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Volcanoes

Volcanoes Processes that Form Magma in the Crust and Upper Mantle Increase in temperature Pressure-Release Melting: decrease in confining pressure lowers the melting point of rock Addition of water lowers the melting point of rock Fig. 8-2, p.171 Environments of Magma Formation

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Volcanoes

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  1. Volcanoes

  2. Processes that Form Magma in the Crust and Upper Mantle • Increase in temperature • Pressure-Release Melting: decrease in confining pressure lowers the melting point of rock • Addition of water lowers the melting point of rock

  3. Fig. 8-2, p.171

  4. Environments of Magma Formation • Spreading centers associated with divergent boundaries • Subduction zones associated with convergent boundaries • Mantle plumes

  5. Pressure-release melting at spreading center

  6. Fig. 8-7, p.173

  7. Fig. 8-6, p.173

  8. Figure 4.27

  9. Partial Melting and Magma Formation • Formation of Basaltic magmas • Most originate from partial melting of ultramafic rock in the mantle • Basaltic magmas form at mid-ocean ridges by decompression melting or at subduction zones • Formation of Granitic magmas • Basaltic magma pools beneath granitic continental rock and melts it, forming granitic magma • Granitic magma often does not reach the surface, but instead forms intrusive rocks at depth.

  10. How Magma Rises

  11. Formation of Plutons from Granitic Magma • Formation of Granitic magmas • Basaltic magma pools beneath granitic continental rock and melts it, forming granitic magma • Granitic magma often does not reach the surface, but instead forms intrusive rocks at depth. • Pluton – a large mass of intrusive rock • Most plutons are granitic in composition • Granitic magma forms at base of continental crust and rise up because it is less dense

  12. Forming Igneous Features and Landforms

  13. Fig. 8-15, p.179

  14. Fig. 8-16, p.180

  15. Figure 4.24

  16. Figure 4.26

  17. Volcanoes • Types of Volcanoes • Shield volcano • Broad, slightly domed-shaped • Composed primarily of basaltic lava • Generally cover large areas • Produced by mild eruptions of large volumes of lava • Mauna Loa on Hawaii is a good example

  18. Volcanoes • Types of Volcanoes continued • Cinder cone • Built from ejected lava (mainly cinder-sized) fragments • Steep slope angle • Rather small size • Frequently occur in groups

  19. Sunset Crater – a cinder cone near Flagstaff, Arizona Copyright © 2006 Pearson Prentice Hall, Inc.

  20. Volcanoes • Types of volcanoes continued • Composite cone (Stratovolcano) • Most are located adjacent to the Pacific Ocean (e.g., Fujiyama, Mt. St. Helens) • Large, classic-shaped volcano (1000’s of ft. high & several miles wide at base) • Composed of interbedded lava flows and layers of pyroclastic debris

  21. Figure 4.1a

  22. A composite volcano Figure 4.7

  23. Figure 4.20

  24. Plate Tectonics and Magma Generation

  25. Tectonic Settings and Volcanic Activity

  26. Formation of Crater Lake

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