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Volcanoes Form as Molten Rock Erupts

Volcanoes Form as Molten Rock Erupts

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  • 1. Volcanoes Form as Molten Rock Erupts Pages 146-153 (section B)
  • 2. What is a Volcano?
    • Volcano - an opening in the Earth’s crust through which molten rock, rock fragments, and hot gasses erupt.
      • A mountain built up from erupted material is also called a volcano.
  • 3. What happens when a volcano erupts?
    • Volcanoes may erupt violently or gently
    • Even if no magma reaches the surfaces volcanoes can be dangerous
      • Hot rocks can fly out starting fires
      • Rocks can land on roofs in large numbers causing the roofs to collapse
  • 4. Magma
    • Magma contains silica and gases
    • Magma HIGH in silica is resistant to flowing
      • Causes violent eruptions
    • Magma LOW in silica flows easily
    • Magma rises as long as it is less dense than the surrounding rock.
    • When magma erupts it is called lava
  • 5. Volcanoes
  • 6. Volcanoes
  • 7. Rock Fragments
    • Fragments form as:
      • Escaping gas bubbles pop, tearing magma apart
      • Larger pieces of lava are thrown into the air, cooling and hardening during flight
      • Rocks of all sizes rip loose from volcanoes’ walls during eruptions
  • 8. Rock Fragments
    • Tiny rock fragments form volcanic ash , sized between dust fragments and grain of rice.
      • Stay in the air a long time, but travel far distances
    • Cinders are larger than ash, smaller than bombs
    • Bombs are the largest size rock fragments
      • Fall the fastest
    Ash Cinder Bomb
  • 9. Volcanic Gases
    • What looks like smoke coming from a volcano is actually a mixture of ash and gases.
      • The main gases in magma are water vapor and carbon dioxide
  • 10. Pyroclastic Flow
    • Volcanic gases can mix with rock fragments and stay near the ground.
    • Pyroclastic flow- a dense cloud of superhot gases and rock fragments.
      • Can reach temperatures of 800 degrees C (1500 degrees F)
      • Can reach speeds of 160 km/hr (100 mi/hr)
      • Pyroclastic flows are the most dangerous type of volcanic eruption.
  • 11. Most volcanoes form along plate boundaries
    • Most of Earth’s volcanic activity takes place under water- along plate boundaries
    • Volcanoes can also occur along hotspots away from plate boundaries- this is less common
  • 12. Types of Volcanoes
    • Shield Volcano – shaped like a broad, flat dome.
    • Built up by man eruptions of lava that is relatively low in silica.
  • 13. Types of Volcanoes
    • Cinder Cone- a steep, cone-shaped hill formed by the eruption of cinders and other rock fragments that pile up around a single crater.
    • Form as gas-rich magma erupts- often on the side of another volcano
    • Ten to hundreds of meters tall
  • 14. Types of Volcanoes
    • Composite Volcano - a cone shaped volcano that is built up of layers of lava and layers of rocks fragments.
    • Steep at the top flattens out at the bottom
    • Tends to have very violent eruptions
  • 15. Caldera
    • Caldera- a huge crater formed by the collapse of a volcano when magma rapidly erupts from underneath it.
  • 16. Active Volcano
    • A volcano that currently vents lava or gases etc, or has the capability of doing so
  • 17. Dormant Volcano
    • A volcano that has not erupted for a considerable length of time, but is still capable of erupting
  • 18. Warning Signs of Volcanic Activity
    • Temperature of rocks in the volcanic cone increases
    • The cone may change shape- swell or bulge just before eruption
    • Small earthquakes and tremors in the area around the volcano
    • Emission or increase of gas from the volcano
    • Often animals may act strangely before the eruption
  • 19. Scientist Monitor Volcanoes
    • Scientist cannot prevent volcanoes from erupting
    • The signs of an eruption can allow people to leave an area so the loss of human life can be minimized
  • 20.