2. Learning Objectives
Explain the relationship of volcanoes to plate tectonics.
Identify the different types of volcanoes and their associated features.
Locate on a map the geographic regions at risk from volcanoes.

3. Learning Objectives, cont.
Describe the effects of volcanoes and how they are linked to other natural hazards.
List the potential benefits of volcanic eruptions.
Discuss how humans can minimize the volcanic hazard.
Recommend adjustments we can make to avoid death and damage from volcanoes.

4. Eyjafjallajökull 2010 Eruption
Iceland home to more than 30 active volcanoes
Volcanic eruption in April 2010
Ash plume 9.5 km (~6 mi) high
Caused shutdown of airspace throughout Europe
Largest aerial closure since WWII
Increased seismic activity in December 2009
Future eruptions
2010 eruption was small taste of what could happen if the more explosive Katla erupts

5. Volcanic Ash Shuts Down Air Travel

6. Fire and Ice

7. 5.1 Introduction to Volcanism
Volcanic activity is directly related to plate tectonics
Most volcanoes are near plate boundaries
Approximately 2/3 of active volcanoes within “Ring of Fire”
At plate boundaries, magma is created
Magma is molten rock
Lava is magma on the Earth’s surface
Volcanoes form around a vent
Not all volcanoes are the same
Different processes in formation
Depends on tectonic settings

8. The “Ring of Fire”

9. How and Where Magma Forms
Most magma come from the asthenosphere
Weak layer of rock that is close to melting temperature
Three principal magma generating processes
Decompression melting
Pressure exerted on hot rock is decreased
Divergent plate boundaries, continental rifts, and hot spots
Addition of volatiles
Chemical compounds that lower the melting temperature of the rock
Subduction zones – responsible for “Ring of Fire”
Addition of heat
Induces melting if temperature exceeds melting temperature
Continental hot spots

10. Magma Formation

11. Magma Properties
Described by silica content and amount of dissolved gasses
Three types of magma based on silica content (low to high)
Basaltic, andesitic, and rhyolitic
Magma less dense than surrounding rock
Rises toward the surface
Accumulates in magma chambers
Composition changes
Viscosity
Volatile content

12. Magma Properties, cont. Viscosity Resistance to flow
Affected by temperature and composition
As magma cools, viscosity increases
As silica content increases, viscosity increases
Affects
The flow of lava
Shape of resulting volcano
Correlated to the volatile content

13. Magma Properties, cont. Volatile content
Determines how explosive the eruption will be
High concentration of dissolved volatiles will explode violently
Volatile-poor magma results in effusive eruptions
Volatile content increases with increasing silica content
Pyroclastic debris
Volcanic materials (like ash) that are explosively ejected

14. Volcano Characteristics

15. 5.2 Volcano Types, Formation, and Eruptive Behavior
Volcanoes vary greatly
Size, shape, composition
Number of eruptions in formation
How and where magma is formed
Amount of magma evolution
Volatile content
Viscosity and volatile content still primary control of eruption explosiveness
Volcanic explosivity index (VEI)
Relative scale to compare exlopsions

16. Volcano Characteristics

17. Volcanoes and Eruption Types

18. Volcanic Explosivity Index (VEI)

19. 5.2 Volcano Types, Formation, and Eruptive Behavior, cont.
Stratovolcanoes
Known for beautiful conical shapes
Result of high viscosity magma
Lava does not flow far resulting in steep sides
Mixture of explosive activity and lava flows
Produce combination of lava flows and pyroclastic deposits
Also called composite cones
Can be extremely explosive
Responsible for over 80% of eruptions
Responsible for most of the death and destruction
Common in the “Ring of Fire”
Examples: Mount St. Helens and Mount Rainer in United States, Mount Fuji in Japan

20. Stratovolcano

21. 5.2 Volcano Types, Formation, and Eruptive Behavior, cont.
Lava Domes
Small dome with steep sides
Often form in the vent of a stratovolcano after an explosive eruption
Can grow in single event or over decades
Made from highly viscous magma
Exhibit highly explosive eruptions
Common in the “Ring of Fire”
Examples: Mount Lassen in CA, Mt. Unzen dome in Japan

