Site of rare meteorite impact discovered in Inver Grove Heights

A rare meteor crash site has been discovered in Inver Grove Heights — the first found in Minnesota — and researchers are hoping it soon will be added to the map of other known crash sites around the world.

"I look at rock samples all day long, and I've never seen anything like this before," said Julia Steenberg, a geologist and research scientist at the University of Minnesota. "It's sort of like a breath of fresh air to find and discover something new."

There are about 190 confirmed sites worldwide, including about 30 in the United States.

"We're geology nerds and this gets us really excited," said Tony Runkel. lead geologist at the Minnesota Geological Survey, who said the site "for sure" is one of the most intriguing finds in his 33 years with the survey.

The crater under Inver Grove Heights is about 2.5 miles wide and could stretch over 9 square miles in all. It dates to about 490 million years ago, said Steenberg, who grew up in Dakota County.

The crater itself is hidden several hundred feet underground beneath sediment, and can't be seen by the human eye, she said.

Scientists with the Minnesota Geological Survey, the research arm of the U's School of Earth and Environmental Sciences, found the meteorite impact site in early 2021 while they were updating geologic maps of Dakota County. They named it the Pine Bend Impact, after the area of Inver Grove Heights where it was found, Steenberg said.

Underneath most of the state's soil are flat layers of glacial sediment. Beneath the glacial layers are sandstone, limestone and shale. As scientists worked in Inver Grove Heights, they saw that the layers, which usually are stacked in a predictable pattern, were out of order and certain layers appeared to be overturned.

"The more I looked at the records right in that area, they weren't making any sense," Steenberg said.

She recalled locating tiny, fractured grains of sand known as shocked quartz — a common identifier of meteor impact. The grains are created only by the dramatic shock and compression of a meteor's impact or a nuclear explosion, she said.

Most of the time, meteors burn up before hitting the Earth — but sometimes a collision occurs, Steenberg said.

"There's such intense pressure associated ... that it produces instantaneous geological effects," she said.

For verification, Steenberg sent photos and samples of the sediment to the Natural History Museum in Vienna, Austria, and the University of Brazil's Institute of Geosciences. They confirmed that it was, in fact, shocked quartz.

Researchers are learning about the site and want to figure out the exact size of the meteor, Steenberg said, adding that the U hopes to obtain funding for the work. They plan to publish their findings and their maps soon, she added.

Because the site is newly discovered, it's not yet included on the official Earth Impact Database, though researchers hope it will be added, she said.

In the Upper Midwest, impact sites have been found in Wisconsin, North Dakota and Iowa. The Rock Elm Crater in western Wisconsin, about halfway between the Twin Cities and Eau Claire, is the closest known crater to the Twin Cities. It is about 3.7 miles in diameter and slightly younger than the Pine Bend Impact is thought to be, Steenberg said. The Decorah crater in Decorah, Iowa, is the closest to Minnesota.

Amy Looze, a spokeswoman for Inver Grove Heights, said residents are excited to count the Pine Bend Impact as a piece of the city's history.

"We are pleased, intrigued and relieved by Ms. Steenberg's discovery," Looze said in an email. "Pleased that [we] could become an important geological site, intrigued that the discovery could give scientists more of the data they need to predict future meteor impacts on Earth and relieved that there is zero statistical chance of another meteor ever hitting our city."