1. THE ROCK CYCLE

2. VOLCANISM

3. I. Introduction
From: Roman god of fire, Vulcan

4. I. Introduction From: Roman god of fire, Vulcan What is a volcano?
A conical mountain formed around a vent where lava, pyroclastic materials, and gases are erupted.

5. I. Introduction
B. Volcanic activity:
Active
Dormant
Extinct

6. B. Volcanic Activity 1. Active volcanoes
activity in the last few centuries
Ex: Vesuvius, 79 A.D.
(50 times in 2000 yr)
Ex: Mt. St. Helens (1980)

7. B. Volcanic Activity 2. Dormant volcanoes
“quiet” for the last hundred to thousands of years, but still have potential to erupt.
Mt. Rainier

8. B. Volcanic Activity 3. Extinct volcanoes
No eruption in historical times
No signs of erupting again

9. Introduction C. Volcano Distribution
Most volcanoes occur in one of three areas:
Circum-Pacific (i.e. The Ring of Fire)
60%
Mediterranean
20%
Spreading centers (Divergent boundaries)
10 – 15%

10. Volcano Distribution

11. II. Volcanic materials
Three types of material expelled from volcanoes

12. Volcanic materials
A. Lava (“the liquid”)
Molten rock

13. Volcanic materials A. Lava Silica affects viscosity
Molten rock
Silica affects viscosity
Viscosity is resistance to flow

14. II. Volcanic materials A. Lava 1) Pahoehoe lava Basaltic lava
Low viscosity

15. II. Volcanic materials A. Lava 1) Pahoehoe lava Basaltic lava
Low viscosity
Cools moderately slowly
Ropelike appearance

16. II. Volcanic materials A. Lava 2) Aa lava (pronounced aa-aa)
Basaltic lava
Higher viscosity
Solidifies while flowing
Angular pieces

17. II. Volcanic materials A. Lava 3) Pillow lavas
Lava extruded underwater
Cools and contracts
Spherical masses
Ocean floor

18. II. Volcanic materials A. Lava (“the liquid”)
B. Ash and pyroclastic material (“the solid”)
Airborne material ejected by a volcano
Classified based on size:

19. B. Ash and pyroclastic material (“the solid”)
* Volcanic ash
Fine ash - <0.06mm
Coarse ash – 0.06mm to 2mm
Composition = rock, mineral, and volcanic glass

20. B. Ash and pyroclastic material (“the solid”)
* Cinders
2 mm and 64 mm
Composition - same as ash
Hazardous when falling

21. B. Ash and pyroclastic material (“the solid”)
C) Bombs
Larger than 64mm
Molten rock solidifies in the air
Shapes vary

22. II. Volcanic materials C. Volcanic gases (“the gases”) Volatiles
H2S – Hydrogen sulfide
H2O – Water vapor
CO2 – Carbon dioxide
N2 – Nitrogen
HCl – Hydrochloric Acid
SO2 – Sulfides

23. II. Volcanic materials A) Determines violence of an eruption
High amount of gas = violent eruptions
Violent eruptions = felsic magmas (high silica)
High viscosity magma traps gas
Expansion is prevented, pressure builds

24. II. Volcanic materials B) Effects on global climate
CO2 – Greenhouse gas
Particulates – Blocks sunlight

25. II. Volcanic materials Hazards to humans Clouds of CO2 get released
Travels across the ground

26. III. Volcanic Landforms

27. III. Volcanic Landforms
An erupting volcano will produce a number of distinct landforms including:
A. Volcanic cones
B. Flood basalts
C. Calderas

28. A. Volcanic cones
Three types of volcanic cones:

29. A. Volcanic cones 1) Shield volcanoes Multiple layers of basaltic lava
Shallow sides due to magma’s low viscosity
Gentle eruptions
Wide base

30. A. Volcanic cones
Mauna Loa volcano, Hawaii

31. A. Volcanic cones 2) Cinder cones – Smallest volcanic cone
High viscosity
Narrow
Steep sides
Violent eruptions shoot material straight up

32. A. Volcanic cones
Lassen National
Monument, CA

33. A. Volcanic cones 3) Composite or stratovolcanoes –
Layered ash, lava, and mud
Intermediate to felsic lava
Medium steepness, due to lava’s medium viscosity
Between a shield and cinder cone

34. A. Volcanic cones
Mt. St. Helens, WA

35. III. Volcanic Landforms B) Flood basalts
Large outpourings of basaltic lava
Multiple, quiet eruptions

36. B) Flood basalts
A portion of the Columbia Flood Basalts in WA

37. III. Volcanic Landforms
C) Calderas
Large depressions (> 1km) from violent eruptions
Ugashik Caldera, AK
Yellowstone

38. C) Calderas Two methods of formation:
Volcano rapidly empties its magma chamber, and support is lost

39. C) Calderas Method 1 (cont.):
Overlying material collapses into magma chamber
Caldera forms

40. C) Calderas
Ex: Crater Lake

41. C) Calderas Two methods of formation:
Volcano blows its top,
leaving behind a void
Inside the cone.

42. C) Calderas Two methods of formation:
Volcano blows its top,
leaving behind a void
Inside the cone.

43. IV. Volcanic hazards

44. IV. Volcanic hazards
Lahars (hot mud flows)

45. IV. Volcanic hazards Lahars Sources of water Melting ice caps
Excess rainfall

46. IV. Volcanic hazards B) Pyroclastic flows
Clouds of dense gas and debris
French for “glowing cloud”
High speeds and high temperatures

47. IV. Volcanic hazards How does a pyroclastic flow form? Volcano erupts
Hot debris rises
Gravity takes over

48. IV. Volcanic hazards How does a pyroclastic flow form?(cont’d)
Debris descends rapidly (200 mph)
Flows down mountain slopes
Travel up to 80 miles

49. IV. Volcanic hazards C) Tsunamis Wave generated by volcanic explosion
Japanese for harbor wave

50. IV. Volcanic hazards Tsunamis are extremely hazardous
Travel vast distances
Strike with short notice
Krakatoa (1883) - 36,000 people died

51. IV. Volcanic hazards D) Lava flows Least dangerous
Lava flows pretty slowly
Dangerous to property

52. V. Predicting Eruptions
Why try to predict eruptions?
Minimize damage
Minimize loss of life
Four ways to predict an eruption:

53. V. Predicting Eruptions
1) Harmonic tremors
Small earthquakes
From moving magma
Last for hours

54. V. Predicting Eruptions
2) Increased gas emissions
CO2
SO2
H2S
Large tracts of healthy forests die off

55. V. Predicting Eruptions
3) Changes in mountain shape
Pressure from the magma deforms the mountain
Detected by tiltmeters

56. V. Predicting Eruptions
Tiltmeter
Tiltmeter measures ground tilt
Stable ground = zero tilt
Change from zero indicates shape change

57. V. Predicting Eruptions
Mt. St. Helens and the orange line

58. V. Predicting Eruptions
4) Observe material from past eruptions
Geologists map out past:
Lahars
Lava flows
Count number of past eruptions
Date each eruption
Calculate periodicity

59. VI. Benefits of Volcanoes
Soils
Energy from heat
Rock (Pumice)
Gases for industry