2. Geology 12 Presents

3. Chp 4 Volcanics (& Plutonics) Intrusive igneous body = pluton = when magma intrudes into and solidifies in the crust. They are later exposed due to weathering & erosion 2 types: Concordant & Discordant A: Concordant: boundaries of pluton parallel to layers in country rock. sills & laccoliths

7. A: concordant features: intrusion runs parallel to bedding 1. sill: usually <1 m thick (but up to 300 m thick Parallel to bedding structures Has inclusions of country rock & contact metamorphism in top & bottom No vessicles (bubbles) –Ex: Palisades of New York

8. 1. Sill:

9. 2. Laccolith: mushroom top sill where overlying rock is pushed up “zit” –Ex: Black Hills, S.D.

10. Laccolith : concordant

12. Black Hills, SD

15. B: Discordant: boundaries of intrusion cut across layering of country rock. –Dikes, pipes, stocks/batholiths

16. 1. Dikes: 1-2 m thick (but some cm to 100s of m thick

17. Dike: discordant Volcano

18. Dike: discordant

19. Ship Rock, AZ. Volcanic neck

20. 2. Volcanic Pipe: solid lava conduit from magma chamber to surface –Mined for diamonds in northern Canada. Volcano Neck After Before Pipe Magma Chamber

21. Volcanic Pipe: discordant Ekati Mine, NWT

22. Volcanic neck

23. Devils Tower, WY.

24. 3. Batholith: largest intrusive body with >100 km 2 of exposed surface area –Stock: <100 km 2 of exposed surface area –Usually granite Stock Batholith Xenolith Before After

25. Batholith: discordant

28. Chief

29. Stock: discordant

30. Extrusive igneous body: structures created by magma -> lava solidifing (Volcanics) on the Earth’s surface. 550 active volcanoes (60% on Ring of Fire, 20% in Mediterrean, rest mainly on divergent boundaries) Emit many gasses: H 2 O (50-80%), CO 2, N 2, SO 2, H 2 S (+ some CO, H 2,Cl 2 ).

31. Types of Lava: Type of Lava Volcano Type Location Viscosity Colour Felsic/silisic composite convergent thick/hi light dome ocean\cont intermediate cinder cone ocean\ocean Mafic shield divergent thin/lo dark basalt flood cinder cones hot spots Explosive &

32. Subduction: Oceanic\Cont’l

33. Subduction: oceanic\oceanic

34. Divergent

35. Hot Spots

36. Lava Flows & Pyroclastic Material fire + pieces blown out of volcano A: Lava Flows: 1.Pahoehoe: ropey, cow pie lava From thin mafic Play pahoehoe movie

37. Lava Flows: Pahoehoe

38. Ford Tough

39. 2. Aa: rough, jagged, angular blocks of lava –As lava freezes, it is being moved and breaks into pieces like glass.

40. Lava Flows: Aa

42. 3. Columnar Jointing: lava cools, contracts and splits at 60’ angles into hexagonal columns 3. Columnar Jointing: lava cools, contracts and splits at 60’ angles into hexagonal columns Mainly mafic lava Mainly mafic lava

43. Lava Flows:Columnar Jointing

44. 4. Pillow lava: blobs of lava quickly freeze underwater into “pillows ”

45. Lava Flows: Pillow Lava

46. B: Pyroclastic Material = Tephra = lava ejected into air 1. Ash: < 2mm –Most common pyroclastic –Welds to form tuff –Can be ejected 2 ways: A) Ash Fall: blown high into atmosphere & may travel 1000s of km before settling –Can cool climate for years (ice age?) B) Ash Flow= Nuee Ardente = Pyroclastic Flow: horizontal blast of ash and gasses –+500C at 800 km/h –Mt St Helens, Martinique

47. Pyroclastics: Ash

49. Pyroclastics: Ash Fall

50. Pyroclastics: Ash Flow Animation

51. 2. Lapilla: 2-64mm = pebble size

52. Pyroclastics: Lapilla

53. 3. Blocks: solid chunk of igneous rock >64mm blown out of volcano

54. Pyroclastics: Blocks

55. 4. Bombs: blob of hot molten lava >64mm that is ejected, and partially freezes in flight. molten solid

56. Pyroclastics: Bombs

57. Volcano: conical mountain formed around a vent Crater: depression near summit of volcano

58. Caldera: huge depression when most of volcano falls back into magma chamber

61. CO 2 being emitted with a pipe from a lake in a dormant volcano in Africa

62. Types of Volcanoes 1. Composite/Strato: composed of layers of pyroclastics and lava flows –Andesitic rock usually (intermediate lava) –Ex. Mt. Baker, Mt. Vesuvius, Mt Fuji Lava Ash 30’

63. Volcano: Composite/Strato

64. Mt. Rainier

65. Mt. St. Helens

66. Fuego, Mexico

67. Mt. Jefferson

68. Mt. Washinton

69. Mt. Shasta

70. Three Sisters & Black Butte

71. Lahar: mudflow of ash & water –Kill 1000s –Tacoma is built on old lahars! –*Lahars and Pyroclastic flows pose the greatest human danger from volcanoes

72. Volcano: lahar mud flow

73. 2. Lava Dome: very, thick felsic/silisic lava moves up slowly under immense pressure –Ex: Lassen Peak, CA, inside of Mt. St. Helens Old volcano Dome

74. Lassen Dome, CA

75. Volcano: Lava Dome

76. 3. Cinder Cones: short-lived “baby volcanoes consisting of just pyroclastics –Form from initial eruption –Up to 400 m high 33’

77. Volcano: Cinder Cone

79. 4. Shield: shallow sloped consisting of many low-viscosity mafic lava flows –Largest volcanoes on Earth –Ex: Hawaii (10 km high = BIG) 10’

80. Volcano: Shield

82. 5. Basalt Flood/Basalt Plateau: large flows of low-viscosity mafic lava that flow from long fissures (crack), rather than a single vent. –Result of divergent boundaries

83. Volcano: Basalt Flood

87. One flow Cumulative flows in Washington are over 1 mile thick One flow

89. Melting Rock Mantle rock is solid, magma is only present under certain conditions Mantle rock is solid, magma is only present under certain conditions Factors that affect melting include Factors that affect melting include Temperature Temperature Pressure Pressure Volatiles (water, gas) Volatiles (water, gas)

90. Temperature Geothermal gradient, temperature increases 25 celsius every km depth Geothermal gradient, temperature increases 25 celsius every km depth Melting temperature of rocks at the surface is between 750-1000celsius Melting temperature of rocks at the surface is between 750-1000celsius Different minerals melt at lower temperatures, this produces a partial melt of mantle and crust rocks Different minerals melt at lower temperatures, this produces a partial melt of mantle and crust rocks

91. Pressure Pressure increases with depth, causes a higher melting temperature Pressure increases with depth, causes a higher melting temperature

92. Why Magma Rises 1. Forceful Ejection: magma moves from high pressure at depth to low pressure at the surface 2. Stoping: displacement of magma by country rock (i.e. xenoliths) pushes magma up (like placing ice cubes in a glass of water)

93. Stoping

95. Explosiveness of a volcano is dependent on: 1. viscosity of magma: high viscosity slows the escape of gases which expand greatly near the surface 2. “stickiness” of magma = “corking effect”. The stickier, the more pressure it requires to erupt so when it does erupt… Higher silica increases both viscosity & stickiness

96. Do Lab 4-1 Igneous Rock ID Do Lab 4-1 Igneous Rock ID Do WS 4.1 Do WS 4.1 Do Chps 3-4 Review WS Do Chps 3-4 Review WS