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VOLCANISM 80% of the earths crust is composed of volcanic rocks

VOLCANISM 80% of the earths crust is composed of volcanic rocks Volcanism: the process by which magma from the interior of the earth rises through the crust, emerges onto the surface as lava, and cools into volcanic rock. Anatomy of a volcano. Types of lava (based on silica content)

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VOLCANISM 80% of the earths crust is composed of volcanic rocks

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  1. VOLCANISM • 80% of the earths crust is composed of volcanic rocks • Volcanism: the process by which magma from the interior of the earth rises through the crust, emerges onto the surface as lava, and cools into volcanic rock

  2. Anatomy of a volcano

  3. Types of lava (based on silica content) • felsic, andesitic, mafic • Types of Volcanic Deposits • Basaltic: Flood Basalts Different Layers of Basalt

  4. Types of Volcanic Deposits (cont) • Basaltic: Pahoehoe, • Aa, • Pillow lava • Rhyolitic • Andesitic

  5. Textures glassy, vesicular (related to cooling rates and gas content)

  6. Explosive vs. Gentle Eruptions

  7. Explosive vs. Gentle Eruptions • Pyroclastic Deposits • Air fall or tephra • Ejecta: ash, tuffs and breccias, bombs

  8. Pyroclastic Flows • Surge – directed blast of hot material • nuée ardante (glowing cloud) • Mudflow • lahar

  9. Landforms and Eruptive Styles 1. Shield Volcanoes i. gentle eruptions consisting of basaltic lavas ii. low silica and low viscosity iii. fissure eruptions and flood basalts iv. example: Mauna Loa

  10. Volcanic Domes i. explosive eruptions consisting of felsic volcanism ii. high silica and high viscosity iii. ash flows iv. example: Mount St. Helens (1980)

  11. Cinder-Cones Volcanoes i. pyroclastic eruptions

  12. Composite Volcanoes (stratovolcano) i. alternating lava and pyroclastic eruptions

  13. Craters i. central depression at the summit of most volcanoes Calderas (collapsed craters)

  14. Other Volcanic Features 1. diatremes 2. fumaroles, hot springs, geysers

  15. Plate Tectonics and Volcanism

  16. Plate Tectonics and Volcanism (cont) • 1. Spreading zone volcanism: basalts • 2. Convergence zone volcanism: Ring of Fire • i. OC-OC convergence: basalts and occasional andesites • ii. OC-CC convergence: ash and rhyolite • 3. Interplate volcanism • 4. Hot Spot Activity

  17. Benefits of Volcanism • atmosphere, oceans, land masses, soil, geothermal uses

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