1. Volcanoes!!

2. What is a Volcano?

3. Volcano - A Volcano is an opening in the Earth’s surface through which molten material or volcanic gases are erupted.

4. A volcano can either be a classic volcanic cone…..

5. Mt. St. Helens, pre-1980

6. Mount Ranier

7. a crack in the ground, through which lava erupts……

8. Or a simple volcanic vent.

9. How Magma Rises
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10. Where are volcanoes located?

11. Major Volcanoes Around the World

12. Volcanic Settings

13. How and Where Volcanoes Form
Volcanic activity takes place primarily at subduction boundaries,
4. Some of the magma reaches Earth’s surface, and volcanoes form on the overriding continental plate.
1. Water in the subducted rock is released into the asthenosphere.
Oceanic lithosphere
Continental lithosphere
Asthenosphere
3. The magma is less dense than its surroundings, so it rises.
2. The water lowers the melting temperatures of materials in the asthenosphere, leading to magma formation.

14. Ocean-
Continental
Subduction
Pacific Northwest Volcanoes

15. Ocean-
Ocean
Subduction

16. Ocean-
Ocean
Subduction

17. Diverging Boundary Volcano

19. Hot Spot Volcano

20. How and Where Volcanoes Form
Magma and volcanoes also form at hot spots.
Kauai
Oahu
Direction of Plate Movement
The Hawaiian Islands formed over a hot spot.
Molokai
Lanai
Maui
Hawaii

21. Major Hotspots of the World

22. Plate Tectonics and Magma Generation
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23. Tectonic Settings and Volcanic Activity
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24. Volcanoes are classified as either Active, Extinct or Dormant

25. Active

28. Dormat
Mt. Ranier

29. Vesuvius

30. Extinct

32. Magma and Erupted Materials
Parameters of volcanism:
Viscosity
Chemistry of Magma
Gases within the magma
Water content of magma

33. Magma and Erupted Materials
Viscosity: Viscosity is a measure of how thick (viscous) and sticky a liquid is.
VOCABULARY
viscosity
lava
pahoehoe aa
pillow lava
pyroclastic material
pyroclastic flow

34. Types of Magma

35. Felsic Magma Characteristics: -light in color
-high viscosity: means it is very
thick and flows very slowly.
-Associated with composite type volcanoes and continential
hotspots
-Found along continental-ocean subduction boundaries.

37. Mafic Magma Characteristics: -dark in color
-low viscosity: means it is thinner and flows much faster
-Associated with shield volcanoes, rift zones, and oceanic hotspots
-Found at divergent
boundaries and oceanic hotspots

39. Gases in Magma Water Vapor Carbon-Dioxide Carbon Monoxide
Sulfur-Dioxide
Hydrogen-Sulfide

40. Types of Lava

41. Pahoehoe Lava

44. Aa Lava
Aa Lava

47. Pillow Lava

49. Types of Lava Fragments

50. Ash

51. Ash Layers

53. Pyroclastic Rock- Tephra

55. Pyroclastic Rock- Pumice

56. Cinder

58. Bombs

60. Blocks
Blocks

61. Volcanic Blocks

62. Pyroclastic Flows

63. There are three types of volcanic cones:
Cinder
______ – explosive eruptions, small but steep slopes, pyroclastics.
_______ – non-explosive eruptions, fluid basaltic lava, gentle broad slopes.
_________ – alternating between lava and pyroclastics, explosive and non-explosive eruptions, steep and tall.
Shield
Composite

64. Volcano Types
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65. Volcanic Landforms Volcanoes
VOCABULARY
A volcano’s shape and structure depend on how it erupts and what materials are released.
shield volcano
cinder cone
composite volcano
Shield volcanoes are formed by basaltic lava that flows long distances before hardening.
lahar
caldera
Shield Volcano
lava plateau

66. Shield and Composite Volcanoes

67. Volcanic Landforms Volcanoes
Cinder cones are formed when molten lava is thrown into the air from a vent and breaks into drops. These drops harden into cinders that form a steep cone around the vent.
Cinder Cone

68. Volcanic Landforms Volcanoes
Composite volcanoes are formed by layers of pyroclastic materials and lava that have erupted in the past.
Composite Volcano

69. Composite volcanoes

70. Debris Avalanche and Eruption of Mount St. Helens, Washington
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71. Nuee ardente: pyroclastic flow, of searing superheated gas and incandescent volcanic ash and dust
Mount Pelee, on the Carribean island of Martinique, 1902 eruption. All but 2 of the more than
20,000 people in the town of St. Pierre were killed.

72. Lava Plateau

73. Volcanic Landforms Volcanoes
A caldera is a large crater-shaped basin that forms when the top of a volcano collapses.

74. Formation of Crater Lake
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75. EFFUSIVE ERUPTIONS Generally at hots spots, spreading centers
Mantle comes directly to surface
Hot lava; low viscosity, very mafic, flows easily, gases escape easily
Forms shields, flood basalts

76. EXPLOSIVE ERUPTIONS Found at subduction zones
Magma low temp (800 degrees C), high viscosity, does not flow easilty, more felsic mineralogy, gases trapped, hard to predict explosions
Forms composite volcanoes, cinder cones, calderas, aerial bombs, nuee ardente gas flows, very destructive