Lacustrine geyserite sediments (West Thumb Geyser Basin, Yellowstone, Wyoming, USA) 3 : 無料・フリー素材/写真
Lacustrine geyserite sediments (West Thumb Geyser Basin, Yellowstone, Wyoming, USA) 3 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Lacustrine geyserite sediments in Wyoming, USA.Geyserite (a.k.a. siliceous sinter) is a rare, friable to solid, chemical sedimentary rock composed of opal (hydrous silica, a.k.a. opaline silica: SiO2•nH2O). Geyserite forms by precipitation of hydrous silica from hot spring or geyser water. At the Yellowstone Hotspot Volcano in Wyoming, the source of the silica is subsurface rhyolite lava flows of late Cenozoic age. Superheated groundwater moves along fractures in the rhyolite and leaches out silica. When hot spring or geyser water reaches the surface, the water cools and evaporates, resulting in precipitation of very thin layers of opal on any substrate. Numerous precipitation episodes (for example, from repeated geyser eruptions) results in the buildup of geyserite.The above photo shows geyserite sediments on the shores of Yellowstone Lake, a little above water level. Geyserite is a rare sediment type, but is moderately common in watercourses that run through Yellowstone's geyser basins and along lake margins in hydrothermal areas. The material here is derived from erosion and lacustrine reworking of an extensive geyserite/siliceous sinter platform. The sediments are moderately sorted, relatively coarse-grained, and angular to subangular. The grains appear to be dominated by small pebbles, granules, and coarse sand.The shoreline-parallel ridge of geyserite sediments formed by wave action when lake levels were higher than on the day the picture was taken. Yellowstone Lake's water level is relatively low before the spring snowmelt and rises noticeably during late spring and summer.Locality: southwestern shores of Yellowstone Lake's West Thumb, Lower Group, West Thumb Geyser Basin, Yellowstone Hotspot Volcano, northwestern Wyoming, USA |
| 撮影日 | 2012-12-13 16:00:00 |
| 撮影者 | James St. John |
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