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Transcript
Volcanoes Volcano Vocabulary – Magma: molten (liquidy) rock, underground – Lava: Liquid rock that has escaped out of the ground, it is above ground – Crater: Circular hole near top of volcano, where Lava comes out – Tephra: Rock and hardened lava that pops/explodes out of volcano – Pyroclastic Flow: avalanche of hot rocks that flows on a cushion of intensely hot gasses. Travels up to 200 km/hr. – Viscosity: Resistance to flow High Viscosity = Thick, Slow flow Low Viscosity = Thin, Fast flow Why Volcanoes Erupt -Pressure builds as gases in Magma try to escape. -Enough pressure and Volcano erupts 3 Types of Lava –Basaltic: Low Silica, Low Viscosity, thin, flows easily. –Andestic: Medium Silica, Medium Viscosity. –Rhyolitic: High Silica, High Viscosity, thick, traps gasses creating violent eruptions. Shield Volcanoes • Basaltic lava – Lava oozes out – Gentle Eruption • Buildup of basaltic layers forms wide flat volcano • Layers of Cooled Lava • Ex.: Mauna Loa, HI • Found at weak spots in crust called “Hot Spots” Shield Volcano • \\A13-wins03\0300data\USERS\TEACHERS\CARLSTA\1. Earth Science\5. Volcanoes\Shield Cone Video.mov Cinder Cone Volcanoes Andesitic Lava Builds pressure and Lava pops out Lava cools in air making Tephra Piles of Tephra, Short with steep sides. Found At Fault lines like in Nevada and Arizona Tephra Pictures Cinder Cone Volcano • \\A13-wins03\0300data\USERS\TEACHERS\CARLSTA\1. Earth Science\5. Volcanoes\Cinder Cone Video.mov Composite Volcanoes • • • Rhyolitic Lava – High Pressure Forms giant Mountain-like Volcanoes Alternates between violent and non-violent eruptions: When high pressure = violent eruptions But, when the pressure is released, the next eruption will be non – violent (lava flow). • Has layers of tephra covered by lava • Occurs at Subduction Zones • Also known as a Stratovolcano – Ex. Mt. St. Helens, Soufriere Hills Composite Volcano • \\A13-wins03\0300data\USERS\TEACHERS\CARLSTA\1. Earth Science\5. Volcanoes\Composite Cone Video.mov