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Volcanoes!

Learn about the causes of volcanic eruptions, the formation of different types of volcanoes, and the factors that determine eruption types. Explore how magma forms and rises to the surface, and discover the different materials produced during volcanic eruptions. Discover the tools scientists use to predict volcanic eruptions and study the formation of calderas.

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Volcanoes!

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  1. Volcanoes! Chapter 13 Volcanoes 101 Videoclip

  2. Section 1 • Many volcanic eruptions are caused by moving plates- often on or around plate boundaries • Most volcanoes are found near the Ring of Fire along the Pacific Plate (see map) • Volcanoes are found: • Subduction zones • Mid Ocean Ridges • Hot spots (visual concepts-online book)

  3. Subduction Zones • Site of many volcanoes and trench formation • Plates slide underneath another plate

  4. Ring of Fire Reminds me of a song……..

  5. Mid Ocean Ridges • Divergent boundaries form new crust as lava cools • Most eruptions are not noticed because they are under water

  6. Hot Spots • Not on plate boundaries • Columns of hot material from the mantle-plumes • When the lithosphere drifts, hot spot moves to a different location, creating a new volcano and new continental crust ex) Hawaiian Islands

  7. Hot Spots

  8. Formation of Magma • Liquid rock • Rock has a melting point at which it becomes liquid • Magma can form under 3 conditions: • Temperature exceeds melting point of minerals in rock • Pressure from surrounding rock is removed • Fluids such as water are added and lower the melting point

  9. Magma • Can be described as • Mafic-high in iron and magnesium –dark in color-forms oceanic crust • Felsic –high in silica-light colored-forms continental crust • See the visual concept on magma formation Q: Why does magma rise to the surface? Magma is less dense than surrounding rock

  10. Volcanism • Any activity in which magma rises to the surface • Magma is less dense than rock • Volume of magma increases-magma melts rock as it rises to the surface • Volcano-vent through which magma and gases travel to the surface • Lava-magma on the surface Brain POP: Volcanoes

  11. Intrusive Activity • When magma does not reach the Earth’s surface, the magma may cool and solidify inside the Earth • This formation is called a pluton Devil’s Tower, Wyoming

  12. Eruption Types Quiet Explosive Viscosity: resistance to flow

  13. Quiet Eruptions Lava has low viscosity-gases can escape easily-usually mafic lava

  14. Lava Flows aa Pahoehoe aa Pahoehoe Blocky Pillow

  15. Explosive Eruptions Lava has high viscosity-high amount of trapped gases-usually felsic lava

  16. Pyroclastic Materials • Rocks that form from lava during an eruption • Classified according to size • Volcanic dust-less than .25 mm • Volcanicash- .26 mm to 2 mm • Lapilli- 2 mm to 64 mm • Volcanic Bombs-large clots of lava-rounded shape • Volcanic Blocks-the largest rock particles-solid rock blasted from the vent

  17. Types of Volcanoes Shield Cinder Cones Composite or Stratovolcano

  18. Shield Volcanoes Broad at the base with gently sloping sides Quiet eruptions, mafic lava, found at hot spots and diverging boundaries Ex) Hawaiian volcanoes

  19. Cinder Cones Usually the smallest in size, steep slopes, small explosive eruptions, felsic lava, converging boundaries

  20. Composite or Stratovolcanoes Large in size, quiet and explosive eruptions, steep slopes, both mafic and felsic lava, convergent boundaries

  21. Mount St. Helens Composite Volcano in Washington

  22. Eruption May 18, 1980

  23. Eruption May 18, 1980 USGS Video What information do scientists use to predict volcanic eruptions? Are eruptions a single event or a group of multiple eruptions? Before and After Photos

  24. Calderas-How do they form? Crater Lake Oregon Caldera Formation Demo-USGS

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