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Tuesday, November 9th, 2010 • Learning Targets – Describe how plate tectonics influence the formation of volcanoes – Identify the parts of a volcano – Locate major zones of a volcano • Homework – Ch. 18.1 LTs due tomorrow • Q.O.D – What are volcanoes? Plate Tectonics and Volcanoes Earth Science Chapter 18 Volcanoes • What are volcanoes? – Opening in Earth’s crust through which molten rock, gases, and ash erupt and the landform that develops around this opening. Zones of Volcanoes Convergent Volcanism• Most volcanoes located on land result from ocean-continental subduction • Explosive eruptions • 2 major belts– Circum-Pacific Belt (Ring of Fire)-outlines west coasts of NA, SA, Aleutian Islands, east coast of Asia – Mediterranean Belt- outlines boundaries between Eurasian, African, Arabian plates Zones of Volcanism Divergent Volcanism-magma rises to fill in ocean gap. • Occurs at ocean ridges. • Non-explosive, large amounts of lava. • 2/3 of volcanism occurs underwater at divergent boundaries. Zones of Volcanism • Hot spots-Occur far from boundaries, high temperature plumes of magma. • Plumes stay stationary but the plates move • Forms a chain of volcanoes Hot Spots • What is Magma – Molten rock that is below the surface of the earth – Located in the mantle – Forms when rocks melt due to subduction • What is Lava – Molten rock that has reached the surface of the earth – Forms when volcanoes erupt • What is magma/lava made of? – Silica – Water – Magnesium – Iron • What are the different types of magma/lava? – Granitic (Felsic) • Made of 70% or more silica • High viscosity – Basaltic (Mafic) • Made of 50 % or less silica • Low viscosity • What does granitic(Felsic) magma look like? – Light in color – Contains a lot of water – Does not flow easily – Highly viscous – Often solidifies before reaching the earth’s surface • What does basaltic (mafic) magma look like? – Dark in color – Flows easily – Does not contain a lot of water • What are the different kinds of eruptions? – Pyroclastic-Convergent with Subduction • Highly explosive • Felsic • Lots of “stuff”- Organized by size – Bombs • Extremely large chunks erupted from volcano – Lampilli • Smaller than bombs – Ash • Fine grained/very small chunks • Non-Pyroclastic- Divergent – Non-explosive – Mafic lava – Mid-Atlantic Ridge is best example – Hawaii Islands • What are the different types of volcanoes? – Shield cone • • • • Broad or wide Not very tall Mellow eruptions Hawaii – Cinder cone • • • • Narrow Tall Pyroclastic eruptions Mexico City – Composite Cone • Alternating layer of lava and cinders (ash) • Alternates pyroclastic and non-pyroclastic eruptions • Mount St. Helens Plutonic Activity – Solidification of magma in the earths crust – Hardens in any existing rock – Types • Batholiths – Magma exposed at the earth’s surface – Largest – Exposed at the surface due to erosion • Stock – Magma exposed at the earth’s surface – Smaller than batholiths – Exposed due to erosion • Dike – Magma cools inside a fracture (break in the crust with no movement) – Cut across vertically • Sill – Magma goes into rock layers horizontally • Laccolith – Magma goes into rock layers horizontally – Hardens and makes a dome like structure Plutonic Activity Ring of Fire Mafic Lava Felsic Lava Stages of Cinder Cone Cinder Cone Sunset Crater Composite Cone Mt Fuji, Japan Shield Cone Galapagos Islands Volcanoes