What Controls Volcanic Eruptions? Ch 12.2
Some eruptions are quiet…
Some eruptions are EXPLOSIVE! Mt. Pinatubo Mont serrat Mt. St. Helens
What Controls Volcanic Eruptions? <ul><li>How much water vapor (a gas) and other gases are trapped in the erupting magma <...
<ul><li>water vapor and carbon dioxide are dissolved in  magma </li></ul><ul><ul><li>When magma rises to surface, gases es...
Water may be added to magma when ocean crust rock is melted at convergent plate boundaries
 
Composition of magma <ul><li>Silica-rich magma is called  granitic magma </li></ul><ul><li>Results in explosive eruptions ...
Basaltic magma may result in different lava types: <ul><li>Pahoehoe </li></ul><ul><li>AA </li></ul><ul><li>Pillow </li></ul>
<ul><li>Pahoehoe lava:   </li></ul><ul><li>Hot, thin, fast flowing  </li></ul><ul><li>harden with a relatively smooth surf...
<ul><li>Pahoehoe lava </li></ul>
<ul><li>Aa lava:  </li></ul><ul><li>Cooler,  thicker , slow moving </li></ul><ul><li>Hardens with a rough, jagged, sharp e...
<ul><ul><li>Pillow Lava:  </li></ul></ul><ul><ul><li>Lava cools underwater </li></ul></ul><ul><ul><li>resembles stuffed pi...
Name That Lava Type!
Name That Lava Type!
Name That Lava Type!
Name That Lava Type!
Composition of magma <ul><li>Andesitic magma – more silica than basaltic magma, but less than granitic magma </li></ul><ul...
 
Krakatau  1883 Sound heard 3,000 mi away!  13,000 x more powerful than nuclear blast at Hiroshima in WWII
Anak Krakatau  (Child of Krakatau)
Forms of Volcanoes <ul><li>Depends on: </li></ul><ul><ul><li>Type of magma it was formed from </li></ul></ul><ul><ul><li>T...
1.  Shield volcanoes Mauna Kea, Hawaii
Shield volcanoes Mauna Loa, Hawaii
Shield volcanoes <ul><li>Result of quiet eruptions of basaltic lava flows (no ash) </li></ul><ul><li>May form volcanic con...
Shield volcano
Fissure eruption
Fissure eruptions <ul><li>Common at divergent plate boundaries, mid-ocean ridges </li></ul>
Columbia Plateau
2.  Cinder Cone Volcanoes
Cinder Cone Volcanoes
Cinder Cone Volcanoes
Cinder cone example:  Paricut í n, Mexico 1943
Cinder Cones <ul><li>Small base, steep-sided, loosely consolidated </li></ul><ul><li>Up to 1000 feet tall </li></ul><ul><l...
Tephra <ul><li>Names are based on size: </li></ul><ul><li>Ash </li></ul><ul><li>Cinders  </li></ul><ul><li>Bombs </li></ul...
Ash
Cinders
Bombs
Blocks
Cinder Cone Volcanoes
3.  Composite Volcanoes <ul><li>Steep slope (30 o )  </li></ul><ul><li>Made of multiple  lava  and  ash  flows </li></ul><...
Composite Volcanoes
Composite Volcanoes
Composite Volcanoes
<ul><ul><li>Composite Volcanoes:   </li></ul></ul>Mt. Rainier Mt. Fuji
Composite Volcanoes:   Mt. Kilimanjaro Pinatubo
Composite Volcano examples: Soufri è re Hills, Montserrat
Composite Volcano examples: Mt Rainier, Washington
What city is near Mt. Rainer?
Consider: <ul><ul><li>100,000 people live on the solidified mudflows of previous eruptions </li></ul></ul><ul><ul><li>The ...
<ul><li>Lahar (mudflow):  </li></ul><ul><li>mixture of  ash, eroded land , and water flowing down river valleys </li></ul>
<ul><ul><li>Lahar flows average every  500 years  and have gone as far as the Puget Sound lowlands (1 in 7 chance of it ha...
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Volcanoes 12 2 Notes 08 09

