1. VOLCANISM
The Walker School
Geology

2. Volcanism is a Constructive Process
 Atmosphere
 Water
 Crust
Painting of Early Earth’s Volcanism

3. Current Volcanism
 Iceland
 Hawaiian Islands
 Azores
 Galapagos Islands
Volcanism at Hawaii’s National Park

4. Notable Volcanic Eruptions
Table 5-1, p. 135

5. Mount Vesuvius Continues to Errupt
Fig. 5-1, p. 134

6. Maps of the World’s Major Volcanoes
•550 Are Currently
Active
•About 1 dozen
are erupting at
anyone time
•Responsible for
extrusive igneous
rock

7. Viewing Volcanoes in Google Earth

8. Basic Volcanic Structure

9. Pyroclastic Materials
 Blocks
 Bombs
 Lapilli
 Ash
Size
Volcanic Bomb

10. Lava Tubes at Volcanic National Park, HI
Lava Tube
in Hawaii
Fig. 5-3a, p. 137

11. Lava Textures
Pahoehoe (pah-hoy-hoy) is Aa (ah-ah) is characterized by a
characterized by its smooth and rough, clinkery surface and is
often ropey or wrinkly surface and what most viscous and hot lava
is generally formed from more flows look like.
fluid lava flows.
Fig. 5-4a, p. 137

12. Lava Composition
 Felsic Lava: high percentage (>63%) of silica, and
trapped gasses; highest viscosity, lowest temperatures
 Andesitic Lava: (52-63%) of silica
 Mafic Lava: (45-52%) of silica + high percentage of
Magnesium (Mg); typically occur at subduction zones
 Balsitic Lava: (45-52%) of silica + high percentage of
Iron (Fe); typically occur at oceanic divergent pages
 Ultramafic Lava: (=<45%) of silica; lowest vicsosity,
highest temperatures

13. Columnar Jointing at Devil’s Post Pile
National Monument, CA
Fig. 5-5b, p. 138

14. Inversion of Topography
 1. Lava flows into the
valley
 2. Lava cools and
crystallizes, forming
extrusive igneous rocks.
 3. Areas adjacent to
the flow erode more
easily then the flow
 4. Over time, an
inversion is produced.
Fig. 5-6ab, p. 139

15. Craters of the Moon National Monument, ID
http://www.nps.gov/crmo/
Fig. 5-3b, p. 137

16. VOLCANIC TYPES

17. Types of Volcanoes

18. Fig. 5-18, p. 149

19. Plutonic Bodies

20. Formation of a Caldera
Fig. 5-9a-d, p. 142

21. Crater Lake, OR Caldera
Caldera Floor of Crater Lake
Wizard Island, Crater Lake, OR

22. Shield Volcanos
Fig. 5-10a, p. 143

23. Shield Volcano, Mauna Loa, HI
•Low Viscosity Basalt Flows
•Lava fountains
•Most common in ocean basins

24. Cinder Cones
Fig. 5-11a, p. 144

25. Cinder Cones, Mojave Desert, CA
•Eruptions are short-lived.
•Large, bowl-shaped craters.
•Ash builds up rapidly.
•Few lava flows.
•Lava flows typically from base of cone.

26. Stratovolcanoes (Composite Cones)
Fig. 5-13a, p. 146

27. Stratovolcano, Mt. Rainier, WA
From Space
•Composed of layered sills.
•Lahars, or volcanic mud flows are common.
•Have steep slops near summit.
•Lava flows from andesite.

28. Lahar Flows, Mt. Pinatubo, Philippines
Mt. Pinatubo
from Space
Fig. 5-14a, p. 146

29. Lava Domes
Fig. 5-15b, p. 147

30. Lava Dome, Mt. St. Helens, WA
•Composed of felsic magma.
•Formed from intermediate magma forced up under great pressure.
•Highly unstable, will collapse under weight of rock.
Fig. 5-15a, p. 147

31. Mt. Saint Helens Eruption
http://www.youtube.com/watch?v=bgRnVhbfIKQ

32. VOLCANIC ERUPTIONS

33. Types of Erruptions

34. Fig. 5-17, p. 148

35. Fissure Eruptions
 Generated along a
linear fracture
 Composed of low-
viscosity melt
 Commonly occur along
divergent plate
boundaries
 Also common on the
edges of large Fissure eruption in Iceland
volcanoes.
 Produces a curtain of
fire.

