Underground explorer Greg Brick finds evidence of an ancient glacial lake in Highland Park

Whenever researchers talk about historic St. Paul, chances are they’re referencing stately old homes or long-ago lost architecture. Greg Brick spends a lot of his time looking for prehistoric St. Paul in rocks, sand and sediment.

The Highland Park native and former Department of Natural Resources geologist is pretty excited about what he’s found near his old stomping grounds: evidence of a glacial lake bursting 10,000 years ago. He used a map of ice age-era St. Paul prepared by geologist Carrie Jennings in 1992 and compared it to a ravine that seemed too large to have been carved by the small stream moving through it. For Brick, the finding ranks right up there with the discovery of the skeleton of a giant beaver in Hidden Falls Park in 1938.

Brick has spent decades exploring the Twin Cities, searching for hidden springs, forgotten caves and geologic clues to the area’s origins. Eye On St. Paul recently met with Brick near the Highland Park Water Tower before moving on to Mickey’s on W. 7th to learn more about the ancient past. He has dubbed his discovery “Mickey’s Ravine” because of its proximity to the diner. This interview was edited for length.

Q: What is the new finding here?

A: There was a flood in prehistoric Highland Park that carved out some features here that we’re very familiar with but didn’t realize where they had come from. This follows a pattern in geology called an outburst flood. Glacial Lake Agassiz spilled out and carved the Minnesota River Valley. I found a similar example here at Highland Creek.

Q: Where did Highland Creek run?

A: It ran for a mile and a half from the north edge of what is the Highland golf course, then down through the golf course, crossed over Montreal [Avenue] and then came down through this ravine below Circus Juventas and it flows under Shepard Road and into Crosby Regional Park. Then it flows out to the Mississippi River where the I-35E bridge crosses. It’s hard to see because there’s a big plateau of fill material that’s in Mickey’s Ravine, and that’s what Circus Juventas sits on.

Q: How did you figure out what had created this ravine?

A: When I followed the stream near Circus Juventas, I had a negative eureka moment. This tiny little creek, you can barely hear a trickling behind Circus Juventas, and yet here’s this gigantic 400-foot-wide chasm. So you come to Carrie’s map and she mapped a glacial “meltway” here, coming down through the ravine. And I said, “Aha! This was an ice-walled glacial lake on which the ice failed on one side.” And there was an outburst flood that carved this ravine.

Q: When would that have happened?

A: Ten thousand years ago, in the waning phases of the ice age.

Q: So at some point the ice wall that formed the glacial lake burst?

A: Yeah. It either thinned out or floated out. It could have given way like a dam breach. Or it could be that the ice just floated up, like with Icelandic glaciers. As soon as that glacier starts floating, all that meltwater comes pouring out. Imagine all the water in Lake Phalen, and somebody pulled the cork and all that came out at once.

Q: What makes this finding so significant?

A: We know how these outburst floods work, like with glacial Lake Agassiz. It’s interesting to know we had one right here in St. Paul. Because I don’t know of any other example of one in the Twin Cities area. I think that’s exciting.

Q: How does this change your understanding of the geology here?

A: We can start putting together a picture of prehistoric St. Paul. You had roaring waterfalls, giant beavers. You had this catastrophic lake drainage. At that time, there would have been no one living here. Not even Paleo-Indians.

Q: But the fauna would have been in danger, right?

A: Those poor extinct beavers.

Q: So, give us a picture of what St. Paul looked like 10,000 years ago.

A: I’m tempted to merge into political parody here and talk about City Hall. [laughs] But I think we can. Based on pollen data and occasional paleontology finds, you can kind of come up with an analog environment. Maybe it would be something equivalent to up on the tundra. Somewhere today like near Hudson’s Bay. With giant beavers.