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| The above image shows the extreme western edge of the Columbia Plateau. This is a plateau of Miocene Basalt that covers Idaho, Washington, Nevada, and California....about 175,000 sq. miles making this larger in size than the 60,000 sq. mile Antrim lava plateau of Greenland and Iceland. Lava has been deposited here to depths of 5000 feet. The above picture shows various flows exposed on the western edge of the plateau near Crescent Bar, Washington about 10 miles west of Quincy, WA. This area is directly along the Columbia River and was gouged out and carved in much more recent years (10 to 15,000 years ago) by massive flooding. (also see: Waterville) |
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| Basalt columns near Rock Island Dam on the Columbia. Basalt can vary from very dark gray to almost black. In wet regions it turns a rust while in dry areas it can become white and limy. The flood basalts of the Columbia Plateau were very fluid. When they were erupting from massive cracks in the ground, they could flood the region with hundreds of miles of lava in a very short period of time. Basalt consists of about half feldspar and half ferro-magnesian minerals. The fluid nature of this lava does not produce volcanic mountains but rather smooth layers of flows. As a layer cools it may joint and crack into prismatic shaped columns. |
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For More information on the Columbia Plateau see the publication: The Channeled Scablands published by the U.S.G.S. Harlan Bretz was the geologist that proposed that the Columbia was deluged with massive floods when the ice sheets began to melt. Also see: http://volcanoes.usgs.gov/Products/Pglossary/basalt.html |