Massive sinkhole formed on possible mining site

"It appears to be an old exploratory mine shaft, probably for copper, maybe granite, dating back to the 1800s," Marietta public works director Dan Conn told the AJC. "There are no records or map that show that. But that's what our geo-technical engineer seems to think."

By the time the sinkhole stopped spreading Tuesday morning, it measured 30 feet wide, 40 feet long and nearly 25 feet deep. It attracted a slew of interested onlookers, including Mayor Steve Tumlin.

The house, in the 1100 block of Charlton Trace, does not appear to be in danger of falling in, Conn said. The sinkhole remains about 15 feet from the roadway, and about 25 feet from a neighboring house.

"There seems to be rock or dense material all the way around the hole, enough that it seems it's basically stable," Conn said.

Homeowner Lisa Thompson, who could not retrieve her car from the garage, declined to be interviewed.

When the first tree fell in around 6 p.m. Monday, it scratched her face "but didn't injure her too bad," Conn said. Firefighters and other city workers monitored the sinkhole, which doubled in size overnight.

Surging rainwater is the most common cause of sinkholes. "We expect that's the case here but we can't see where the water is coming from or going to," Conn said. "We hope to find that out with additional analysis of the data collected today."

He said it's the largest sinkhole he's ever dealt with.

-- Staff photographer Bob Andres contributed to this report.

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