chapter 5 volcanoes
chapter 5 volcanoes GEOL 110
Long Beach State
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This 3 page Class Notes was uploaded by Elizabeth Rubio on Wednesday February 24, 2016. The Class Notes belongs to GEOL 110 at California State University Long Beach taught by Ewa Burchard in Spring 2016. Since its upload, it has received 22 views. For similar materials see Natural Disasters in Geology at California State University Long Beach.
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Date Created: 02/24/16
Chapter 5 Volcanoes Eyjafjallajökull 2010 Eruption Iceland home to more than 30 active volcanoes • Volcanic eruption in April 2010 – Ash plume 9.5 km (~6 mi) high – Caused shutdown of airspace throughout Europe • Largest aerial closure since WWII – Increased seismic activity in December 2009 • Future eruptions – 2010 eruption was small taste of what could happen if the more explosive Katla erupts Eyjafjallajökull icelandic mountain glacier eruption cause megafloods 5.1 Introduction to Volcanism Volcanic activity is directly related to plate tectonics – Most volcanoes are near plate boundaries – Approximately 2/3 of active volcanoes within “Ring of Fire” • At plate boundaries, magma is created – Magma is molten rock – Lava is magma on the Earth’s surface – Volcanoes form around a vent • Not all volcanoes are the same – Different processes in formation – Depends on tectonic settings How and where Magma forms? Most magma come from the asthenosphere Weak layer of rock that is close to melting temperature 3 Principal magma generating processes 1. Decompression melting Pressure exerted on hot rock is decreased Divergent plate boundaries, continental rifts, and hot spots 2. Addition of volatiles Chemical compounds that lower the melting temperature of the rock Subduction zones responsible for “RING OF FIRE” 3. Addition to heat Induces melting if temperature exceeds melting temperature Continental hot spots Magma Properties Described by silica content and amount of dissolved gasses • Three types of magma based on silica content (low to high) – Basaltic, andesitic, and rhyolitic • Magma less dense than surrounding rock – Rises toward the surface – Accumulates in magma chambers – Composition changes • Viscosity • Volatile content cont. Viscosity – Resistance to flow – Affected by temperature and composition • As magma cools, viscosity increases • As silica content increases, viscosity increases Affects The flow of lava Shape of resulting volcano Correlated to the volatile content Volcano types, formation and Eruptive, behavior, cont. Lava Domes Small dome with steep sides, it takes months to grow domes (by the magma pushing it) • Often form in the vent of a stratovolcano after an explosive eruption • Can grow in single event or over decades – Made from highly viscous magma • Exhibit highly explosive eruptions – Common in the “Ring of Fire” • Examples: Mount Lassen in CA, Mt. Unzen dome in Japan cont. Volcanoes vary greatly – Size, shape, composition – Number of eruptions in formation – How and where magma is formed – Amount of magma evolution – Volatile content • Viscosity and volatile content still primary control of eruption explosiveness – Volcanic explosivity index (VEI) • Relative scale to compare explosions cont. Shield Volcanoes – Largest volcanoes in the world • Thin lava flows build up volcano with gentle slopes • Wider than they are tall • Still among tallest mountains on Earth (measured from bases) – Associated with basaltic magma • Low viscosity, low volatile content • Gently flowing lava with nonexplosive eruptions • Develop a cladera – Common at hot spots in the oceanic lithosphere and divergent plate boundaries, continental rifts • Hawaiian Islands, Iceland, and in the East African Rift • Examples: Mauna Loa and Kilauea in Hawaii cont. Stratovolcanoes – Known for beautiful conical shapes • Result of high viscosity magma • Lava does not flow far resulting in steep sides – Mixture of explosive activity and lava flows • Produce combination of lava flows and pyroclastic deposits • Also called composite cones – Can be extremely explosive • Responsible for over 80% of eruptions • Responsible for most of the death and destruction – Common in the “Ring of Fire” • Examples: Mount St. Helens and Mount Rainer in United States, Mount Fuji in Japan
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