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VOLCANOES CH 10 Volcanoes 4 Factors affecting eruptions 1. Magma composition Basaltic – low silica and low viscosity Rhyolitic – high silica and high viscosity Andesitic – midway between the 2 2. Magma temperature = hotter flows easier 3. Magma viscosity – determined by temp and composition. High viscosity = violent eruptions 4. Dissolved gases = more gasses means more violenc 3 Volcanic Materials 1. Lava flows – 3 textures 1. Aa – rough and jagged 2. Pahoehoe - wrinkly and ropey texture 3. Pillow - forms underwater 2. Gases – water vapor, CO2, nitrogen, sulfur and chlorine 3. Pyroclastic materials – ejected fragments 3 SIZES 1. Ash – fine material 2. Cinders and lapilli – medium/pebble sized 3. Bombs and blocks – big stuff, block = hard, bombs = lava Aa LaVa on the left PAHOEHOE PILLOW LAVA BLOCK BOMB Volcanic Terms Crater – steep walled depression at top Conduit – pipe connecting magma chamber to the surface Vent – top of the conduit Caldera – large depression in a volcano due to collapse of volcano Volcanic neck – remnant of eroded volcano Columnar jointing – 6 sided columns from cooling magma Lava plateau – raised flat area of lava/fissure=crack Caldera = Crater Lake Volcanic Neck = Ship Rock Columnar Jointing Columnar Jointing = Devil’s Tower FISSURE ERUPTION 3 VOLCANO TYPES: 1. SHIELD CONE --broad base & gently sloped sides --huge size --mild eruptions --mostly lava flows --basaltic lava/oceanic usually --low in silica --example = Hawaii Shield Volcano = Hawaii 2. CINDER CONE --narrow base & steep sides --small size --violent eruptions for size --mostly tephra --granitic lava/continental usually --high in silica --example = Paricutin & Sunset Crater CINDER CONE 3. COMPOSITE CONE (Stratovolcano) --medium base & moderately sloped --medium size --both violent & mild --both lava flows & tephra --andesitic lava / found “near” coasts --medium amount of silica --example = Mt. St. Helens & Andes Composite/Strato--Volcano Mount Saint Helens Mount Saint Helens Extra-Terrestrial Vulcanism (3) 1. IO = moon of jupiter 2. Olympus Mons = huge hot spot shield volcano 3. Moon = has lava flows but NO volcanoes IO = moon of Jupiter Olympus Mons = Mars Volcano Marias on the Moon 3 Volcano Dangers 1. Pyroclastic flows – hot gases, glowing ash, and larger rock fragments Very hot Can attain 200 km/hr about 120 mph 2. Lahars – mudflow formed from volcanic ash and water (melted snow or rain) 3. Eruptions – you’re there one minute and gone the next… Pyroclastic Flow LAHAR Igneous Activity Plutons (intrusive igneous bodies) Classified by shape, size, and relationship to surrounding rock layers (5 types) Sill – horizontal and between rock layers Dike – vertical and cut across rock layers Laccolith – dome/mushroom shaped plutons Batholith – more than 100 km2 of exposed rock Stock – less than 100 km2 of exposed rock 3 Factors for Origin of Magma Read pages 291 – 292 1. The role of heat 2. The role of pressure 3. The role of water 3 Volcano Locations 1. Convergent plates Subducting plate melts and magma rises Japan and Mt St Helens 2. Divergent plates Plate diverge and magma rises through the rift Mid-ocean ridge Iceland East African Rift 3. Intraplate (hot spots) Mantle plume rises towards the surface Hawaii and Yellowstone