Gypsum snowballs (Snowball Dining Room, Mammoth Cave, Kentucky, USA) 41 : 無料・フリー素材/写真
Gypsum snowballs (Snowball Dining Room, Mammoth Cave, Kentucky, USA) 41 / 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 | Cleaveland Avenue is a long tubular passage in western Kentucky's Mammoth Cave, the longest cave on Earth. As of March 2024, 426 miles of passages have been explored and mapped. When first discovered, Cleaveland Avenue had abundant, complex, large gypsum structures - some the size of celery stalks. Naturally-detached speleothem littered the floor. The passage has been intensely vandalized by thousands of guides and tourists over the decades. Moderately impressive gypsum speleothem still remains, such as gypsum coatings, crusts, flowers, and helictites. The original color of most of the gypsum speleothem was bright white. Almost all of it is now stained or highlighted with dark gray coloration - this is from decades of lantern smoke. Some gypsum is orangish-brown in color, due to minor iron oxide impurities.The sulfur in the gypsum is derived from pyrite in an overlying unit. Downward-percolating water oxidized the pyrite (FeS2 - iron sulfide - "fool's gold") and produced sulfuric acid (H2SO4). The acid dissolved part of the limestone, which liberated calcium (Ca). In the presence of water, the calcium and the sulfate (SO4) produced gypsum.Seen here are gypsum snowballs - irregularly hemispherical masses of gypsum. When first discovered, this site was likened to a place where boys had just engaged in a snowball fight. The gypsum was originally white. Some of the smoke staining was removed from these snowballs during a long, careful cleaning project conducted by Mammoth Cave Park. Pristine, bright white gypsum snowballs are present in non-vandalized parts of the Mammoth Cave system (e.g., Turner Avenue - see: www.flickr.com/photos/jsjgeology/8321107667).Cleaveland Avenue is at Level C in the Mammoth Cave system. Level C passages started forming about 1.9 million years ago. A subterranean river used to flow through the passage.The bedrock substrate is part of the Joppa Member of the Ste. Genevieve Limestone (Middle Mississippian).Locality: ceiling of Snowball Dining Room, Cleaveland Avenue (near the intersection with Marion Avenue), Mammoth Cave, west-central Kentucky, USA----------------------------------(accessed with park permission) |
| 撮影日 | 2024-03-11 14:43:17 |
| 撮影者 | James St. John |
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