22. Lava Dome

23. 5.2 Volcano Types, Formation, and Eruptive Behavior, cont.
Shield Volcanoes
Largest volcanoes in the world
Thin lava flows build up volcano with gentle slopes
Wider than they are tall
Still among tallest mountains on Earth (measured from bases)
Associated with basaltic magma
Low viscosity, low volatile content
Gently flowing lava with non-explosive eruptions
Develop a cladera
Common at hot spots in the oceanic lithosphere and divergent plate boundaries, continental rifts
Hawaiian Islands, Iceland, and in the East African Rift
Examples: Mauna Loa and Kilauea in Hawaii

24. Shield Volcano and Volcano Dimensions

25. 5.2 Volcano Types, Formation, and Eruptive Behavior, cont.
Cinder Cones
Cone shaped with summit crater
Built from an accumulation of tephra
Small pieces of black or red lava
Formed when lava meets groundwater
Associated with basaltic eruptions
Low to intermediate explosivity
Also called scoria cones
Common on larger volcanoes, normal faults, or along cracks and fissures
Examples: SP Crater in AZ, Parícutin in Mexico, Eldfell in Iceland

26. Cinder Cone

27. 5.2 Volcano Types, Formation, and Eruptive Behavior, cont.
Continental Caldera
Large summit depression
Collapse of the land surface or volcanic edifice
Associated with rhyolite eruptions
Violent explosions
ultra-Plinian extrude a great deal of pyroclastic debris on mainly ash
Largest known as the supervolcanic type
Very rare
Examples: Mount Mazama (Crater Lake), Yellowstone caldera

28. Large Calderas Form by Explosion and Collapse

29. Crater Lake Caldera

30. Ash Fall Hazard

31. 5.3 Geographic Regions at Risk from Volcanoes
Direct volcanic risk
Ring of Fire: surrounds Pacific Ocean basin
Hot spots: Hawai’i and Yellowstone Park
Mid-ocean ridges: Iceland
Rift valleys: East Africa
Indirect volcanic risk
Ash fall and ash clouds: all locations in path

32. United States Volcanic Hazards

33. 5.4 Effects of Volcanoes 50 to 60 volcanoes erupt each year worldwide
In the United States, 2 to 3 per year, mostly in Alaska
Most eruptions are in sparsely populated regions
500 million people live close to volcanoes
Japan, Mexico, Philippines, and Indonesia and several U.S. cities are vulnerable
Primary Effects
Lava flows, ash fall, pyroclastic flows, lateral blasts, and release of volcanic gases
Secondary Effects
Debris flows, mudflows, landslides or debris avalanches, floods, fires, and tsunamis
Global cooling of the atmosphere in a large eruption

34. Selected Historic Volcanic Events

35. Locations of Volcanoes in the United States

36. Lava Flows One of most familiar products of volcanic activity
Results when magma reaches the surface through crater or from a vent
Three types: basaltic, andesitic, rhyolitic
Basaltic is the most abundant
Can form lava tubes
Can move slowly or more rapidly
Basaltic lavas are the most rapid at 15–35 km/h (10–30 mph)
Pahoehoe lavas are smooth and ropey
AA are blocky flows
Move slow enough for people to get out of the way

37. Lava Flows

38. Lava Tubes

39. Pyroclastic Activity
Explosive volcanism that blasts magma and rocks from a vent
Known as tephra
Fine dust to sand-sized ash (less than 2mm)
Small gravel-sized lapilli (2 to 64 mm)
Large angular blocks and smooth-surfaced bombs (greater than 64mm)
Falls cool and lightly like snow or hat, fast, and heavy like a freight train
Accumulation forms a pyroclastic deposit

