Neighborhood NewsGreen Space & The RiverLocal Culture

Evidence for Giant Prehistoric Flood discovered in St. Paul

By Greg Brick, PhD

Highland Creek is among the more obscure streams in St. Paul, largely because it has been diverted underground by city engineers. But this stream has long harbored a secret—it was the scene of a giant prehistoric flood. Much of the evidence has been lying around in plain sight for years, but the dots have never been connected. Until now.

Glacial lake sediments stretch from what is now Cretin-Derham Hall south to the Highland Golf Course, the record of a vanished lake the size of Lake Phelan. The 1992 geologic atlas describes these as “deposits of a former lake that may have been partially confined by stagnant ice.” This north-south elongated lake formed in a former ice-block depression of the last lobe of the last ice sheet. You get a sense of just how large this “ice bowl” is by looking down into it, toward the east, from the Highland Water Tower. The lake could have been as much as 100 feet deep. At some point, the ice wall along one side collapsed, catastrophically releasing the lake volume all at once—this is called an outburst flood. But where did this flood of water go to? The Fort Road neighborhood.

Lying directly in its path, there’s a giant ravine largely unknown to the public because it is difficult to access, and filled with dense vegetation. It occupies the parkland between Circus Juventas on Montreal Avenue, and Mickey’s Diner on Fort Road. It may even account for the kink in Fort Road at this point, detouring around what might have been massive remnant debris in pioneer days. This ravine is the giant slash mark carved by the outburst of glacial meltwater. Together with the ice lake sediments, it all paints a picture of a truly colossal flood in this part of St. Paul.

Greg Brick, Ph.D., mapped thousands of springs around the state while employed as a hydrogeologist by the Minnesota Department of Natural Resources and is the author of several books on Midwestern caves.

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