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Volcanic Activity

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  1. Volcanic Activity EQ: What occurs when a volcano erupts? How do the different type of eruptions differ?

  2. How Magma Reaches Earth’s Surface • Magma rises because it is less dense that the surrounding solid material

  3. What happens when a volcano erupts? • As the less dense magma rises, the pressure decreases • The dissolved gas separates out and bubbles form • A volcanic erupts when an opening develops in weak rock on the surface • During a volcanic eruption, the gases dissolved in magma rush out, carrying the magma with them • Once magma reaches the surface and becomes lava, the gases bubble out

  4. Inside a Volcano

  5. Magma Chamber • The pocket beneath a volcano where magma collects

  6. Pipe • A long tube through which magma moves from the magma chamber to Earth’s surface

  7. Vent • The opening through which molten rock and gas leave a volcano

  8. Where are vents located? • Usually there is one central vent at the top of the volcano • Often times there are additional vents that open on the volcanoes sides

  9. Lava Flow • The area covered by lava as it pours out of a volcano’s vent

  10. Crater • A bowl-shaped area that forms around a volcano’s central opening • Lava collects there

  11. How does magma rise through the lithosphere? • Liquid magma in the asthenosphere is less dense than the rock in the lithosphere above it, so it flows upward through cracks in the rock • The magma is stored in the magma chamber • It continues upward (through the pipe) until it reaches the surface (exiting through a vent) or it is trapped beneath layers of rock.

  12. Silica • A material that is found in magma,formed from the elements oxygen and silicon • The more silica the magma has the thicker it is

  13. Three factors contribute to how forceful a volcanic eruption is . • Amount of gas present • How thick or thin the magma is (Temperature) • Thinner (hotter) is more fluid • The silica content • If the silica content is high, magma is thick • This causes the pressure to build

  14. Types of Volcanic Eruptions

  15. Quiet Eruptions • Classified as a quiet eruption if its magma flows easily • The gas in this magma bubbles out gently • Quiet eruptions produce two types of lava: • Pahoehoe – (pah HOH ee hoh ee) • aa – (Ah ah)

  16. Pahoehoe • A hot, fast-moving type of lava that hardens to form smooth, ropelike coils. Cools slowly resulting in a smooth texture

  17. Aa • A cooler, slow-moving type of lava that hardens to form rough chunks; cooler than Pahoehoe. Cools more quickly

  18. What accounts for the differences between these two types of lava? • The temperature of the lava • The speed at which the lava flows

  19. Explosive Eruptions • Magma that is thick and sticky causes a volcano to erupt explosively • Magma can not flow freely causing pressure (gas) to build up until it explodes

  20. Pyroclastic flow • The expulsion of ash, cinders, and bombs from a violent volcanic explosion

  21. How do the two types of volcanic eruptions differ? • Quiet eruptions occur when the lava flows more easily because gas dissolved in the magma bubbles • When the lava is thick and sticky the gas continues to store increasing pressure • When the pressure becomes so great an explosion takes place when the gas pushes the magma out with incredible force

  22. Three Stages of Volcanoes • Active • A volcano that is erupting or has shown signs that it may erupt in the near future • Dormant • A volcano that is not currently active, but may become active in the future • Extinct • A volcano that is unlikely to erupt again

  23. Hot Spring • A pool formed by groundwater that has risen to the surface after being heated by a nearby body of magma

  24. Geyser • A fountain of water and steam that builds up pressure underground and erupts at regular intervals

  25. Geothermal Energy • Energy from water and steam that has been heated by magma • Geothermal energy is produced by drilling a well into the ground where thermal activity is occuring. • Once a well has been identified and a well head attached, the steam is separated from the water, the water is diverted through a turbine engine which turns a generator. • Usually the water is injected back into the ground to resupply the geothermal source.

  26. Monitoring the activity of a volcano • Measure tilt caused by magma movement underground using tiltmeters & laser-ranging devices • Monitor temperature underground • Monitor small earthquakes that occur in the area around a volcano

  27. Hazards of Volcanoes • Fire • Bury entire towns • Damage crops • Landslides • Avalanches of mud • Damage car and jet engines