36. Columbia River Basalt Plateau
Fig. 5-19, p. 150

37. Volcanic Explosive Index

38. Primary Effects of Volcanoes
 Pyroclastic Flows
 Fumaroles
 Landslides
 Ash Fall
 Earthquakes
 High Temperatures

39. Secondary Effects of Explosions
 Suffocation from Ash
 Asphyxiation from Volcanic Gasses
 Tsunamis
 Temperatures Decreases

40. Environmental Effects
 Involved in the formation of continental crust and
offset weathering and erosion
 Provide nutrient rich soils
 By trapping clouds at their peaks, water for
agriculture
 Agriculture based cultures are attracted to their
bases

41. Volcanic Gasses
 Water Vapor
 Carbon Dioxide
 Nitrogen
 Sulfur Dioxide
 Hydrogen Sulfide
 Carbon Monoxide
 Hydrogen
 Chlorine
Gasses emitted from fumaroles at the Sulfur Works in
Lassen Volcanic National Park, CA
Fig. 5-2, p. 136

42. Effects of Volcanoes on Climate
 Nucleation, condensation, and sedimentation of aerosols (acid rain)
 Change in Albedo from ash cloud
 Tropospheric cooling from the addition of sulfur to the stratsophere
 Ozone destruction through the formation of atomic chlorine

43. SUPER ERUPTIONS

44. Supereruptions
http://www.pbs.org/wgbh/nova/megavolcano/about.html

45. Discovery Questions
 What does it take to be classified as a super
eruption?
 When did the last one occur? Why is their
controversy about the date?
 What would be the primary effects of such an
eruption?
 For those who survived the initial eruption, what
would happen in the following months, or years?
 How did the Toba explosion effect the evolution of
humans?

46. DISTRIBUTION &
MONITORING

47. Distribution of Volcanoes
 Circum-Pacific
Belt (60%)
 Mediterranean
Belt (20%)
 Mid-Oceanic
Ridges (20%)
 More common along both divergent than convergent plate boundaries.
 Mainly composed of intrusive magma flows.
 Composed of mafic magma that forms beneath spreading plates.
 Pyroclastic materials are not common because lava is fluid.
 Water pressure prevents gasses from expanding and escaping.
Fig. 5-20, p. 151

48. USGS Volcano Hazards Program
http://volcanoes.usgs.gov/

49. Alaska’s Volcano Observatory
http://www.avo.alaska.edu/

50. Alaska’s Volcanoes

51. Cascade Volcano Observatory
http://vulcan.wr.usgs.gov/

52. The Cascade Range

53. Lassen Peak, CA
 Largest Lava Dome in the World

54. Lassen Peak Diagram
Concept Art, p. 154

55. Mid-Atlantic Ridge & Iceland

56. Formation of Surtsey Island, Iceland
http://www.youtube.com/watch?v=4MmX_i7S9u4

57. Important Monitoring Techniques
Fig. 5-23, p. 159

58. Fumarole Gas Monitoring
 Chemically-selective sensors
for SO2 and CO2 measure
gas concentrations and a wind
sensor measures wind speed
and direction.
 Data from solar-powered
stations are transmitted to
GOES geostationary satellite
and then down to
observatories every 10
minutes, providing near real
time data on degassing of
volcanoes

59. Ground Deformation Monitoring
 Paint
 Electronic Distance Meters
 determine the horizontal movements
that occur on active volcanoes
 Tiltmeters
 leveling surveys to measure vertical
motions
 Global Positioning Systems
 allows us to measure horizontal
motions much more accurately and
conveniently, and also to estimate
vertical motions in the same survey

60. Remote Sensing
 The Advanced Very High
Resolution Radiometer (AVHRR)
is a space-borne sensor
embarked on the NOAA family
of polar orbiting platforms.
 The primary purpose of these
instruments is to monitor clouds
and to measure the thermal
emission (cooling) of the Earth.
 The main difficulty associated
with these investigations is to
properly deal with the many
limitations of these instruments,
especially in the early period
(sensor calibration, orbital drift,
limited spectral and directional
sampling, etc).

61. WHAT ARE BLACK
SMOKERS?

62. Hydrothermal Vents
 Distributes heat and
drives water circulation
in the ocean through
convection
 Provides energy source
in the form of hydrogen
sulfide to benthic
chemotrophs
 Distributes minerals and
influences the
composition of the ocean

63. Hydrothermal Plume
White
Black smoker smoker
Sulfide
deposit
Tube worms
Magma White clam
White crab

64. Location of Major Vent Systems

65. Learn More About Vents
http://www.divediscover.whoi.edu/vents/index.html

66. Hydrothermal Vent Chemistry