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Volcanoes 12 2 Notes 08 09

  1. 1. What Controls Volcanic Eruptions? Ch 12.2
  2. 2. Some eruptions are quiet…
  3. 3. Some eruptions are EXPLOSIVE! Mt. Pinatubo Mont serrat Mt. St. Helens
  4. 4. What Controls Volcanic Eruptions? <ul><li>How much water vapor (a gas) and other gases are trapped in the erupting magma </li></ul><ul><li>How much silica is contained in the magma </li></ul>
  5. 5. <ul><li>water vapor and carbon dioxide are dissolved in magma </li></ul><ul><ul><li>When magma rises to surface, gases escape because they are under less pressure </li></ul></ul><ul><ul><li>Some magma is thin and fluid- this lets gases escape easily- resulting in quiet eruption </li></ul></ul><ul><ul><li>Other magma is thick and stiff- when gases erupt it results in explosive eruption </li></ul></ul>
  6. 6. Water may be added to magma when ocean crust rock is melted at convergent plate boundaries
  7. 8. Composition of magma <ul><li>Silica-rich magma is called granitic magma </li></ul><ul><li>Results in explosive eruptions </li></ul><ul><li>Ex. Soufriere Hills in Montserrat </li></ul><ul><li>Characteristic of convergent plates </li></ul><ul><li>Silica-poor magma is called basaltic magma </li></ul><ul><li>Results in quiet eruptions </li></ul><ul><li>Ex. Kilauea in Hawaii </li></ul>
  8. 9. Basaltic magma may result in different lava types: <ul><li>Pahoehoe </li></ul><ul><li>AA </li></ul><ul><li>Pillow </li></ul>
  9. 10. <ul><li>Pahoehoe lava: </li></ul><ul><li>Hot, thin, fast flowing </li></ul><ul><li>harden with a relatively smooth surface </li></ul><ul><li>Often has a ropy or wrinkled appearance </li></ul>
  10. 11. <ul><li>Pahoehoe lava </li></ul>
  11. 12. <ul><li>Aa lava: </li></ul><ul><li>Cooler, thicker , slow moving </li></ul><ul><li>Hardens with a rough, jagged, sharp edge surface </li></ul>
  12. 13. <ul><ul><li>Pillow Lava: </li></ul></ul><ul><ul><li>Lava cools underwater </li></ul></ul><ul><ul><li>resembles stuffed pillows </li></ul></ul>
  13. 14. Name That Lava Type!
  14. 15. Name That Lava Type!
  15. 16. Name That Lava Type!
  16. 17. Name That Lava Type!
  17. 18. Composition of magma <ul><li>Andesitic magma – more silica than basaltic magma, but less than granitic magma </li></ul><ul><ul><li>Common at convergent boundaries </li></ul></ul><ul><ul><li>Named after the Andes Mountains in South America </li></ul></ul><ul><ul><li>Also violent eruptions </li></ul></ul><ul><ul><li>Ex. Krakatau- one of the most violent eruptions in history </li></ul></ul>
  18. 20. Krakatau 1883 Sound heard 3,000 mi away! 13,000 x more powerful than nuclear blast at Hiroshima in WWII
  19. 21. Anak Krakatau (Child of Krakatau)
  20. 22. Forms of Volcanoes <ul><li>Depends on: </li></ul><ul><ul><li>Type of magma it was formed from </li></ul></ul><ul><ul><li>Type of eruption- quiet or explosive </li></ul></ul><ul><li>3 basic types of volcanoes </li></ul><ul><ul><li>Shield </li></ul></ul><ul><ul><li>Cinder cone </li></ul></ul><ul><ul><li>Composite </li></ul></ul>
  21. 23. 1. Shield volcanoes Mauna Kea, Hawaii
  22. 24. Shield volcanoes Mauna Loa, Hawaii
  23. 25. Shield volcanoes <ul><li>Result of quiet eruptions of basaltic lava flows (no ash) </li></ul><ul><li>May form volcanic cones or fissures- long cracks that result if flood basalts (Ragged Mtn, Lamentation Mtn) </li></ul><ul><li>Ex. Hawaiian Islands and the Columbia Plateau of Northwest US </li></ul>
  24. 26. Shield volcano
  25. 27. Fissure eruption
  26. 28. Fissure eruptions <ul><li>Common at divergent plate boundaries, mid-ocean ridges </li></ul>
  27. 29. Columbia Plateau
  28. 30. 2. Cinder Cone Volcanoes
  29. 31. Cinder Cone Volcanoes
  30. 32. Cinder Cone Volcanoes
  31. 33. Cinder cone example: Paricut í n, Mexico 1943
  32. 34. Cinder Cones <ul><li>Small base, steep-sided, loosely consolidated </li></ul><ul><li>Up to 1000 feet tall </li></ul><ul><li>Life span of a few years </li></ul><ul><li>Commonly built from solidified rock thrown through the air called tephra </li></ul><ul><li>Has violent eruptions, dangerous when close </li></ul>
  33. 35. Tephra <ul><li>Names are based on size: </li></ul><ul><li>Ash </li></ul><ul><li>Cinders </li></ul><ul><li>Bombs </li></ul><ul><li>Blocks </li></ul>
  34. 36. Ash
  35. 37. Cinders
  36. 38. Bombs
  37. 39. Blocks
  38. 40. Cinder Cone Volcanoes
  39. 41. 3. Composite Volcanoes <ul><li>Steep slope (30 o ) </li></ul><ul><li>Made of multiple lava and ash flows </li></ul><ul><li>Explosive </li></ul>
  40. 42. Composite Volcanoes
  41. 43. Composite Volcanoes
  42. 44. Composite Volcanoes
  43. 45. <ul><ul><li>Composite Volcanoes: </li></ul></ul>Mt. Rainier Mt. Fuji
  44. 46. Composite Volcanoes: Mt. Kilimanjaro Pinatubo
  45. 47. Composite Volcano examples: Soufri è re Hills, Montserrat
  46. 48. Composite Volcano examples: Mt Rainier, Washington
  47. 49. What city is near Mt. Rainer?
  48. 50. Consider: <ul><ul><li>100,000 people live on the solidified mudflows of previous eruptions </li></ul></ul><ul><ul><li>The danger is mostly from lahars traveling down river valleys at a speed of 25mph and destroying everything in its path </li></ul></ul>
  49. 51. <ul><li>Lahar (mudflow): </li></ul><ul><li>mixture of ash, eroded land , and water flowing down river valleys </li></ul>
  50. 52. <ul><ul><li>Lahar flows average every 500 years and have gone as far as the Puget Sound lowlands (1 in 7 chance of it happening during your lifetime) </li></ul></ul><ul><ul><li>Mount Rainier has erupted 4 times in the last 4000 years with the last eruption 200 years ago </li></ul></ul>

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