Elevated Lake Plains
Okay all you geography and geology students and aficionados: Lehr, North Dakota is situated on an interesting landform, what is it? Some of you have certainly learned that Lehr sits on an elevated lake plain, also called an ice-walled lake plain.
During the Pleistocene Epoch or Ice Age, glaciers repeatedly advanced and retreated over much of the interior of North America. Thickness of ice was variable, but a thickness of 1,000-2,000 feet or more is probably in the ballpark.
At any rate, on top of the ice would be a thick blanket of ground up rock material (rocks/glacial till/rock flour). Lakes would form in the depressions in the ice during warmer periods, and over a few thousand years these lakes would fill in with a thick layer of sediment.
Now visualize all the ice finally melting away. A topographic inversion would result because the lakebed had less ice below it and contains lots of sediment, while the thicker ice was away from the lakebed. The result was an elevated lake plain or ice-walled lake plain.
Their appearance is sometimes compared to a butte because they often are rather flat topped and well above the surrounding landscape. However, some of these elevated lake plains are a bit more difficult to identify, and some features that look like ice-walled lake plains may have been formed in slightly different ways.
As you might expect, these glacial landforms are found mainly on the Missouri Coteau and Turtle Mountains. Elevated lake plains generally make good farmland. It’s no coincidence that many of these areas have been converted to cropland. The soil is generally rich, deep, and free of rocks. You won’t find many rockpiles in these fields! That is particularly evident in the Turtle Mountains where a good portion of the small grains are produced where the forest has been cleared on elevated lake plains. It is also interesting to note that the International Peace Gardens lies on an elevated lake plain.
As you travel the glaciated portions of the state, be on the lookout for elevated lake plains. If you are interested in more information about them, check with the North Dakota Department of Mineral Resources. They have several state, regional, and county publications, some available online, to help us better understand these and other interesting landforms from the Ice Age.
Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.
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