40. Pyroclastic Activity

41. Pyroclastic Activity, cont.
Ash Fall
Explosive fragmentation of magma during an eruption
Can cover hundreds or thousands of square kilometers
Direct hazards
Vegetation may be destroyed
Surface water may be contaminated by sediment
Fine particles clog the gills of fish and kill other aquatic life
Ash accumulation on roofs may cause structural damage
Irritation of the respiratory system and eyes
Engines of jet aircraft may “flame out”

42. Volcanic Tephra on Buildings

43. Pyroclastic Activity, cont.
Pyroclastic Flows
One of the most lethal aspects of volcanic eruptions
Hot and race down side of volcano at speeds exceeding 400 km/hr (~250 mph)
Hot expanding gases carry low-density ash upward
Base of flow contains larger debris
Also known as ash flows, hot avalanches, or “glowing clouds”
Catastrophic if populated area in path
Responsible for more deaths than any other hazard
Formation
Large ash-generating eruptions (VEI>3)
Lateral blasts: explosion destroys part of the volcano
Lava dome collapse: most common

44. Pyroclastic Flow

45. Plaster Casts of Volcano Victims

46. Poisonous Gases Emitted gases
Carbon dioxide and water vapor account for 90 percent of emissions
Carbon dioxide gas is odorless and heavy
It can accumulate suffocating people
Sulfur dioxide
Can produce acid rain
Others: carbon monoxide and hydrogen sulfide
Toxic concentrations rarely reach populated areas
Chemicals can contaminate soil and plants
Can cause air pollution known as vog (volcanic smog)

47. Debris Flows, Mudflows, and Volcanic Landslides
Also known as lahars
Loose volcanic ash becomes saturated with water, becomes unstable, and moves down volcano
Can occur in the absence of an eruption
Debris flows
Glaciers and ice are melted by volcano and mix with sediment and rock
Similar to wet concrete

48. Debris Flows, Mudflows, and Volcanic Landslides, cont.
Finer than debris flows
Populous areas of Pacific Northwest are built on old mudflows
Not unlikely for new flows to occur
Landslides
May be triggered outside of an eruption
May affect areas far from their source
Can cause tsunamis

49. Volcanic Mudflow Catastrophe

50. Mount Rainier Volcanic Hazard Map

51. Case Study 5.3 Eyjafjallajokull 2010 Eruption - Applying the 5 Fundamental Concepts
Eruption on May 18, 1980
Exemplifies many types of events expected from a Cascade volcano
Unique and complex eruption
Have learned a great deal from the eruption

52. Mount St. Helens, Before and After

53. Mount St. Helens, Before and After

54. Case Study 5.3 Eyjafjallajokull 2010 Eruption - Applying the 5 Fundamental Concepts, cont.
120 years of dormancy
March 1980 – seismic activity and small explosions
May 1 – bulge begins to grow on northern flank at rate of 1.5 m (5 ft.) per day
May 18, 8:32 A.M. – M 5.1 earthquake triggers landslide/debris avalanche of the bulge area
Seconds later, lateral blast from bulge area at rate of 480 km/hr (300 mph)

55. Case Study 5.3 Eyjafjallajokull 2010 Eruption - Applying the 5 Fundamental Concepts, cont.
One hour after blast, vertical cloud of ash extends to stratosphere
9 hours of ash falls to cover areas of Washington, northern Idaho, western and center Montana
Pyroclastic flows begin at this time down the northern slope
Mudflows begin at speeds of 29 to 55 km/hr (18 to 34 mph)

56. Mount St. Helens Erupts

57. Debris Avalanche and Ash Cloud

58. Barren Landscape Produced by Eruption

59. Case Study 5.3 Eyjafjallajokull 2010 Eruption - Applying the 5 Fundamental Concepts, cont.
Summary
57 people were killed
Flooding destroyed > 100 homes
800 feet of timber flattened
Damage > $1 billion
September 23, 2004, Mount St. Helens reawakens
Lava dome begins to form on crater floor
Continues to form today

60. Continued Growth of Dome in Crater

61. 5.5 Linkages between Volcanoes and Other Natural Hazards
Fire
Hot lava may ignite plants and structures
Earthquakes
Usually accompany or precede volcanic activity
Landslides
Mudflows, ashflows, and landslides are common secondary effects
Climate change
Debris can reflect sunlight causing global cooling

62. 5.6 Natural Service Functions of Volcanoes
Volcanic soils
Good for coffee, maize, pineapples, sugar cane, and grapes
Geothermal power
Can create energy for nearby urban areas
Mineral resources
Gold, silver, etc. and non-metallic rocks
Used for soap, building stone, aggregate for roads, railroads, etc.

