Volcanoes

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Class notes on volcanoes

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Volcanoes

  1. 1. Volcanoes
  2. 2. <ul><li>Volcano : </li></ul><ul><li>an opening in the earth’s surface through which lava, hot gases, and rock fragments erupt </li></ul>Introduction to volcanoes
  3. 3. <ul><ul><li>Magma 50-100 miles below the earth’s surface slowly begins to rise to the surface </li></ul></ul><ul><ul><li>As the magma rises it melts gaps in the surrounding rock </li></ul></ul><ul><ul><li>As more magma rises a large reservoir forms as close as 2 miles below the surface (magma chamber) </li></ul></ul>Origin of Volcanoes
  4. 4. <ul><ul><li>Pressure from the surrounding rock causes the magma to blast or melt a conduit (channel) to the surface where magma erupts onto the surface through a vent (opening) </li></ul></ul>Origin of Volcanoes
  5. 5. <ul><ul><li>The magma, now called lava, builds up at the vent forming a volcano </li></ul></ul>Origin of Volcanoes
  6. 6. <ul><ul><li>6. Often the volcano sides will be higher than the vent forming a depression called a crater </li></ul></ul>Origin of Volcanoes
  7. 7. <ul><li>Crater : </li></ul>
  8. 8. <ul><li>Caldera: </li></ul><ul><li>an unusually large crater or the remains when the cone collapses into its own magma chamber </li></ul>
  9. 9. Anatomy of a Volcano <ul><li>Cone : </li></ul><ul><li>the above ground structure built from lava and/or tephra </li></ul>
  10. 10. <ul><li>Conduit : </li></ul><ul><li>the path that magma takes from the magma chamber to the vent </li></ul>
  11. 11. <ul><li>Magma Chamber : </li></ul><ul><li>the reservoir located under the volcano where magma collects and becomes the supply of magma/lava to build the volcano </li></ul>
  12. 12. <ul><li>Parasitic Cone: </li></ul><ul><li>a smaller secondary volcano built on the side of or near the main volcano, but sharing the same conduit to the magma chamber </li></ul>
  13. 13. <ul><li>Fumarole: </li></ul><ul><li>a secondary vent that emits only gases </li></ul>
  14. 14. <ul><li>Fissure : </li></ul><ul><li>a long fissure (crack) from which lava flows </li></ul>
  15. 15. <ul><li>Vent : opening of the volcano, through which lava, ash and gases flow </li></ul>
  16. 16. Take a minute to label the parts on the diagram (not all parts are shown)
  17. 17. Magma chamber conduit mantle Parasitic Cone Ash Cloud/Gases Vent Lava Flow Crater
  18. 18. <ul><li>Lava— There is 3 kinds: </li></ul>
  19. 19. <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>
  20. 20. <ul><li>Pahoehoe lava: </li></ul>
  21. 21. <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>
  22. 22. <ul><ul><li>Pillow Lava: </li></ul></ul><ul><ul><li>Lava suddenly cooled by water </li></ul></ul><ul><ul><li>shows sack-like segments (stuffed pillows) </li></ul></ul>
  23. 23. Can you identify the kinds of lava from the pictures? Circle your choice.
