150Lec19-1 - Lecture#19 Volcanism in the Pacific and...

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Lecture #19: Volcanism in the Pacific and Antarctica (Abbott, p. 208-209, 231-232, 234, 237-238, 241, 309-310) Know the countries of location of all bolded volcanoes in these notes. ___________________________________ _ Island Arc Volcanoes of the Pacific Ocean Location : Aleutian Islands of Alaska (USA), Japan ( Mt. Fuji and Mt. Unzen ), Philippines ( Mt. Pinatubo ), and Indonesia ( Mt. Tambora , Toba Caldera and Krakatau ). Be able to locate the Aleutian Islands and these countries on a map. Don't worry about the exact locations of the volcanoes, but know what countries they're in. Type: Stratovolcanoes and calderas Composition: Mostly mafic to intermediate (andesite) stratovolcanoes and felsic calderas Association: Mostly ocean-ocean plate convergence (Figure 3.17, p. 63) ___________________________________ Introduction: Ocean-Ocean Convergence Zones in the Pacific As mentioned earlier, island arc volcanoes are largely associated with the convergence of two oceanic plates (Figure 3.15, p. 61). The older plate tends to be colder and denser, and subducts under the younger, warmer and less dense plate. The subduction zone is marked by a trench on the seafloor (Figure 3.2, p. 51). At depths of about 50-100 kilometers into the Earth, the subducting plate melts beginning with any wet silica-rich ocean sediments that may be trapped within the plate. Water is also readily released from the subducting plate. The water rises and partially melts peridotite in the mantle overlying the plate. The partially melted ultramafic peridotite produces mafic magmas. As the mafic magmas rise towards the surface, they may partially melt the overlying non- subducted oceanic plate, which would increase the silica content of the magma and possibly transform it from mafic to intermediate. Magma Production in Ocean-Ocean Convergence Zones:
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Aleutian Islands and Alaska Peninsula, Alaska The Aleutians are an island arc off the southwest coast of the Alaskan mainland. The Aleutian Island stratovolcanoes result from the subduction of the oceanic Pacific plate under oceanic portions of the North American plate (Figure 3.24, p. 68; Figure 3.3, p. 52). Augustine and Redoubt are two stratovolcanoes on the nearby Alaska Peninsula. Augustine volcano erupted in 2006. Redoubt volcano also has been recently active. Redoubt volcano is located to the southwest of the city of Anchorage and Augustine is nearby. Mt. Pinatubo, Philippines
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150Lec19-1 - Lecture#19 Volcanism in the Pacific and...

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