63. 5.6 Natural Service Functions of Volcanoes, cont.
Recreation
Health spas and hot springs
Hiking, snow sports, and education
Kilauea National Park
Creation of new land
Hawaiian Islands

64. 5.7 Human Interactions with Volcanoes
Humans do not affect the frequency or severity of eruptions
Minimization of loss of life and property damage is best action

65. 5.8 Minimizing the Volcanic Hazard
Forecasting is major component to reduce volcanic hazards
“Forecast” is a probabilistic statement
Describes time, place, and character
Analogous to forecasting weather
Not as precise as a prediction

66. Forecasting
Unlikely to accurately forecast the majority of volcanic activity in the near future
Need experience with actual eruptions
Better able to predict eruptions in Hawaiian Islands
Forecasting uses information gained by
Monitoring seismic activity
Monitoring thermal, magnetic, and hydrologic conditions
Monitoring the land surface to detect tilting or swelling of the volcano
Monitoring volcanic gas emissions
Studying the geologic history of a particular volcano or volcanic center

67. Forecasting, cont. Seismic activity monitoring
Shallow earthquakes and swarms can precede eruption
May not provide enough time for evacuation
Thermal, magnetic, and hydrologic monitoring
Hot magma changes temperatures, magnetic properties, and groundwater level
Detected by satellite remote-sensing or infrared aerial photography
May also melt snow, showing new “hot” activity
Ground or aerial magnetic surveys show new magnetic properties

68. A Volcano Reawakens

69. Forecasting, cont. Land surface monitoring
Monitoring growth of bulges or domes
Kilauea tilts and swells
Monitoring volcanic gas emissions
Changes in CO2 amounts correlate with volcanic processes
Geologic history
Mapping of volcanic rocks and deposits give idea of types of effects to be expected

70. Inflation and Tilting Before Eruption

71. Volcanic Alert or Warning
USGS alert notification system
Ground-based volcano alert levels
Aviation-based color code levels
Four levels
Normal - Green
Advisory - Yellow
Watch - Orange
Warning - Red
For some eruptions, hazard on the ground or in the air will differ and higher alerts or codes will be issued

72. U.S. Geological Survey Volcanic Alert Levels and Aviation Color Codesa

73. 5.9 Perception of and Adjustment to the Volcanic Hazard
Perception of volcanic hazards
Adjustments to volcanic hazards
Attempts to control lava flows

74. Perception of Volcanic Hazards
Reasons for people to live near a volcanic hazard
Place of birth
Fertile land for farming
People believe eruption is unlikely
Economic limitations
Good education can help people understand volcanic hazard
Volcanic crisis can develop when scientists predict a volcanic hazard for near future
Improved communication among scientists, emergency managers, educators, media, and private citizens is key

75. Adjustments to Volcanic Hazard
Primary adjustment is evacuation
Relocating people out of the hazard area prior to eruption
Also psychological adjustment to losses

76. Attempts to Control Lava Flows
Hydraulic chilling
Water is used to chill and control the lava flow
Used in Iceland
Edges and surface of the flow were cooled with fire hoses
Bulldozers were moved up on the slow flow for a large water pipe
The plastic pipe did not melt as long as water was flowing in it
Small holes allowed the cooling of hot spots along parts of the flow
Wall construction
Walls used to redirect lava flow

77. Fighting Lava Flows

78. Eyjafjallajökull 2010 Eruption – Applying the 5 Fundamental Concepts
Iceland sits atop a hot spot
Volcanic eruption once every three to four years
Fortunately, most Icelandic eruptions are generally effusive and have a VEI of no more than 1
Most volcanoes are localized
Changed with Eyjafjallajökull volcano in 2010
Several signs
Seismic activity became more shallow
Uplift and tilting detected
Rate of deformation was as much as 5 mm per day

