Mount Thielsen Volcano (Cascade Range, Oregon, USA) 2 : 無料・フリー素材/写真
Mount Thielsen Volcano (Cascade Range, Oregon, 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 |
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| 説明 | Mount Thielsen is an apparently extinct volcano in the Cascade Range, a north-south linear chain of otherwise active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera.------------------------------From roadside overlook signage near Mount Thielsen:Mt. Thielsen [is] a relatively small, steep-sided composite cone built atop a complex of older, gently sloping shield volcanoes. The deeply eroded upper flanks of the volcano are formed chiefly of sloping layers of explosively ejected ash, cinders, and rock fragments consolidated into colorful beds of tuff and coarse volcanic breccia. A few lava flows are sandwiched between the beds of eruptive debris.Lavas analyzed from Mt. Thielsen indicate that the volcano probably began to form around 300,000 years ago. Because its summit and flanks are so deeply gouged, geologists infer that the volcano likely experienced multiple episodes of glaciation. The advanced degree of erosion suggests that Mt. Thielsen is no longer active. Its jagged pinnacle is a volcanic plug formed of dense basalt that attracts countless thunderbolts. Mt. Thielsen has come to be known as the "Lightning rod of the Cascades".------------------------------Locality: Mount Thielsen (as seen from Crater Lake National Park), on the Umpqua National Forest-Winema National Forest border, east of Diamond Lake & north of Crater Lake, Klamath County-Douglas County border area, southwestern Oregon, USA------------------------------See info. at:en.wikipedia.org/wiki/Mount_Thielsen |
| 撮影日 | 2012-08-04 15:42:04 |
| 撮影者 | James St. John |
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