30 Aug '14, 11pm

Contour Plowing in the Palouse: By planting in narrow strips and plowing in patterns that mimic the natural co...

The next time you fly over southeastern Washington, look down. The expanse of undulating hills covering the landscape is one of the more beautiful—and geologically distinctive—in the United States. In comparison to the long, linear ridges in many areas, the hills in the Palouse are arranged in a complex web of interlacing humps and hollows that look almost randomly placed. Tectonic forces did not push up these hills, nor did rivers carve away valleys to create them. Instead, it was the wind. During the last Ice Age, winds blew in fine-grained silt, or loess, from the southwest. Much of it was rock flour, which had formed as glaciers crushed bits of rock along the land surface. As winds transported and sculpted loess into distinctive dunes, a layer of silty soil—best known for its rich mineral content and ability to retain moisture—formed on their surfaces. Since the Palous...

Full article: http://earthobservatory.nasa.gov/IOTD/view.php?id=84263&s...

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