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This anaglyph was produced by Ray Sterner of the Applied Physics Laboratory at Johns Hopkins University using USGS DEM data.

The east-west distance across the anaglyph is approximately 130 miles, and the north-south distance is about 250 miles. The image covers portions of North Dakota, South Dakota, Minnesota, and Iowa. Although the actual vertical relief across the image is something less than 1000 feet, the vertical exaggeration perceived in the image is much, much higher (300X).

The Coteau des Prairies (Prairie Coteau) is the prominent, wedge-shaped landform whose point just juts into southeastern North Dakota. Although the Coteau is cored by bedrock, outcrops of bedrock are limited. Instead, the feature is draped by glacial deposits whose thickness averages over 400 feet.

During the last (Wisconsinan) glaciation, ice of the Red River Lobe was split by the Coteau into two lobes: the Des Moines Lobe, which passed southeastward toward Des Moines, Iowa, and the James Lobe, which passed southward toward the Missouri River Valley. Glacier ice did not completely cover the Coteau during this glaciation; instead, it lapped up and over onto both flanks, leaving prominent moraines (clearly visible, but unlabeled) along the upper surface that trend parallel to the Coteau itself.

Ice retreated northward from the Big Stone Moraine by about 11,600 years ago. At about this time, a massive ice-dammed lake (Glacial Lake Agassiz) formed in what is now the Red River Valley. During much of its early history, Lake Agassiz drained southward into the Minnesota-Mississippi River system via a valley now occupied by Lake Traverse, Browns Valley, and Big Stone Lake.

A north-south continental divide (unlabeled) somewhat parallels the North Dakota/South Dakota border in this image. North of this divide, waters drain into the Red River of the North, ultimately to arrive at Hudson Bay via the Nelson River. South of this divide, waters drain into the Missouri River, ultimately to arrive at the Gulf of Mexico via the Mississippi River.

While most of this image reflects a rather "soft" topography due to glacial erosion and burial, not all of this landscape was glaciated. The Missouri River here marks the approximate limit of glaciation ; note the prominent change in landscape nature southwest of the river.

Click here for additional graphics on the Prairie Coteau.

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