HARRISONBURG -- Dr. Eric Pyle, a James Madison University geology professor, said sinkholes happen quite often and quite simply.
"Rain water is a little bit acidic. As it goes through the soil, it gets a little more acidic," he said.
In a demonstration, Dr. Pyle put watered down acid onto the surface of limestone. In just a short time, the rock showed signs of breaking down.
"Limestone doesn't bend, so any stress causes lots of fractures and cracks. That's a pathway for the acidic water to get into the rock. Where it's dissolved enough, it creates a cavity or a void. Where that's close to the surface, if it's large enough, it's like a bridge collapsing. If you remove everything underneath it, the weight of everything above simply falls in."
In Pennsylvania, a sewer line burst in two places and created a 30 foot wide sinkhole. Dr. Pyle said it was another main cause.
"As you increase the flow rate, that's more acid going past rock that dissolves very easily."
Limestone is prevalent in most of the Valley.
"As humans spread out into more and more areas, they're going places where people haven't lived or build houses, or visited frequently, and that simply allows the intersection of people and a natural phenomenon, which unfortunately has disastrous consequences."
Dr. Pyle said he wouldn't worry about anything too much. He said most of the caverns in Luray and Grottoes were formed in a similar way. He said the surface doesn't always collapse when rock is removed.
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