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VOLCANOES AND VOLCANIC ERUPTIONS (Chapter 6)

VOLCANOES AND VOLCANIC ERUPTIONS (Chapter 6). A volcano produces. Lava flow (molten rock) Pyroclastic debris (solid chunks of rocks and ash) Volcanic gas and AEROSOLS (when volcanic gases condense to form tiny liquid droplets).

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VOLCANOES AND VOLCANIC ERUPTIONS (Chapter 6)

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  1. VOLCANOES AND VOLCANIC ERUPTIONS(Chapter 6)

  2. A volcano produces • Lava flow (molten rock) • Pyroclastic debris (solid chunks of rocks and ash) • Volcanic gas and AEROSOLS (when volcanic gases condense to form tiny liquid droplets)

  3. Ash, gas and aerosols combine to form the “smoke” above a volcano Volcanic behavior depends on: • VISCOSITY ("stickiness") of the magma • GAS CONTENT • TEMPERATURE

  4. More viscous (less fluid) magmas cause more explosive eruptions (Text page 176, table 6.2) Gases cannot easily escape from viscous magmas High pressure Explosive eruptions

  5. Viscosity of magma depends on: • Composition of the magma (how much silica it contains) This is the major factor that controls viscosity and explosivity of volcanoes • Temperature (Hotter magmas are more fluid)

  6. Volcanoes along mid-ocean ridges (e.g. Iceland) and hot spots (e.g. Hawaii) produce BASALTIC magma (pages 179-180) Basaltic magma is less viscous (low silica content, ~50%) and least dangerous It usually forms shield volcanoes (table 6.2)

  7. When Basaltic magma rises through continental crust, it melts the crustal rocks and form FELSIC (or rhyolitic) magma (silica >70%) Felsic magma is highly viscous and usually forms volcanic domes (table 6.2) This type of magma causes highly explosive eruptions

  8. Mixing of felsic and Basaltic magma, as well as melting of ocean sediments produces intermediate magma (ANDESITE, silica ~55%) Intermediate magma is most common in subduction zones and form composite volcanoes (or stratovolcanoes, table 6.2) Intermediate magma is highly explosive

  9. IMPACTS OF VOLCANIC ERUPTIONS Lava flows (Page 185) • Non-explosive, gentle eruptions • Will burn anything on its path • Is possible to control/divert lava flows (page 186)

  10. Pyroclastic flows (Page 186) • Mixture of HOT, mostly poisonous gases, ash and rocks • Can travel at speeds of 100-300 kmph (60-90 mph) • Can cover a large area in a very short time • Causes instant death on contact, flatten buildings and forests (e.g. Mt. St. Helens)

  11. Ash falls (Page 187) • Hot burning ash is fatal close to the volcano (e.g. Pompeii) • Windborne ash can cause respiratory problems, bury crops and spread toxic chemicals over large areas • Hazard to airplanes • Ash, dust and aerosols in the stratosphere can cause global cooling (similar to nuclear winter)

  12. Gases (pages 188-189) • Toxic sulfurous gases are harmful • Carbon dioxide can cause suffocation (e.g. Lake Nyos, Cameroon, West Africa, Fig. 6.22) • Water vapor from volcanic eruptions started the hydrologic cycle on the earth

  13. SECONDARY IMPACTS • Landslides and lahars (page 190) • Earthquakes • Tsunamis

  14. WHY DO PEOPLE STILL LIKE TO LIVE NEAR VOLCANOES? • Nutrient-rich soil • View (Travel and tourism, outdoor activities) • Geothermal energy

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