  24. 24. #1 AA
  25. 25. #2 Pahoehoe
  26. 26. #3 Pillow
  27. 27. #4 AA & PahoeHoe
  28. 28. <ul><li>Tephra (pyroclastic, rock fragments) </li></ul><ul><li>Volcanic Dust : Smallest particles and carried by atmosphere circulation </li></ul>
  29. 29. <ul><ul><li>Volcanic Ash: </li></ul></ul><ul><ul><li>0.25-0.5 cm diameter </li></ul></ul><ul><ul><li>Generally settles out within miles of the cone but can be carried greater distances by stronger winds. </li></ul></ul><ul><ul><li>Forms a mudflow when mixed with water </li></ul></ul>
  30. 30. <ul><ul><li>Bomb : </li></ul></ul><ul><ul><li>Smaller bombs (gravel, pea size) are called cinders . </li></ul></ul><ul><ul><li>Walnut size bombs are called lapilli . </li></ul></ul><ul><ul><li>Larger fragments up to 4+ feet in diameter are called bombs. </li></ul></ul>
  31. 31. <ul><li>Lahar (mudflow): </li></ul><ul><li>mixture of ash, eroded land , and water flowing down river valleys </li></ul>
  32. 32. <ul><li>Lahar (mudflow): </li></ul>
  33. 33. <ul><li>Gases : </li></ul><ul><li>water vapor, carbon dioxide , nitrogen, sulfur dioxide , hydrogen sulfide, chlorine </li></ul>
  34. 34. <ul><ul><li>Divergent Boundaries: </li></ul></ul><ul><ul><li>As the plate move long cracks (rifts) form and lava builds up forming </li></ul></ul><ul><ul><li>volcanoes. </li></ul></ul>Locations of Volcanoes
  35. 35. <ul><ul><li>If the boundary is on the ocean floor, volcanoes can grow tall enough to break the surface of the ocean and become islands (Iceland) </li></ul></ul>
  36. 36. <ul><li>Convergent Boundaries: </li></ul><ul><li>Places where plates are moving toward each other forming a subduction zone . </li></ul><ul><li>One plate melts under the other and the magma moves upward to form volcanoes. </li></ul>
  37. 37. <ul><li>Example: Pacific Ring of Fire </li></ul>
  38. 38. <ul><li>Example: Cascade Volcanoes </li></ul>
  39. 39. <ul><li>Magma that may originate in the mantle or outer core will move upward, breaking the surface and forming a volcano, they are independent of plate boundaries and a chain of volcanoes may form as the plate moves across a hot spot. </li></ul>Hot Spots
  40. 40. <ul><li>(Examples: Hawaiian Islands and Yellowstone National Park) </li></ul>Hot Spots
  41. 41. <ul><ul><li>Two factors determine the type of eruption : </li></ul></ul><ul><ul><li>Amount of water vapor & other gases in the magma </li></ul></ul><ul><ul><li>The chemical composition of the magma </li></ul></ul>Types of Volcanic Eruptions
  42. 42. <ul><ul><li>Trapped gases under high pressure will violently explode when the magma reaches the lower pressure of the surface. </li></ul></ul><ul><ul><li>Has granitic magma is very thick and plugs the vent causing the pressure to build until it blows violently out the vent </li></ul></ul><ul><ul><li>The high water content of the magma produces more water vapor which when mixed in granitic magma produces explosive eruptions </li></ul></ul>Explosive Eruptions
  43. 43. Explosive Eruptions Mt. St. Helens Mont serrat Mt. Pinatubo
  44. 44. <ul><ul><li>Low pressure gas </li></ul></ul><ul><ul><li>Has basaltic magma (is more fluid and will flow instead of explode) </li></ul></ul><ul><ul><li>And has low water content </li></ul></ul>Quiet Eruptions
  45. 45. <ul><ul><li>Cinder Cones : </li></ul></ul><ul><ul><li>Small base , steep-sided, loosely consolidated </li></ul></ul><ul><ul><li>Up to 1000 feet tall </li></ul></ul><ul><ul><li>Life span of a few years </li></ul></ul><ul><ul><li>Commonly built from gravel size lava rock fragments call cinders </li></ul></ul><ul><ul><li>Has violent eruptions, dangerous when close. </li></ul></ul>Types of Volcano Mountains
  46. 46. Cinder Cone Volcanoes
  47. 47. <ul><ul><li>Cinder Cones : </li></ul></ul>Types of Volcano Mountains
  48. 48. <ul><ul><li>High pressure gas bubbles causes thick lava to explode into the air, lava begins to cool as it rises and falls becoming very sticky </li></ul></ul><ul><ul><li>When lava hits the ground it sticks rather than flows </li></ul></ul><ul><ul><li>This builds a steep cone with a small base </li></ul></ul>
  49. 49. Sketch a Cinder Cone Volcano:
  50. 50. Types of Volcano Mountains <ul><li>Shield Volcanoes: </li></ul><ul><li>Large base, gentle slope , lava rock layers </li></ul><ul><li>A few miles wide </li></ul><ul><li>Life span of a million years or more </li></ul><ul><li>The lava is hot, thin, very fluid , often basaltic . </li></ul><ul><li>Example : Hawaiian Islands </li></ul>
  51. 51. Shield volcano on Mars; Taken from space Shield Volcanoes Take a look at these examples: http://www.volcano.si.edu/world/tpgallery.cfm?category=Shield%20Volcanoes The Mauna Loa volcano in Hawaii—the largest volcano on Earth—has the broad expanse characteristic of shield volcanoes. It spreads across half the island of Hawaii.
