Travertine stalactites in Great Onyx Cave (Flint Ridge, Mammoth Cave National Park, Kentucky, USA) 5 : 無料・フリー素材/写真
Travertine stalactites in Great Onyx Cave (Flint Ridge, Mammoth Cave National Park, Kentucky, USA) 5 / 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 | Travertine stalactites (dripstone) in Great Onyx Cave.Great Onyx Cave is located in the northern part of Flint Ridge in Mammoth Cave National Park, Kentucky, USA. It has 8 miles worth of mapped passages. Geologically, Great Onyx Cave is part of the Mammoth Cave System, but it has become erosively separated from it (although an air flow connection with the Mammoth Cave System has been identified). Great Onyx Cave is the downstream continuation of the Salt Cave section of the system.The walls of Great Onyx Cave are limestones of the Paoli Member, shales of the Bethel Member, and limestones of the Beaver Bend Member of the Girkin Formation (lower Upper Mississippian). The travertine speleothem-rich areas of Great Onyx Cave are wet and occur where a cap of overlying Big Clifty Sandstone is absent. The dry portions of the cave are below an intact Big Clifty Sandstone "caprock", and include the giant canyon passage areas and the gypsum speleothem areas.The main cave passage of Great Onyx Cave is called Edwards Avenue. It is a giant canyon passage at Level B in the Mammoth Cave System. Level B passages formed about 2 to 4 million years ago during the Pliocene.This cave is sometimes accessible to the general public by guided lantern tours during boreal summer months. This photo was taken during a field trip in June 2011 as part of a cave geology course at Mammoth Cave park."Speleothem" is the technical term for "cave formations", and refers to all secondary mineral deposits in caves. The most common speleothem-forming mineral is calcite (CaCO3 - calcium carbonate), the same mineral in limestone, which is the host rock for almost all caves on Earth. Speleothem composed of calcium carbonate is given the compositional rock name travertine. Some travertine forms at the surface, at hot springs or cold springs. Cave travertine forms in many specific ways, and genetic rock names have been established for the many known varieties (e.g., dripstone, flowstone, helictites, coralloids, shelfstone, rimstone, etc.).The stalactites shown above are a variety of travertine speleothem called dripstone, which forms by dripping water. Stalactites are vertically-oriented dripstones attached to cave ceilings or upper slanted walls. Rapid dripping produces relatively small stalactites. Slow dripping produces relatively large specimens. Notice that all of the small foreground and midground stalactites are aligned - this is the result of water percolating downward into the cave via narrow fractures (joints). The larger stalactites in the background (bottom part of photo) are also joint-aligned.The larger structure at bottom center is a travertine column, a variety of dripstone formed by the fusion of a stalactite with a stalagmite (growing upward from a cave floor). |
| 撮影日 | 2011-06-16 14:26:53 |
| 撮影者 | James St. John |
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