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  1. 1. Chapter 7 VOLCANOES Sect. 1 & 2
  2. 2. Volcanism <ul><li>Mov’t of magma toward or onto the Earth’s surface magma rises cuz its less dense pushing its way to the surface </li></ul><ul><li>Magma on earth’s surface = Lava </li></ul><ul><li>Vent = opening in earth’s surface where magma flows through </li></ul><ul><li>Volcano = structure formed from vent & material builds around it </li></ul>
  3. 3. Major Volcanic zones <ul><li>On divergent & convergent boundaries </li></ul>1. Subduction Zones 2. Mid-Ocean Ridges 3. Hot Spots
  4. 4. Subduction Zones <ul><li>A subducted plate is subjected to heat & friction & is forced downward causing it to remelt & become magma </li></ul><ul><li>This magma will be forced to surface and forming volcanic mountains along continental plate </li></ul>
  5. 5. Subduction Zones <ul><li>Ring of Fire is a result of plates being subducted </li></ul><ul><li>There can also be collision of 2 oceanic plates forming Volcanic Arcs ( ex. Japan ) </li></ul>
  6. 6. Subduction Zones <ul><li>Ring of Fire is a result of plates being subducted </li></ul><ul><li>There can also be collision of 2 oceanic plates forming Island Arcs or volcanic islands ( ex. Japan ) </li></ul>
  7. 7. Mid-Ocean Ridges <ul><li>Divergent boundary </li></ul><ul><li>Magma rises up through rift </li></ul><ul><li>Emerging lava forms new ocean floor </li></ul><ul><li>Iceland is exposed part of ridge & is covered with fissures (cracks) </li></ul>
  8. 8. Hot Spots <ul><li>Magma comes to the surface from within a plate </li></ul><ul><li>Hot spot stays put but plate is in constant motion forming volcanic islands </li></ul>Hawaiian Islands Galapagos Islands
  9. 9. Volcanic Eruptions Windows to Earth’s Interior Ability to see firsthand materials from mantle
  10. 10. 3 General Types of Lava <ul><li>1. Mafic ( basaltic ) low silica content and low in water vapor & CO 2 dark color </li></ul><ul><li>2. Felsic ( granitic ) high silica & high in water vapor & CO 2 </li></ul><ul><li>light in color </li></ul><ul><li>3. Faults between mafic & felsic </li></ul><ul><li>range in composition </li></ul>
  11. 11. Kinds of Eruptions <ul><li>Type of lava (mafic/felsic) determine how explosive eruption will be demo </li></ul><ul><li>Oceanic Volcanoes: produce mafic lava very thin flow easily low gas erupt quietly </li></ul>
  12. 12. Kinds of Eruptions <ul><li>Felsic lava (continental volcanoes) thick lava large amt gases w/lava boil out of vent explosively solid particles fly out w/ magma </li></ul>
  13. 13. Volcanic Rock Fragments <ul><li>Pyroclastics : large fragments blown from the cone of felsic volcanoes. </li></ul>< 2 mm = volcanic ash < .25 mm = volcanic dust < 64 mm = lapilli (lil’ stones)
  14. 14. Three types of Volcanoes <ul><li>Shield Volcano covers wide area quiet eruptions slow build up around vent </li></ul>
  15. 15. Three types of Volcanoes <ul><li>Cinder cone made up of solid fragments Steep slopes rarely high very explosive </li></ul>
  16. 16. Three types of Volcanoes <ul><li>Composite Cone </li></ul>
  17. 17. Three types of Volcanoes <ul><li>Composite Cone formed by alternating explosive & quiet eruptions develop high volcanic mountains </li></ul>
  18. 19. Crater vs. Caldera <ul><li>Crater = funnel shaped pit at top of vent; formed when material is blown from vent during explosions </li></ul><ul><li>Caldera = large basin shaped depressions formed either by explosions or cones collapsing </li></ul>
  19. 20. Predicting Volcanoes <ul><li>seismographs </li></ul><ul><li>study past history of volcanoes </li></ul><ul><li>bulging of volcanic slopes </li></ul><ul><li>changes in gases given off </li></ul>
  20. 21. Extraterrestrial Volcanism Many planets & moons in the solar system were and are volcanically active
  21. 22. Extraterrestrial Volcanism The Moon Covered by Basaltic flows; no longer active; however, no evidence of plate tectonic activity
  22. 23. Extraterrestrial Volcanism Mars Numrous volcanoes & features; biggest one is shield volcano called Olympus Mons
  23. 24. Extraterrestrial Volcanism IO Moon on Jupiter; shows 9 active volcanoes erupting on Io