Sinkhole believed from old mine drains Newcastle pond

By: Gus Thomson, Journal Staff Writer
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Newcastle’s Mark Korb is finding that Placer County’s gold-mining past can cause some modern problems.

Korb discovered earlier this week that a sinkhole had opened under a pond he has at his rural Ravine Court property. On Wednesday, he was looking at a drained pond and wondering what to do next.

“The water went straight down,” Korb said. “On Sunday, the water was just about drained, with water rushing down. It’s slowed since then.”

The scenario of a sinkhole in the foothills attracted the attention Wednesday of Sierra College geology professor Dick Hilton.

Hilton visited the hole in the pond and learned that a neighbor of Korb’s dealt with a sinkhole on his property about three years ago. The proximity of the other sinkhole led Hilton to say that he believed Korb’s was caused by a depression likely from a connection into an abandoned mine shaft.

Korb said that he would be considering a number of options – from filling in the pond to plugging the hole and continuing to use the pond.

A 28-year resident of the property, Korb said the pond had been built by previous owners who had intended to raise frogs commercially.

“I have to figure out what to do now,” Korb said.

Hilton traveled to the site from Sierra College to determine what had caused the sinkhole. He initially suspected that rodents had burrowed in two directions to create an underground stream along the bank of the pond. That would be the most common occurrence in the area, he said.

But sinkholes themselves are uncommon in the area, Hilton added.

The other two potential causes were either an underground mine further collapsing or the collapse of a limestone area below the surface.

“It’s probably a mineshaft and it’s going to be a real problem,” Hilton said. “It could be dangerous.”

According to the U.S. Geological Survey, sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds or rocks that can naturally be dissolved by groundwater circulating around them. As the rock dissolves, spaces and caverns develop underground.

The Geological Survey states that sinkholes are dramatic because the land usually stays intact for a while until the underground spaces get too big.

The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania.