|
Yamsay Mountain is a large shield volcano in the Cascade Range of south-central Oregon, located about east of Crater Lake on the border between Klamath County and Lake County. It is part of the Cascade Volcanic Arc but is located in a mountain range behind the main Cascade volcanic front. The best known members of this enigmatic arc are the massive shields of Newberry Volcano, about farther north in Oregon, and Medicine Lake Volcano, about south in Northern California. Yamsay is the highest volcano in the eastern arc, almost higher than Newberry and Medicine Lake. A central part of Klamath mythology, the mountain offers activities such as hiking and horseback riding. Historically, the area around it has been inhabited by Native American tribes and settlers. Until the 1970s, a fire lookout tower sat on the summit of the mountain, and its foundation remains to this day. Life in the Cascades is quite diverse. The western half of the range features lush vegetation, and the eastern portion is drier. The range supports many animals, including both endemic and endangered species. == Geography and geology == Like other volcanoes in the Cascades Range, Yamsay was produced by subduction of the oceanic Juan de Fuca Plate under the North American Plate. Annual convergence between the two continues at a rate of per year. The Cascades make up the majority of the North American West Coast volcanoes; they have been volcanically active for about 36 million years. The rock making up the Cascades is slightly older, dated between 55 and 42 million years old. In an attempt to organize the volcanoes by age, scientists typically divide them into two provinces: the High Cascadesthe younger volcanoesand the Western Cascades, comprising the older volcanoes. Yamsay, along with the Simcoe volcanic complex, Medicine Lake Highlands, and Newberry Volcano, make up a wayward range of shield volcanoes between and east of the main Cascade Range. Volcanism at these centers is unlike other eruptions in the Cascades, and it does not stem from fissures as would Basin and Range volcanism. The volcanoes appear to be isolated from the major volcanic ranges in the Northwestern United States, although scientists group them as part of the Cascades. Recent volcanism in the Cascades, lasting from 7 to 2 mya, produced largely basaltic and basaltic andesite-based material (up to 50 percent). On the eastern side of the High Cascades, however, volcanoes erupted dacite, andesite, and rhyolite. These materials made up several types of eruptions: lava flows, domes, and pyroclastic flows. In the most recent volcanic activity, andesite, basalt, and rhyolite have been erupted from High Cascades volcanoes, particularly the Three Sisters, Broken Top, Mount Hood, Mount Jefferson, and Crater Lake. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Yamsay Mountain」の詳細全文を読む スポンサード リンク
|