A rare meteor crash site has been discovered in Inver Grove Heights – the first in Minnesota, and researchers hope it will soon be added to the map of other known crash sites around the world.
“I look at rock samples all day and I’ve never seen anything like this before,” said Julia Steenberg, a geologist and research scientist at the University of Minnesota. “Finding and discovering something new is kind of like a breath of fresh air.”
There are about 190 approved sites worldwide, including about 30 in the United States.
“We’re geology geeks and this really excites us,” Tony Runkel said. A lead geologist with the Minnesota Geological Survey said the site was “definitely one of the most interesting finds in his 33 years of surveying.”
The crater beneath Inver Grove Heights is about 2.5 miles wide and may extend to more than 9 square miles in total. It dates back to about 490 million years ago, said Steenberg, who grew up in Dakota County.
The crater itself is hidden several hundred feet beneath the sediments and is not visible to the human eye, he said.
Scientists from the Minnesota Geological Survey, a research arm of the US School of Earth and Environmental Sciences, found the meteorite impact site while updating geological maps of Dakota County in early 2021. Steenberg called it the Pine Bend strike after the Inver Grove Heights area where it was found.
Underlying most of the state’s land are flat layers of glacial sediments. Beneath the glacial layers are sandstone, limestone, and shale. While the scientists were working at Inver Grove Heights, they noticed that the strata, which usually stack up in a predictable pattern, were out of order, and that certain strata appeared to be overturned.
“The more I looked at the field notes, they just didn’t make sense,” Steenberg said.
He recalled locating small, broken grains of sand known as shocked quartz—a common identifier of meteor impacts. According to him, the grains are formed only by a dramatic impact and compression of a meteor impact or a nuclear explosion.
Most of the time, meteors burn up before they hit Earth, but sometimes collisions do occur, Steenberg said.
“There is so much pressure that it creates immediate geological effects,” he said.
For confirmation, Steenberg sent photographs and samples of the sediment to the Museum of Natural History in Vienna, Austria, and the Institute of Geosciences of the University of Brazil. They confirmed that it was, in fact, shock quartz.
Researchers are learning about the site and want to figure out the exact size of the meteor, Steenberg said, and the U hopes to get funding for the work. They plan to publish their findings and maps soon, he added.
Since the site is newly discovered, it has not yet been officially included Earth Impact Databasethough researchers hope it will add up, he said.
In the upper Midwest, impact areas were found in Wisconsin, North Dakota, and Iowa. Rock Science Crater in western Wisconsin, about halfway between the Twin Cities and Eau Claire, is the closest known crater to Minnesota. It is about 3.7 miles in diameter and slightly younger than the Pine Bend Impact, Steenberg said.
Inver Grove Heights spokeswoman Amy Looze said residents are excited to consider Pine Bend Impact a part of the city’s history.
“We are pleased, intrigued and relieved by Ms. Steenberg’s discovery,” Looze said in an email. “I am happy about it [we] could become an important geologic site, wondering if this discovery could give scientists more information needed to predict future meteor impacts on Earth and save our city from having a zero statistical chance of another meteor hitting it.”
