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
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. Viscosity

14. Volcanic materials
A. Lava
Molten rock
Si affects viscosity

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

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

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

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

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

22. 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

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

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

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

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

27. II. Volcanic materials B) Effects on global climate
CO2 – Greenhouse gas
SO2 – Blocks sunlight

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

29. III. Volcanic Landforms

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

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

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

33. A. Volcanic cones 1) Shield volcanoes
Tall volcanoes –3 or 4 miles tall
Wide base – Diameter of ten of miles

34. A. Volcanic cones
Mauna Loa volcano, Hawaii

37. 1996

38. 1996

39. 1996
1997

49. A. Volcanic cones 2) Cinder cones – Smallest volcanic cone
Layered ash and cinders
Ex: El Paricutin

50. A. Volcanic cones 2) Cinder cones Short, narrow cone, Steep sides
Violent eruptions

51. A. Volcanic cones
Lassen National
Monument, CA

52. Paricutin, Mexico (1940s)

60. A. Volcanic cones 3) Composite or stratovolcanoes –
Layered ash, lava, and mud
Intermediate to felsic lava
Steep sides, due to lava’s high viscosity

61. A. Volcanic cones 3) Composite or stratovolcanoes –
Tall volcanoes – 1 to 2 miles high
Violent eruptions

62. Mount Pelée –
St. Martinique (1902)

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

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

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

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

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

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

92. C) Calderas
Ex: Crater Lake, OR

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

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

105. IV. Volcanic hazards

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

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

108. IV. Volcanic hazards B) Nuee Ardentes (Glowing Ash flows)
Clouds of dense gas and debris
French for “glowing cloud”
High speeds and high temperatures

109. IV. Volcanic hazards How does a Nuee Ardente form? Volcano erupts
Hot debris rises
Gravity takes over

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

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

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

114. IV. Volcanic hazards D) Lava flows Least dangerous
Lava flows slowly (<10 mph)
Dangerous to property

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

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

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

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

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

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

121. 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

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