Columnar-jointed basalt (Columbia River Flood Basalt, Miocene, ~15-17 Ma; Mud Hollow, Oregon, USA) 9 : 無料・フリー素材/写真
Columnar-jointed basalt (Columbia River Flood Basalt, Miocene, ~15-17 Ma; Mud Hollow, Oregon, USA) 9 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
|---|---|
| 説明 | Columnar-jointed basalt in the Miocene of Oregon, USA.The vertical fractures seen here are columnar jointing. With cooling, many lava flows contract slightly after they solidify. Contraction results in the formation of polygonal columns - columnar jointing. As seen from above, the columns often have a hexagonal or pentagonal shape, but other shapes are known. Some famous examples include Devils Tower in Wyoming, Devil's Postpile in California, and Giant's Causeway in Ireland.The basalt lava flow seen here is part of the Columbia River Flood Basalt of Miocene age. Flood basalts are vast outpourings of lava from one or more large fractures in the crust. This rare type of volcanism is not occurring on Earth at present, but there are ancient flood basalt provinces that can be examined - for example, the latest Cretaceous-aged Deccan Traps of India and the latest Permian Siberian Traps of Russia. Flood lavas are also known on Mercury, Venus, and the Moon.Most of the Columbia River Flood Basalt erupted over a time span of a little over one million years, between 15 and 17 million years ago, during the Miocene. The deposit has been partially eroded, but covers much of Washington State and Oregon, plus parts of Idaho. Some lava reached the Pacific Ocean.The cause of the Columbia River Flood Basalt volcanism is not entirely settled, but is probably related to the initial emergence of the Yellowstone Hotspot mantle plume in the late Tertiary. Since it first appeared, the Yellowstone Hotspot has been moving ~eastward from the Oregon-California-Nevada area and is currently in northwestern Wyoming. In reality, the North American Plate is moving over the Yellowstone Hotspot.Locality: roadcut along Mud Hollow Road, south-southeast of the town of Biggs Junction, far-northern Oregon, USA--------------------------------Info. at:www.usgs.gov/observatories/cvo/columbia-river-basalt-grou...anden.wikipedia.org/wiki/Columbia_River_Basalt_Group |
| 撮影日 | 2012-08-01 13:46:26 |
| 撮影者 | James St. John |
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