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What Controls Volcanic Eruptions?

What Controls Volcanic Eruptions?. Ch 12.2. Some eruptions are quiet…. Kilauea, Hawaii. Some eruptions are EXPLOSIVE!. Mt. Pinatubo. Montserrat. Mt. St. Helens. What Controls Volcanic Eruptions?. How much water vapor (a gas) and other gases are trapped in the erupting magma

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What Controls Volcanic Eruptions?

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  1. What Controls Volcanic Eruptions? Ch 12.2

  2. Some eruptions are quiet… Kilauea, Hawaii

  3. Some eruptions are EXPLOSIVE! Mt. Pinatubo Montserrat Mt. St. Helens

  4. What Controls Volcanic Eruptions? • How much water vapor (a gas) and other gases are trapped in the erupting magma • How much silica is contained in the magma

  5. Trapped Gases • water vapor and carbon dioxide are dissolved in magma • When magma rises to surface, gases escape because they are under less pressure • Some magma is thin and fluid- this lets gases escape easily- resulting in quiet eruption • Other magma is thick and stiff- when gases erupt it results in explosive eruption

  6. Water VaporWater may be added to magma when ocean crust rock is melted at convergent plate boundaries

  7. Silica-rich magma is called granitic/rhyolitic magma Results in explosive eruptions Ex. Soufriere Hills in Montserrat Characteristic of convergent plates Silica-poor magma is called basaltic magma Results in quiet eruptions Ex. Iceland Characteristic of divergent plates Composition of magma

  8. Basaltic magma may result in different three lava types: • Pahoehoe • Aa • Pillow (cools the fastest)

  9. Pahoehoe lava: • Hot, thin, fast flowing • harden with a relatively smooth surface • Often has a ropy or wrinkled appearance

  10. Pahoehoe lava

  11. Aa lava: • Cooler, thicker, slow moving • Hardens with a rough, jagged, sharp edge surface

  12. Pillow Lava: • Lava cools underwater • resembles stuffed pillows

  13. Explosive Magma/Lava Granitic/Rhyolitic Magma high in silica high amount of trapped gases very viscous lead to explosive type eruptions Soufriere Hills volcano-active since 1995 At what type of boundary would granitic/rhyolitic magma form? convergent boundaries

  14. Composition of magma • Andesitic magma – more silica than basaltic magma, but less than granitic magma • Common at convergent boundaries • Named after the Andes Mountains in South America • Also violent eruptions • Ex. Krakatau- one of the most violent eruptions in history

  15. Andes Mtns

  16. Krakatau 1883 Sound heard 3,000 mi away! 13,000 x more powerful than nuclear blast at Hiroshima in WWII

  17. Anak Krakatau (Child of Krakatau)

  18. Forms of Volcanoes • Depends on: • Type of magma it was formed from • Type of eruption- quiet or explosive • 3 basic types of volcanoes • Shield • Cinder cone • Composite

  19. 1. Shield volcanoes • Result of quiet eruptions of basaltic lava flows (no ash) • May form volcanic cones or fissures- long cracks that result if flood basalts (Ragged Mtn, Lamentation Mtn) • Ex. Hawaiian Islands and the Columbia Plateau of Northwest US

  20. Shield volcanoes Mauna Kea, Hawaii

  21. Shield volcanoes Mauna Loa, Hawaii

  22. Shield volcanoes

  23. 5 Shield volcanoes make up the island of Hawaii

  24. Fissure eruption

  25. Common at divergent plate boundaries, mid-ocean ridges Fissure eruptions

  26. Columbia Plateau

  27. 2. Cinder Cones • Small base, steep-sided, loosely consolidated • Up to 1000 feet tall • Life span of a few years • Commonly built from solidified rock thrown through the air called tephra • Has violent eruptions, dangerous when close

  28. 2. Cinder Cone Volcanoes Paricutin, Mexico (1943-1952, newest volcano in Western Hemisphere, 1000 killed)

  29. Cinder Cone Volcanoes Paricutin

  30. Cinder Cone Volcanoes Pu'u ka Pele on flank of Mauna Kea volcano, Hawaii

  31. Cinder cone example: Paricutín, Mexico 1943

  32. Cinder Cone Volcanoes

  33. Composite Volcano (aka stratovolcano) • most beautiful, but most deadly • characteristic shape • made of alternating layers of lava and tephra- periods of quiet, then explosive eruptions Mt. Fuji, Japan- one of the most photographed volcanoes in the world because of its near perfect symmetry Ex. Mt. St. Helens

  34. Composite Volcanoes

  35. What are the three types of magma in order from least viscous to most viscous? • a. Basaltic • b. Andesitic • c. Granitic

  36. Tephra • Names are based on size: • Ash • Lapilli/Cinders • Bombs/Blocks

  37. Volcanoes Volcanoes eject different types of material. This material is known as tephra or pyroclastic material. There are 3 main types: Ash-less than 2 mm in diameter Lapilli/cinders-2mm-64 mm in diameter Blocks orBombs-larger than 64mm

  38. Ash

  39. Lapilli/Cinders Mt Pinatubo, Philippines 1991

  40. Bombs

  41. Blocks

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