to collapse after periods of heavy rain. Unlike potholes, which develop on the surface, sinkholes start from the bottom, he said, making them difficult to predict.
James Reger, project director for the Maryland Geological Survey, said the Frederick Valley is known as one of the areas of the state most prone to developing sinkholes. He said scientists using satellites have mapped more than 1,800 sinkholes in the valley.
Reger said that the limestone bedrock in the valley has been dissolving for thousands of years, forming cavities covered by a thin layer of topsoil.
"Some of the limestone beds are more Swiss-cheesy than others," he said.
After a heavy rain, the geologist said, "they just collapse into the void that's already there."
Reger said state highway officials have known for years that the Frederick Valley is susceptible to potholes and has done what it can to prevent them.
"To find them all, you'd be surveying like no one's every surveyed. It's expensive," he said.
Road-building activity, which has been extensive around Frederick, can sometimes contribute to sinkhole formation by changing the way water in the vicinity drains, Reger said. To alleviate the problem, he said, the state has been building pumping stations in the area to carry away highway runoff.
Other areas of the state that are susceptible to sinkholes include the Hagerstown Valley and the Wakefield Valley in Carroll County.
But none, he said, is on a par with the Frederick Valley,
Sinkholes can be deadly when they develop suddenly under roadways. In 1994, a Westminster city employee died after his van plunged into a 45-by-18-foot sinkhole that opened under Route 31 in the Wakefield Valley as he was traveling toward New Windsor at night.
"It's a problem that won't be going away soon, I think. It's a comment on man and nature," Reger said. "Nature's going to win."