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

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

10. 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

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

14. Cinder-Cones Volcanoes i.pyroclastic eruptions

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

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

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

21. Plate Tectonics and Volcanism

22. 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

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