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Volcanoes

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  • 1. V OLCANOES
  • 2. V OLCANOES Weak spots in the crust where magma (molten material) comes up to the surface. Most are found over the subduction zones. The word volcano comes from the Roman god of fire, Vulcan.
  • 3. M AGMA
  • 4. FACTORS That determine volcanic erruption 1. Magma’s temperature 2. Magma’s composition 3. Dissolved gasses
  • 5. M AGMA TYPESComposition Silica content Viscosity Gas Content Tendency to Volcanic form Landforms pyroclasticsBasaltic Least Least Least Least Shield dome, 50% 1-2% Basalt platform, Cinder conesAndesitic Intermediate Intermediate Intermediate Intermediate Composite 60% 3-4% conesRhyolitic Most Greatest Greatest Greatest Volcanic 70% 4.1-6% domes, Pyroclastic flows
  • 6. M AGMA’ S C OMPOSITION Basaltic  Tends to be fluid  Can travel a distance of 150km from the crater Andesitic  Volcanic roc composition is in between Basaltic and Rhyolitic. Rhyolitic  Very viscous  Tends to create stream-like ribbon flows
  • 7. O THER C OMPONENTS Magma’s Temperature  High – Fluid magma  Low – Viscous magma Dissolved gasses 75% - Water, 15% - Carbon Dioxide, 10% - other gasses Silica Content  Poor – More fluid, Gasses can escape easily  Rich – Traps gasses which may lead to explosive erruptions
  • 8. E XTRUDED M ATERIALS Lava  Magma without trapped gas  Comes from basaltic magma due to low silica content Gasses Pyroclastics  High silica content magma that forms from pulverized rock.
  • 9. C ONTINUATION Ash ~ Formed when lava contains many bubbles Pumice ~ Froth like structure Lapilli ~ Walnut sized Cinder ~ Pea sized Blocks ~ Bigger than lapilli, Made from hardened lava Bombs ~ incandescent (glowing) lava
  • 10. V OLCANO T YPES
  • 11. S HIELD Built from Basaltic magma Broad dome shape Example  Mauna Loa
  • 12. C INDER C ONE Very steep, small (300m) Made from pyroclastics Collapses easily
  • 13. C OMPOSITE Large, nearly symmetrical Made up of interbedded layers of lava and pyroclasts Examples  Mt. Mayon  Mt. St. Hellens

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