MANKATO — A quarry that was accused in April of causing an earthquake-like tremor felt across a broad swath of Mankato has had its explosives license suspended Tuesday after a blast that sent rocks larger than bowling balls soaring into a nearby neighborhood.

One rock knocked a hole in the siding of a home on Harper Street, another sheared off large tree branches and a witness described the sound of dozens of rocks hurtling through treetops and off of roofs.

The Mankato Department of Public Safety immediately suspended the quarry's blasting permit following the 10:35 a.m. explosion. No one was injured, but the potential for harm was obvious, according to Jeff Bengtson, deputy director of the Public Safety Department.

"Anything that could pose a safety hazard I think warrants suspension of the permit to ensure a thorough investigation," Bengtson said. "... A 12-inch rock would be hazardous to people's welfare."

Jordan Sands, which operates the Coughlan Companies-owned quarry along the Minnesota River just south of Highway 14, had its permit suspended in the spring after an April 25 blast was immediately followed by a temblor strong enough to rattle buildings across the Minnesota River valley. More than two dozen homeowners reported damage that they attributed to the tremor.

The city suspended the company's explosives permit for 60 days, the maximum allowed, but allowed blasting to resume after an investigation found no negligence by Jordan Sands in the April 25th incident.

Tim Slipy, who lives on Harper Street next door to the home that was struck Tuesday by one of the larger flying rocks, said the detonations are frequent enough — at least every couple of days — that he gave it little thought when the quarry's warning horn sounded Tuesday morning.

"The horn blew. They do three blows before a blast and about a minute later it goes off," Slipy said. "This one, they did three blasts and about five seconds later there was a blast."

There was another difference with Tuesday's detonation.

"I was like, 'What's that sound?'" Slipy said. "It was the rocks coming in. You could hear it flying through the trees. ... Small ones, big ones. You're talking 20, 30, maybe 50."

Within minutes, quarry workers were in the neighborhood, picking up rocks and tossing them into the trees that separate the Germania Park neighborhood from the quarry. They may have just been trying to be neighborly and clean up the mess, but Slipy didn't think so.

"The quarry guys came up and threw 'em in the woods," he said. "... They were trying to cover it up is what it looked like to me."

But a community service officer employed by the Mankato Department of Public Safety was stationed, as is the city's protocol for quarry blasts, just down Harper Street, and city employees also quickly descended on the scene, according to Slipy. The building struck by one of the larger rocks is city-owned subsidized housing.

Julie Kreiselmeier said the quarry blasts always shake their home at 601 Harper Street and make her jump. But she wasn't there for Tuesday's blast and was feeling fortunate because the missile that left a crater on the side of her home hit just above her daughters' bicycles.

"I was with my kids at Grandma's," Kreiselmeier said. "Seriously lucky, because my kids are always out here playing. Just shocked. We're just in shock now."

The rock that hit the house was no longer on site, possibly removed by city officials as part of the investigation. Others were still in place on their yard, and there was at least one large divot in the grass.

"It could kill someone," Kreiselmeier said, thinking of her 12- and 10-year-old daughters and pointing to the window about six feet directly above where the rock hit. "That's their bedroom window right up there."

While the impact didn't punch all the way through the wall, it knocked over possessions inside the home — wrecking a sand ceremony vase from her wedding.

David Kreiselmeier was relieved to hear that the city had suspended the company's blasting permit.

"That's good because it's getting crazy," he said. "I have words to say (about the company) but I'm going to keep it to myself."

"It's obviously not safe for residents here," his wife said.

Jordan Sands Vice President Brett Skilbred said there was little he could say Tuesday night until more is learned about the cause of the flying debris.

"We're very concerned about the event today," Skilbred said. "Safety continues to be our No. 1 priority. ... We'll continue to investigate this and bring forth more information as it becomes available."

Tuesday's problems came seven weeks after the company announced that an engineering firm it hired to investigate the April 25 incident determined that a natural earthquake — not an explosion at the quarry — caused the tremor, which registered 2.8 on the Richter scale.

The determination was widely ridiculed in the community because the alleged earthquake happened virtually simultaneously with a blast at the quarry and because earthquakes are extremely rare in southern Minnesota.

The U.S. Geological Survey said the incident, based on seismological data, was likely due to a quarry blast, and several other geologists agreed that the raw data shows an explosion caused the Mankato area to shake.

City officials, while not endorsing the earthquake theory, said their investigation determined "there was no negligent discharge of explosives in the quarry on April 25."

Blasting was allowed to resume but with additional conditions, including "control of flyrock" and more monitoring of ground movements. And Jordan Sands, which announced more than a year ago that it was winding down operations at its quarries within the city, pledged to end all blasting in the quarry by Dec. 29.

Tuesday's blast was witnessed by a Department of Public Safety employee, as is the procedure for all explosions at the quarry.

"Our community service officer was on site as usual to observe the blast and she notified us that some rocks had left the quarry," Bengtson said, adding that he had no preliminary opinions on why the explosion caused such large stones to fly from the property. "We're still working on the cause right now."

The permit to use explosives will be suspended indefinitely while the investigation continues.

Slipy said he was angry after Tuesday's explosion and "chewed out" the Public Safety officials before later apologizing.

"It's not their fault," he said.

He has a different opinion of the quarry operators.

"I don't know what they were thinking," Slipy said. "I mean, they don't know what they're doing. They can't be that hard up for rocks to endanger people's lives."

While Germania Park residents have grown so accustomed to the blasts that they barely pay attention, Slipy said he wished he'd followed the lead of the neighborhood's pets — who tend to seek shelter when the quarry warning horn sounds.

"If I'd known there was going to be debris, I'd have gone in the garage like the dogs and cats," he said. "They were all in the garage. I was the only idiot outside painting."

But Slipy came through unscathed even as rocks — some too heavy to lift — rocketed through the air above and beside him. So he and another neighbor decided maybe Lady Luck was shining on them.

"Geno's picking up the lottery tickets today," he said. "The Mega Millions is at $350 million."

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