What goes "boom" in the night? The exhausted residents of Clintonville, Wis., wish they knew.
Since Sunday evening, mysterious sounds have been jolting the city awake, and no one can explain where they're coming from.
"People describe them as booming, thunder-like noises -- vibrating, shaking," Lisa Kuss, Clintonville city administrator, told msnbc.com. "The most extreme one I experienced was at 10 p.m. Monday night in our utilities room, and it was a bam."
That night, city officials received nearly 100 calls about the unexplained shaking. Alarmed, city officials tested gas levels, investigated sewer systems and landfills, and checked on city dams. Everything came back normal.
"People are, number one, somewhat scared," Kuss said. "But as time passes, they're more frustrated than scared; there are a few that have left. They say, 'We need to get some sleep.' They're frustrated it's elevated at night."
On Sunday night, the booms happened at around 8 p.m., 10 p.m., midnight, 1 a.m., and 2 a.m., according to a press release from the city. They came back again Monday night, and after a brief reprieve overnight Tuesday, they returned early Wednesday.
The city's 4,600 residents have been invited to a meeting Wednesday night at the high school to discuss the situation, even though there isn't much news to tell them.
"The only thing we can really conclude is a lot of things it isn't," Kuss said. "It doesn't seem to be related to our systems. It's not the military. It's not a mining pit that's being blown up. We've never had any earthquakes; we've had a couple of people tell us we're on a fault line, but we have no way to confirm that."
A professor's theory: Groundwater
According to Steve Dutch, a professor of geoscience at University of Wisconsin-Green Bay, Clintonville doesn't lie on a fault line.
"The USGS is not picking up any earthquakes in Wisconsin. These appear to be purely local events. People 50 feet away don't feel anything," he said.
But he has another idea.
"After thinking about it, I would start looking at the movement of groundwater," Dutch told msnbc.com. "If some of that water is being removed, from pumping, maybe, the rocks are settling a bit, and that's producing some of these sounds."
Groundwater is precipitation that has seeped through soil and is stored in rocks. Dutch theorizes that the city utlity might be pumping water at night, causing shifts and vibrations, and explaining why the booms are more frequent when people are trying to sleep.
Mysterious noises and ground vibrations are unnerving residents in Clintonville, Wis. WGBA-TV's Brian Miller reports.
"It might have to do with water usage, water flowing back at night, causing the noises. Or maybe pumping rates are cheaper at night," he said.
Further supporting his theory is the type of rock beneath Clintonville: sandstone.
"People have suggested sinkholes [are causing the noises]," Dutch said. "That's pretty unlikely because the rocks under Clintonville are not limestones or soluble rocks that would produce sinkholes."
Dutch, who has a Ph.D. in structural geology, said he's never heard of anything like Clintonville's booms.
"I'll get a call from somebody who heard a boom at their house, and I just have to say, 'I can't really tell ya,' but not on this scale," he said. "Sometimes in science, we don't really know."
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