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Normally the geotherm does not cross the solidus, so there is no melting.

Rock melts when the temperature within the earth ( geotherm ) exceeds the melting point ( solidus ) of rock. This happens for different reasons at (1) subduction zone volcanoes, (2) mid-ocean ridge volcanoes, and (3) hotspot volcanoes.

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Normally the geotherm does not cross the solidus, so there is no melting.

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  1. Rock melts when the temperature within the earth (geotherm) exceeds the melting point (solidus) of rock. This happens for different reasons at (1) subduction zone volcanoes, (2) mid-ocean ridge volcanoes, and (3) hotspot volcanoes.

  2. Normally the geotherm does not cross the solidus, so there is no melting. (THE MANTLE IS SOLID!!!!) BUT, it is very close at about 100-250 km in depth ( Asthenosphere).

  3. What are the 4 main forms of volcanoes? 1. Seafloor Subduction

  4. Subduction Zones: “wet” melting

  5. Mt. Fujiyama

  6. Cotopaxi Volcano, Equador

  7. Cotopaxi, by Frederic Church, 1862

  8. Stratovolcano (Composite Cone)

  9. Cerro Negro, Nicaragua

  10. Cerro Negro, Nicaragua

  11. Paricutin, Mexico (1946)

  12. Mayon, Philippines (1984)

  13. Pacaya, Guatemala

  14. Pacaya, Guatemala (Agua volcano in background)

  15. Pacaya, Guatemala (2004)

  16. Pyroclastic flow sweeps down the side of Mayon Volcano, Philippines, 1984.

  17. Mayon, Philippines (1984)

  18. Mayon, Philippines (1984)

  19. Mayon, Philippines (2000)

  20. Mt. Pinatubo, Philippines, 1991.

  21. Pinatubo, Philippines (1991)

  22. Pinatubo, Philippines (1991)

  23. Pinatubo, Philippines (1991)

  24. A small lahar triggered by rainfall in Guatemala, 1989.

  25. Pinatubo, Philippines (1991)

  26. Pinatubo, Philippines (1991)

  27. Mt. Pinatubo: So much ash into the atmosphere that Earth’s temperature dropped, and sunsets were redder.

  28. What are the 4 main forms of volcanoes? 2. Mid-Ocean Seafloor Spreading

  29. Ridges: “pressure release” melting

  30. Figure 4-15b

  31. Ocean Crust Layers

  32. What are the 4 main forms of volcanoes? 3. Continental Rifting

  33. Continental Rifting leaves a complex structure beneath passive margins like the east coast of North America

  34. What are the 4 main forms of volcanoes? 4. Hotspot Mantle Plumes

  35. Hawaii rises more than 5 miles above the seafloor.

  36. Hawaii

  37. Kilauea, Hawaii Mauna Loa, Hawaii

  38. Figure 4-7b

  39. Kilauea, Hawaii

  40. Figure 3-1

  41. Pahoehoe lava, Hawaii

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