Columnar-jointed trachybasalt (Postpile Flow, Upper Pleistocene, 82 ka; Devils Postpile National Monument, eastern California, USA) 73 : 無料・フリー素材/写真
Columnar-jointed trachybasalt (Postpile Flow, Upper Pleistocene, 82 ka; Devils Postpile National Monument, eastern California, USA) 73 / 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 | Trachybasalt in the Pleistocene of California, USA.Famous localities for seeing excellent columnar jointing include Giants Causeway (Ireland), Devils Tower (Wyoming, USA), and Devils Postpile (California, USA). Columnar jointing forms as a lava flow cools and contracts, resulting in the development of shrinkage cracks. As shrinkage cracks grow, they branch at ~120º angles (as seen in plan view). Crack networks merge with other networks to form columns having a polygonal cross-section shape. Most columns are hexagonal or pentagonal in shape. A few are 3-sided, 4-sided, or 7-sided.Devils Postpile is a trachybasalt (or basaltic trachyandesite) lava flow with well-developed columnar jointing. Erosion has toppled many of the columns into a large pile at the base of the flow. The flow represents part of the activity of the Long Valley Volcano, which is now a large caldera in the eastern Sierra Nevada Mountains of California. The Devils Postpile lava flow erupted outside the southwestern margin of the Long Valley Caldera.Stratigraphy: Postpile Flow, Upper Pleistocene, 82 kaLocality: Devils Postpile National Monument, west of town of Mammoth Lakes, eastern California, USA---------------Info. synthesized from:Huber et al. (2001) - The Story of Devils Postpile, a Land of Volcanic Fire, Glacial Ice and an Ancient River, Updated from the Original Edition.Bailey (2004) - United States Geological Survey Professional Paper 1692.Mahood et al. (2010) - Geological Society of America Bulletin 122: 396-407. |
| 撮影日 | 2010-07-07 21:58:59 |
| 撮影者 | James St. John |
| タグ | |
| 撮影地 |