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Wisconsin Potholes and Sinkholes

© Peggy Hoehne

Early lead miners in Wisconsin were called "Badgers," because they often slept in holes in the ground like a badger. That is rather appropriate considering all of the holes in the ground Wisconsin has to offer. This month we will look at three rather large types of holes in the ground; Glacial Potholes, Prairie Potholes, and Sinkholes.

Glacial potholes carved by glacial melt during the last ice age can be very large. About 10,000 years ago the last glacier was retreating from this area. Known as the Wisconsin glacier, this glacier included the great glacial lakes, which were much larger than, but in the basin of, present-day Lake Superior. When they melted they released a tremendous amount of water to gush southward carving its way through the softer earth and rocks. Only the very resistant basalts were able to withstand the torrent.

In areas where there was hard basalt, sharp cliffs were left such as you can see along the St Croix River. The water was forced into a narrower valley between the cliffs and rushed even faster and more powerfully. The water eddied and swirled about the hard bedrock carrying gravel and small rocks with it. Some of these rocks got caught up in a whirlpool action and gradually wore holes down into the rock creating potholes.

There are as many as 100 of these potholes in Interstate State Park which lies partially in Minnesota and partially in Wisconsin on both sides of the St Croix River, near St Croix Falls, Wisconsin. Some of these potholes are fairly small, but others are large enough to walk in. One, the largest, known as The Bottomless Pit, is 68 foot deep and is the deepest explored pothole in the world. Others potholes in the area are up to 40 foot deep. Interstate Park contains more glacial potholes in a smaller area than any other place in the world.

There are a number of hiking trails in the park from which you can see the potholes for yourself. You can take a self-guided one-forth mile trail starting from the Visitor's Center. The Pothole Trail winds through the St Croix Dalles and into one of the giant potholes.

More information on Interstate Park and potholes - http://www.geotimes.org/apr04/Travels042...

Prairie Potholes are quite different, but they also owe their existence to the glaciers. As the ice withdrew, it left behind thousands of depressions in the ground. Prairie potholes are found primarily in the Upper Midwest, especially North Dakota, South Dakota, Wisconsin, Minnesota, and the lower portions of Alberta, Saskatchewan, and part of Manitoba in Canada. These depressions hold water and provide resting places, feeding areas, and nesting habitats for not only waterfowl, but a number of other prairie creatures. The wetlands, primarily freshwater marshes, are critical to the survival of migratory waterfowl.

The copyright of the article Wisconsin Potholes and Sinkholes in Wisconsin is owned by Peggy Hoehne. Permission to republish Wisconsin Potholes and Sinkholes in print or online must be granted by the author in writing.