Volcanoes

Volcanoes - Volcanoes Volcanoes are the more-or-less...

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Volcanoes Volcanoes are the more-or-less cone-shaped surface accumulations of molten rock (lava) and its pyroclastic equivalents. They vary widely in appearance, composition, and behavior Volcano Varieties o Shield volcano (basalt) o Stratovolcano (andesite) o Plug dome (rhyolite) o Cinder cone (basalt fragments) Active Volcanoes (exclusive of those on spreading ridges) o Pacific Ring of Fire o Hot Spots The Magma responsible for volcanoes is formed by the partial melting of rocks in the crust and mantle in a variety of geologic and tectonic settings: 1) Below mid ocean ridges 2) In mantle plumes 3) Above some subduction zones 4) In zones of mountain building Where does melting occur? 1) Magmatism at mid-ocean ridges Melting is a result of decompression of asthenospheric mantle rock (peridotite) rising beneath ridges Occurs at 30-60 km depth As asthenosphere flows upward beneath the mid ocean ridges, it undergoes a higher degree of partial melting because confining pressure (which inhibits melting) is reduced. East African Rift system, Afar Triangle, Red Sea, Atlantic Ocean Erte Ala caldera 2) Beneath “hot spots” and within so-called mantle plumes a. Hot spots are areas on the planet where magmatic activity has been identified
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This note was uploaded on 10/05/2008 for the course GEOL 105Lg taught by Professor Davis,platt during the Fall '07 term at USC.

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Volcanoes - Volcanoes Volcanoes are the more-or-less...

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