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1. Volcanism

2-5. Formation of a Volcano

Magma, which originates in the partially melted asthenosphere
Rises through the lithosphere to form a magma chamber
Lavas erupt from the magma chamber through central and side vents
Accumulating on the surface to form a volcano

6. Types of Lavas

Basaltic lavas: low-viscosity mafic lavas, typically erupted at 1000^o to 1200^o C; cool to form basalt.
Rhyolitic lavas: high-viscosity felsic lavas, typically erupted at 800^o to 1200^o C; cool to form rhyolite.
Andesitic lavas: intermediate in composition and viscosity between mafic and felsic magmas; cool to form andesite.

7. Types of Basalts

Flood Basalts: thick, widespread accumulations of basalt, typically fed by fissures
Pahoehoe: a very low viscosity basaltic lava characterized by a ropy texture
Aa: a relatively low viscosity basaltic lava characterized by a jagged, blocky texture
Pillow Basalts: a basaltic lava extruded beneath the water, characterized by glassy pillows filled with crystalline basalt

8. Columbia River basalts - map

9. Columbia River basalts - photo

10. Aa and Pahoehoe lavas - photo

11. Vesicular Basalt: trapped gases form bubbles (vesicles)

12. Central America - map

13. Pryoclastic Material

Fragmentary volcanic rocks ejected into the air

14. Volcanic Bomb

15. Volcanic Breccia

16. Pyroclastic Flows

A density flow consisting of a hot (800°C), poisonous mixture of gas and pyroclastic material moving downslope at 200 km/hr.

17. Eruptive Styles and Landforms

Shield Volcano
Volcanic Dome
Cinder Cone
Composite Volcano
Crater
Caldera

18. Mauna Loa in Hawaii

19. Shield Volcano

20. Shield Volcanoes

Formed mainly of basaltic lavas
Gentle sides: ~2-10 degrees
Can be huge: up to 120 km wide!
Long duration of activity:10,000’s yrs
Eruptions usually non-violent

21. Lava Dome - photo

22. Volcanic Dome

23. Volcanic Domes

Form of viscous felsic lavas
Steep-sided and small:~100’s m wide
Grow slowly

24. Cerro Negro Cinder Cone, near Managua, Nicaragua in 1968

25. Cinder Cone

26. Cinder Cones

Formed mainly of basaltic pyroclastic material
Steep sides: ~30 degrees
Relatively small: ~ 1km wide
Short-lived: typically a single event

27. Mt Fujiyama, Japan

28. Composite Volcano

29. Composite Volcano

Mainly alternating pyroclastic deposits and andesitic lava flows
Slopes are intermediate in steepness
Relatively large: ~10-15 km wide
Intermittent eruptions over long time span: 1,000’s of yrs
Eruptions often highly explosive

30. Caldera – Crater Lake, Oregon

31. Caldera

A large depression (typically several km wide) formed by collapse of a volcano into a partially drained magma chamber
May have younger domes within it

32-35. Formation of a Caldera

Fresh magma fills a magma chamber and triggers a volcanic eruption of lava and columns of incandescent ash.
Eruption of lava and pyroclastic flows continue, and the magma chamber becomes partly depleted.
A caldera results when the mountain summit collapses into the empty chamber. Large pyroclastic flows accompany the collapse, blanketing the caldera and a surrounding area of hundreds of square kilometers.
A lake forms in the caldera. As the reidual magma in the chamber cools, minor eruptive activity continues in the form of hot springs and gas emissions. A small volcanic cone forms in the caldera.

36. Welded Tuff formed from Pyroclastic Flow Deposit

37. Phreatic Explosion – magma mixing with water

38-39. Formation of a Diatreme

40. Shiprock, New Mexico - photo

41. Fissure Eruptions

A volcanic eruption originating along an elongate fissure rather than a central vent.

42. Volcanoes along the Laki Fissure (Iceland) formed in 1783

43. Fissure Eruptions and associated Flood Basalts

44. Lahars (Volcanic mudflows)

Formed by the sudden mixing of large volumes of pyroclastic material with water (e.g. heavy rain, draining of crater lake, melting of glacier).

45. They Move Fast

Lahars can move 100+ km/hr, and can cover large areas (1,000’s of km²), and can kill large numbers of people (~25,000 in one event)

46-50. Monitoring Volcanos

Hawaii
Mount St. Helens

51. Hydrothermal Activity:

The circulation of water through hot volcanic rocks and magma
Forms fumaroles – volcanic vents emitting gases, some charged with dissolved minerals
Forms geysers – heated hydrothermal waters under pressure, that intermittently erupts at the surface
Provides the source for Geothermal Energy.

52. Sulfur-encrusted Fumarole

53. Strokkur Geyser in Iceland

54. Active Subaerial Volcanoes of the World

80% at convergent plate boundaries

55. Volcanism Associated with Plate Tectonics

56. Hot Spot Tracks – record movement of plate

57. Hawaiian-Emperor Seamount Chain - map

58. Hawaiian-Emperor Seamount Chain – age map

59. Yellowstone Hot Spot Track Formed as the North American Plate Moved WSW

60. Age of Yellowstone Calderas Track Movement of Plate over the Hot Spot

61. Types of Volcanic Hazards

62. Cumulative Deaths due to volcanic eruptions over the last 2,000 years

63. Types of Volcanic Hazards

Lava Flows:
e.g. Hawaii, 1998
Gas:
e.g. Lake Nyos (Cameroon), 1984 -1700 people killed
Ash fall:
e.g. Mt Pinatubo, 1991

64. Types of Volcanic Hazards

Pyroclastic flows:
e.g. Mt Pelee, 1902 - 28,000 killed
Lahars (mudflows):
e.g. Nevado del Ruiz, 1985 - 23,000 killed
Tsunami:
e.g. Krakatoa, 1883 - 36,417 killed

65. How bad can it be?

1815 Indonesia 92,000 died*
1822 Indonesia 5,500 killed
1826 Indonesia 3,000 killed
1883 Indonesia 36,417 killed
1902 Martinique 29,025 killed
1902 Guatemala 6,000 killed
1919 Indonesia 5,110 killed
1951 New Guinea 2,942 killed
1982 Mexico 1,700 killed
1985 Columbia 23,000 killed

66. Causes of Volcanic-related Deaths over the last 2,000 years

67-69. Location of Potential Hazardous Volcanoes in U.S.

70. Large Igneous Provinces (LIP’s)

Voluminous emplacements of predominately mafic igneous rocks formed by processes other than “normal” seafloor spreading

71. Global Distribution of LIP’s

72-76. Formation of LIP’s/Hotspot Tracks