Natural Bridge of Virginia (Natural Bridge State Park, Virginia, USA) 2 : 無料・フリー素材/写真
Natural Bridge of Virginia (Natural Bridge State Park, Virginia, USA) 2 / 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 | Natural bridge developed in Ordovician dolostones and limestones in Virginia, USA.Rock arches are rare erosional features. Rock arches that are not formed by river or stream erosion are called "natural arches". Those that are formed by river or stream erosion are called "natural bridges". Natural bridges are rarer than natural arches. The highest concentration of natural arches on Earth is Arches National Park in eastern Utah, USA. Very small erosional openings in rocks are called windows. Larger erosional openings are arches.Shown above is a natural bridge in Virginia, USA. The rocks are Ordovician-aged carbonates. The arch itself is composed of dolostone with floating quartz sand grains. This unit is mapped as the lower part of the Beekmantown Formation (Lower Ordovician) by Spencer (1968). The cliffs below the span are marine, sparsely-fossiliferous limestones of the upper Chepultepec Formation (Lower Ordovician).Natural Bridge of Virginia is hypothesized to have formed by roof collapse of a large cave passage containing an underground river.This rock arch is ~215 feet high, ~40 feet in vertical thickness, ~100 feet in lateral width, and has a ~90 feet span between the underlying cliff walls.Locality: Natural Bridge State Park, southern Rockbridge County, west-central Virginia, USA-------------------Geologic info. from:Spencer (1968) - Geology of the Natural Bridge, Sugarloaf Mountain, Buchanan, and Arnold Valley Quadrangles, Virginia. Virginia Division of Mineral Resources Report of Investigations 13. 55 pp. 4 pls. |
| 撮影日 | 2016-05-13 17:25:32 |
| 撮影者 | James St. John |
| タグ | |
| 撮影地 |