79. Icelandic Volcano Monitoring

80. GPS and Seismic Data

81. Eyjafjallajökull 2010 Eruption – Applying the 5 Fundamental Concepts, cont.
Eruption in phases
Effusive, Icelandic-type eruption
Lasted about 3 weeks
Generated a spectacular fire curtain display and lava falls
Explosive eruption
Forced evacuations
Caused flooding
Damage from debris and icebergs
Towering eruption column of ash

82. Geotourists Witness Fissure Eruption

83. Eyjafjallajökull 2010 Eruption – Applying the 5 Fundamental Concepts, cont.
Volcanic ash
Winds blew ash column towards Europe
“No fly zones”
By April 18, most air travel was suspended
Airspace closed for more than a week
Winds spared most of Iceland
Southeastern corner covered by 1-2 inches of ash
Total darkness from April 17 to early April 18
Toxic levels of water-soluble fluoride in ash could harm people and animals
Eruptions not declared over until 6 months later

84. Ash Shuts Down Air Travel in Europe

85. Chapter 5 Summary
Volcanic activity is directly related to plate tectonics. Most volcanoes are located at plate boundaries, where magma is produced in the spreading or sinking of lithospheric plates.
Lava is magma that has been extruded from a volcano.
Magma comes from melting of the asthenosphere.
Features of volcanoes include vents, craters, and calderas.

86. Chapter 5 Summary, cont.
Most explosive volcanic eruptions are from the classic, cone-shaped stratovolcanoes that occur above subduction zones, particularly around the Pacific Rim.
Volcanic domes are smaller then stratovolcanoes but develop similarly above subduction zones and are composed of viscous magma.
The largest volcanoes, shield volcanoes, are common at mid-ocean ridges such as Iceland, and over mid-plate hot spots such as the Hawaiian Islands.

87. Chapter 5 Summary, cont.
Large calderas are created by infrequent, huge, violent eruptions.
Specific geographic regions of North America at risk from volcanoes include the northwestern coast of California; the western coasts of Oregon and Washington and parts of British Columbia and Alaska, Long Valley, and the Yellowstone National Park area.
Primary effects of volcanic activity include lava flows, pyroclastic hazards, and, occasionally, the emission of poisonous gases.

88. Chapter 5 Summary, cont.
Lava flows, which can move as fast as 35 mph, but often move much slower, do not represent a serious hazard for loss of life because they can often be avoided.
Pyroclastic hazards include volcanic ash falls, which may cover large areas with carpets of cool ash that can destroy some structures and ruin agricultural land, but loss of life is less common.
Secondary effects of volcanic activity include debris flows and mudflows, generated when melting snow and ice or precipitation mix with volcanic ash.

89. Chapter 5 Summary, cont.
Volcanoes are linked to other natural hazards such as fire, earthquakes, landslides, and climate change.
Volcanoes provide fertile soils, a source of power, mineral resources, recreational opportunities, as well as newly created land.
Sufficient monitoring of seismic activity; thermal, magnetic, and hydrologic properties; and change in the land surface, combined with knowledge of the recent geologic history of volcanoes, may eventually results in reliable forecasting of volcanic activity.

90. Chapter 5 Summary, cont.
Forecasts of eruptions have been successful, particularly for Hawaiian volcanoes and Mount Pinatubo in the Philippines.
The U.S. Geological Survey has developed an alert notification system for volcanic activity that has four levels for hazards on land and four color codes for aviation hazards.

91. Chapter 5 Summary, cont.
Efforts to meet the goal of reducing volcanic hazards are focusing on human and societal issues of communication; the objective is to prevent a volcanic crises from becoming a disaster or catastrophe.
Perception of the volcanic hazard is apparently a function of a person’s age and length of residency near the hazard. Community-based education plays an important role in informing people about the hazards of volcanoes.