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El Valle is a stratovolcano in central Panama and is the easternmost volcano along the Central American Volcanic Arc which has been formed by the subduction of the Nazca Plate below Central America. Some time prior to 200,000 years ago, the volcano underwent a huge eruption event that caused the top of the volcano to collapse into the empty magma chamber below forming a large caldera. Several lava domes have developed inside the caldera since the collapse—forming Cerro Pajita, Cerro Gaital and Cerro Caracoral peaks. Prior to research in the early 1990s, it was thought that no active volcanism existed within Panama. But radioactive dates from El Valle show that the volcano last erupted as recently as 200,000 years ago.〔Defant, M. J., Clark, L. F., Stewart, R. H., Drummond, M. S., de Boer, J. Z., Maury, R. C., Bellon, H., Jackson, T. E., and Restrepo, J. F., 1991, Andesite and dacite genesis via contrasting processes: the geology and geochemistry of El Valle Volcano, Panama: Contrib. Mineral. Petrol., v. 106, p. 309-324〕 Work by de Boer et al.〔de Boer, J., Defant, M.J., Stewart R. H., Restrepo, J. F., Clark, L. F., and Ramierez A. H., 1988, Quaternary calc-alkaline volcanism in western Panama: Regional variation and implication for the plate tectonic framework: J. South American Earth Sciences, v. 1, p. 275-293.〕 and Defant et al.〔Defant, M. J., Richerson, P.M., de Boer, J. Z., Stewart, R. H., Maury, R. C., Bellon, H., Drummond, M. S., Feiganson, M. D., and Jackson, T. E., 1991, Dacite genesis via slab melting and differentiation: La Yeguada Volcanic Complex, Panama, J. Petrol., v. 32, p. 1101-1142.〕〔Defant, M. J., Jackson, T. E., Drummond, M. S., de Boer, J. Z., Bellon, H., Feigenson, M. D., Maury, R. C., and Stewart, R.H., 1992, The geochemistry of young volcanism throughout western Panama and southeastern Costa Rica: An overview: J. Geol. Soc. Lond., v. 149, p. 569-579.〕 of other volcanoes within Panama have shown that there are two episodes of volcanism—young (< 2.5 million years ago) and old (> 4.5 million years ago) groups. The young volcanism consists of adakites (slab melts) whereas the older volcanism appears to be normal calc-alkaline volcanism. ==See also== *List of volcanoes in Panama *El Valle de Antón, a nearby town * APROVACA 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「El Valle (volcano)」の詳細全文を読む スポンサード リンク
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