Travertine speleothem (Crystal Cave, Main Island, Bermuda) 7 : 無料・フリー素材/写真
Travertine speleothem (Crystal Cave, Main Island, Bermuda) 7 / 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 | (photo provided by Peri Forbes)---------------------------------------------Crystal Cave is one of over 100 caves known on the islands of Bermuda in the North Atlantic Ocean. Unlike the caves of the Bahamas, Bermuda's caves are generally not flank-margin caves, which are formed by aggressive dissolution of limestone in the fresh groundwater-salty groundwater mixing zone.Bermuda is a limestone-covered volcanic seamount. The igneous rocks of the seamount itself formed long ago at the Mid-Atlantic Ridge. Coral limestones and other limestone lithologies have since completely covered the seamount. During the Pleistocene Ice Age, global sea levels fluctuated considerably as continental glaciers advanced and retreated. Bermuda's limestone caves generally formed during times of relatively low sea level (= glacial intervals). Much travertine speleothem ("cave formations") formed after carbonate dissolution occurred - most of the speleothem crystallized in the old vadose zone (above the water table). Sea level now is higher (= interglacial interval), but not so high as to completely cover the Bermuda seamount. What used to be vadose speleothem is now, in many places, submerged in water. Karst exploration by divers has shown that many of Bermuda's caves are connected below the current water table.Locality: Crystal Cave, far-northeastern Main Island, Bermuda, northern Atlantic Ocean------------------------See info. at:en.wikipedia.org/wiki/Crystal_Cave,_Bermuda |
| 撮影日 | 2018-12-07 20:59:44 |
| 撮影者 | James St. John |
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