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earthquakes chpt 8 study guide

True false 54 magma compositions are independent of

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True False 54. Magma compositions are independent of the amount of crustal rock melted and incorporated into the rising magma. True False 55. Magma rising in a subduction zone tends to get more "contaminated" with high-silica minerals than does magma rising in a spreading ridge. True False 56. If the magma cools and solidifies below the surface, it crystallizes as volcanic rocks. True False
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57. If the magma reaches the surface, it forms volcanic rocks, named for Vulcan, the Roman god of fire. True False 58. Highly fluid basaltic lava may cool with a smooth, ropy surface called pahoehoe, whereas lower temperature, slower flowing, more viscous basaltic lava commonly has a rough, blocky texture called aa. True False 59. Airborne pyroclasts have their finest grains settle down from the atmosphere first, closest to the volcano, followed by progressively coarser material at greater distances away. True False 60. If lava reaches the sea or a lake it cools rapidly into ovoid or toothpaste-looking forms called pillow lava. True False 61. When it comes to volcanic hazards, the key problem is how easily the dissolved gases can escape from the magma. True False 62. At a depth of 20 miles, basaltic rock melts at around 1400 ° C but this same rock will melt at only 1250 ° C at the Earth's surface. True False 63. Hot spots can be under the oceans, under the continents, in the center of plates, and at spreading centers. True False 64. Antarctica does not lie above any hot spots, partly explaining its massive volumes of ice. True False 65. The largest number of hot spots lie beneath the Juan de Fuca plate. True False 66. In the last 2 million years, three catastrophic eruptions have occurred at Yellowstone at about 2 million, 1.3 million, and 600,000 years ago. True False 67. The Volcanic Explosivity Index (VEI) ranges from 0 to 10. True False 68. When magma nears the surface, gases come out of solution and help cause volcanic eruption. True False 69. When gas escapes quickly and violently from lava it may produce a frothy glass full of holes left by former gas bubbles; this porous material, known as pumice, contains so many holes it can float on water. True False
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70. Because vulcanologists are aware of the potential hazards, no vulcanologist has ever been killed studying a volcano. True False 71. Transform faults have lots of associated volcanism because the strike slip motions keep a "lid" on the hot asthenosphere below, allowing it to melt. True False 72. The most abundant dissolved gas in magmas is water. True False 73. A scoria cone is likely to form if lava is low in gas content and high in viscosity. True False 74. Eruptions in Hawaii are always peaceful. True False 75. Lava domes form when high viscosity magma with low volatile content cools quickly, forming a hardened dome a few meters to a kilometer or so in height. True False 76. Hot spots occur only under oceanic plates. True False 77. Hawaiian volcanoes produce andesitic lava. True False
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Chapter 8 Volcanic Eruptions: Plate Tectonics and Magmas Key
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1. A 2. A 3. B 4. D 5. C 6. D 7. D 8. A 9. D 10. B 11. C 12. D 13. A 14. D 15. E 16. A 17. B 18. B 19. D 20. A 21. E 22. A 23. A 24. C 25. C 26. A 27. D 28. C 29. C 30. B 31. A 32. B 33. C 34. TRUE 35. TRUE 36. TRUE 37. FALSE 38. TRUE 39. TRUE 40. TRUE 41. TRUE 42. FALSE 43. FALSE 44. FALSE 45. TRUE 46. TRUE 47. TRUE 48. TRUE 49. TRUE 50. FALSE 51. FALSE 52. TRUE 53. TRUE 54. FALSE 55. TRUE 56. FALSE 57. TRUE 58. TRUE 59. FALSE 60. TRUE 61. TRUE 62. TRUE 63. TRUE 64. FALSE 65. FALSE 66. TRUE 67. FALSE 68. TRUE 69. TRUE
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70. FALSE 71. FALSE 72. TRUE 73. FALSE 74. FALSE 75. TRUE 76. FALSE 77. FALSE
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True False 54 Magma compositions are independent of the...

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