Montana Earth Science Picture of the Week

Glacial Trough in Southcentral Montana

This photo was taken along the Beartooth Highway about 20 miles southwest of Red Lodge (as the crow flies) and 5 miles north of the Wyoming border. A portion of the highway is visible just to the left of the photo’s center. The Beartooth Highway and the Going To the Sun Road in Glacier National Park are two of the most scenic drives in the USA.

Gimmie a ”V”! . . . Or is that “U”? . . .
The valley shown in the photo is a great example of a “glacial trough” sculpted by an alpine glacier that flowed though here during the last ice age over 10,000 years ago. Valleys carved by rivers in mountainous areas tend to have distinct V-shapes, whereas those shaped by glaciers tend to be U-shaped. During the ice ages glaciers formed in Montana’s high mountainous areas near the upper portions of river basins and then flowed down through river valleys. Along the way the glaciers plucked rock material from the valley walls, widening and re-shaping them as they plowed through.

Where melting equals movement. . .
Eventually, as these glaciers flowed out of the mountains they reached elevations where they began to melt back as fast as they were flowing downward. While the climate was stable, the front (toe) of the glacier stayed in one place for decades. As a result any rocks that were embedded in the ice and stuck to the bottom or the sides of the glacier were deposited there, forming a ridge of rock material called an end moraine. For the glacier that widened this valley the moraine is located about 12 miles north of Red Lodge. Since we are in what paleoclimatologists refer to as an interglacial period, a river (Rock Creek) once again occupies the U-shaped trough.

Don’t be in such a hurry!. . .
The Beartooth Scenic Highway, also known as (the Cooke City Highway”) is a drive that every Montanan should take. If you don’t stop, it takes bout 2.5 hours to get from Billings to Cooke City. But don’t hurry! Be sure to take several stops along the way, including the beautiful “scenic turnout” where this photo was taken from. The turnout has a nice parking lot, restrooms, and a walkway that offers breathtaking views of the valley below and the surrounding Beartooth Plateau. The short walkway is constructed primarily of gneiss, a rock formed as granite is changed by heat and/or pressure. To take the highway, turn south at Laurel and continue south through Red Lodge.

Terms: interglacial period, alpine


*Hanging Valleys?
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By Rod Benson
Earth Science Teacher at Helena High School

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