Volcanoes chapter 29


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Volcanoes chapter 29

  1. 1. Volcanoes Chapter 29.1
  2. 2. Unit Ten: Earth Science Chapter 29 Formation of Rocks 29.1 Volcanoes 29.2 The Surface of Earth 29.3 Rocks and Minerals
  3. 3. 29.1 Volcanoes The eruption of Mount St. Helens in 1980 reduced the height of this mountain from 2,932 meters (9,677 feet) to 2,535 meters (8,364 feet). Early in the morning of May 18, 1980, an earthquake triggered a landslide that caused the bulge to eject magma, water, and gases.
  4. 4. Mount St. Helens
  5. 5. 29.1 Volcanoes *Solid rock melts and becomes magma under certain conditions that lower the melting point of the material. *At subduction zones, water is the key for solid rock to melt and become magma.
  6. 6. 29.1 Volcanoes *Most volcanic activity is found at the edges of tectonic plates, namely at divergent and convergent plate boundaries, but does not occur at transform plate boundaries.
  7. 7. Shield Volcanoes: *Low viscosity, fast- flowing lava is associated with shield volcanoes. Because this lava easily flows down hill, shield volcanoes are gently sloped and flattened.
  8. 8. Composite Volcanoes *High viscosity lava is associated with stratovolcanoes (also called composite volcanoes). These volcanoes range in height from 500 to 10,000 meters high.
  9. 9. Cinder Cone Volcanoes *Cinder cone volcanoes are steep stacks of loose pyroclasts (clumps and particles of lava). Cinder cones are rarely higher than 300 meters.
  10. 10. Lava Facts: *Lava Explosive eruptions occur when the lava has a lot of water and dissolved gases. Gentle eruptions are associated with fast-flowing lava from oceanic crust. viscosity also determines how explosive an eruption will be.
  11. 11. Where volcanoes form Volcanoes also form when an oceanic plate slides under another oceanic plate.
  12. 12. Hydrothermal Vents *Hydrothermal vents are deep sea, chimney-like structures that occur along midocean ridges.
  13. 13. Gemstones Some gemstones are also associated with volcanic activity. For example, diamonds form at high temperatures deep underground when carbon crystallizes inside rocks called kimberlites.
  14. 14. Geothermal Energy *Geothermal energy is the useful product of volcanic activity. When steam from magma collects below ground, it can be tapped just like water in a well. *The pressurized steam can be used to generate electricity.
  15. 15. 29.1 Volcanoes *Volcanic activity results in the formation of two kinds of igneous rocks:  extrusive  intrusive A batholith is a large underground rock that formed when a mass of magma cooled underground.
  16. 16. Key Questions:1. Why do some volcanoes erupt explosively?2. Which volcanoes have a slow flow of lava down the slopes?3. Where do volcanoes occur?4. What ocean does the Ring of Fire surround?