  52. 52. <ul><li>Shield Volcanoes </li></ul>Mauna Kea
  53. 53. Sketch a sheild Volcano:
  54. 54. <ul><ul><li>Composite (strato) Volcanoes: </li></ul></ul><ul><ul><li>Large mountain volcano often snow capped , a few miles high </li></ul></ul><ul><ul><li>Life span of million years or more </li></ul></ul><ul><ul><li>Have alternating eruptions of tephra (air-borne) and lava . The tephra adds height to the volcano and the lava cements the tephra together and adds to the base . </li></ul></ul><ul><ul><li>Found mostly in subduction zones and have violent eruptions. </li></ul></ul><ul><ul><li>Examples : Mt Rainier, Mt Fuji, Mt Kilimanjaro </li></ul></ul>Types of Volcano Mountains
  55. 55. <ul><ul><li>Composite (strato) Volcanoes: </li></ul></ul>Mt. Rainier Mt. Fuji Mt. Kilimanjaro
  56. 56. Sketch a composite Volcano:
  57. 57. <ul><ul><li>Active (awake): </li></ul></ul><ul><ul><li>Has erupted within recent time and can erupt again at any time . </li></ul></ul><ul><ul><li>Pre-eruption activities : </li></ul></ul><ul><ul><ul><li>Increase in earthquake activity under the cone </li></ul></ul></ul><ul><ul><ul><li>increase in temperature of cone, </li></ul></ul></ul><ul><ul><ul><li>melting of ice/snow in the crater </li></ul></ul></ul><ul><ul><ul><li>swelling of the cone </li></ul></ul></ul><ul><ul><ul><li>steam eruptions </li></ul></ul></ul><ul><ul><ul><li>minor ash eruptions </li></ul></ul></ul>Volcano Activity Levels (Stages)
  58. 58. Mt St. Helens
  59. 59. <ul><li>Dormant (sleeping): </li></ul><ul><li>No eruption within recent times, but there is record of past eruptions </li></ul><ul><li>Can become active and erupt again after a “wake up” period </li></ul><ul><li>Example : Mt. Rainier </li></ul>
  60. 60. <ul><li>Extinct: </li></ul><ul><li>No eruption within recorded history </li></ul><ul><li>Not expected to ever erupt again </li></ul><ul><li>Example: Mount Mazama (Crater Lake) </li></ul>
  61. 61. Crater Lake
  62. 62. <ul><li>Mount Rainier </li></ul><ul><ul><li>The most dangerous volcano in the US </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><ul><ul><li>100,000 people live on the solidified mudflows of previous eruptions </li></ul></ul>
  63. 63. <ul><li>Mount Rainier </li></ul><ul><ul><li>The mountain is dangerously unstable , a tall, steep heap of loose rock held together by the force of gravity and a cubic mile of glacier ice that could be melted or shaken loose </li></ul></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 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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