Unit 2 - Earthquakes and Volcanoes (2017/2018)

1. Earthquakes and
Volcanoes
Unit 2

2. 12.1 How and Where
Earthquakes Happen
•Earthquakes – movements of the ground
that are caused by a sudden release of
energy when rocks along a fault move.

3. 12.1 How and Where
Earthquakes Happen
•Why Earthquakes Happen
1. Rocks on both sides of a fault become
locked due to friction.

4. 12.1 How and Where
Earthquakes Happen
•Why Earthquakes Happen
2. Stress builds up and the crust deforms.

5. 12.1 How and Where
Earthquakes Happen
•Why Earthquakes Happen
3. Rock fractures and snaps back to its
original shape, releasing stored energy.

6. 12.1 How and Where
Earthquakes Happen
•Elastic Rebound – when deformed
(stretched/bent/squeezed) rock releases
energy and returns to its original shape.

7. 12.1 How and Where
Earthquakes Happen

8. 12.1 How and Where
Earthquakes Happen

9. 12.1 How and Where
Earthquakes Happen

10. 12.1 How and Where
Earthquakes Happen
•Anatomy of an Earthquake
• Focus – the location within Earth along a fault
at which the first motion of an earthquake
occurs.

11. 12.1 How and Where
Earthquakes Happen
•Anatomy of an Earthquake
• Epicenter – the point on Earth's surface
directly above an earthquake's Focus.

12. 12.1 How and Where
Earthquakes Happen
•Seismic Waves
• Body Waves
• Surface Waves

13. 12.1 How and Where
Earthquakes Happen
•Body Waves – waves that move through
the body of a medium.
• P Waves
• S Waves

14. 12.1 How and Where
Earthquakes Happen
•Primary Waves (P Waves) – move rock
back and forth parallel to the direction of
the wave.
• The fastest moving wave and the first to be picked
up by a seismograph.
• Compression Waves, Left to Right

15. 12.1 How and Where
Earthquakes Happen

16. 12.1 How and Where
Earthquakes Happen

17. 12.1 How and Where
Earthquakes Happen
•Secondary Waves (S Waves) – move rock
side to side perpendicular to the direction
of the wave.
• The second wave to be picked up by a
seismograph.
• Only travel through solids.
• Shear Waves, Up and Down

18. 12.1 How and Where
Earthquakes Happen

19. 12.1 How and Where
Earthquakes Happen

20. 12.1 How and Where
Earthquakes Happen
•Surface Waves – wave that travels along
the surface.
• Love Waves
• Rayleigh Waves

21. 12.1 How and Where
Earthquakes Happen
•Surface Waves
•Love Waves – move rock side to side
perpendicular to the direction of the wave.

22. 12.1 How and Where
Earthquakes Happen
•Surface Waves
•Rayleigh Waves – rock moves in an
elliptical, rolling motion.

23. 12.1 How and Where
Earthquakes Happen
•Shadow Zone – an area on Earth’s surface
where no direct seismic waves from a
particular earthquake can be detected.

24. 12.1 How and Where
Earthquakes Happen

25. 12.1 How and Where
Earthquakes Happen

26. 12.1 How and Where
Earthquakes Happen

27. 12.1 How and Where
Earthquakes Happen

28. 12.1 How and Where
Earthquakes Happen

29. 12.1 How and Where
Earthquakes Happen

30. 12.1 How and Where
Earthquakes Happen

31. 12.1 How and Where
Earthquakes Happen
•Fault Zones – a region of numerous,
closely spaced faults.
• Ancient deep/buried fault zones left from
Pangaea shift and cause minor earthquakes
away from boundaries.

32. 12.2 Studying Earthquakes
•Seismology – the study of
earthquakes and seismic waves.

33. 12.2 Studying Earthquakes
•Seismograph – an instrument that
records vibrations.
• The Machine

34. 12.2 Studying Earthquakes
•Seismogram – a tracing of earthquake
motion that is recorded by a
seismograph.
• The Data

35. 12.2 Studying Earthquakes
•Locating an Earthquake
• Scientists use the arrival times of the P
waves and S waves to determine the
epicenter of an earthquake.
• Because the P waves travel faster than S
waves, there is lag time between the wave.
• Seismic data from three seismic stations is
needed to determine the epicenter.

36. 12.2 Studying Earthquakes

37. 12.2 Studying Earthquakes

38. 12.2 Studying Earthquakes

39. 12.2 Studying Earthquakes
•Magnitude – a measure of the strength
of an earthquake.
• Does not depend on location from the
earthquake epicenter.
• Richter Scale
• Measure ground motion (shaking).
• *Outdated*
• Moment of Magnitude
• Measures total energy released.
• *Scale used today*

40. 12.2 Studying Earthquakes

41. 12.2 Studying Earthquakes
•Intensity – the amount of damage
caused by an earthquake.
•Depends on the location from the
earthquake epicenter.
•Modified Mercalli Scale

42. 12.2 Studying Earthquakes

43. 12.3 Earthquakes and Society
•Tsunami – a giant ocean wave that
forms after an earthquake.

44. 12.3 Earthquakes and Society
• Earthquake Safety
• Before
• Be prepared by having supplies.
• Canned food, bottled water, flashlights, batteries,
portable radio.
• Emergency Plans
• Know where to go.
• Know how to turn off gas, electricity, and water lines.

45. 12.3 Earthquakes and Society
•Earthquake Safety
•During
• STAY CALM!
• Stand in doorways.
• Stay away from windows and heavy
furniture.

46. 12.3 Earthquakes and Society
•Earthquake Safety
•After
• Be cautious.
• Check for fire and other hazards.
• Wear shoes.
• Stay away from downed power lines.

47. 12.3 Earthquakes and Society
•Earthquake Warnings
and Forecasts
• There is currently no
reliable way to
determine when and
where an earthquake
will occur.
• Scientists study past
earthquakes to make
prediction forecasts of
future earthquakes.

48. 12.3 Earthquakes and Society
•Earthquake Warnings and Forecasts
•Seismic Gap – an area along a fault
where relatively few earthquakes have
occurred recently, but where strong
earthquakes have occurred in the past.
Earthquake data is plotted on a
map and areas, on active faults,
that have not had much recent
seismic activity are in what
scientists call seismic gaps.
Scientists believe these areas will
soon experience an earthquake.

49. 12.3 Earthquakes and Society

50. 12.3 Earthquakes and Society
•Foreshock – a small earthquake that
often comes before a major
earthquake.

51. 12.3 Earthquakes and Society
•Aftershock – a small earthquake that
follows the main earthquake.

52. 13.1 Volcanoes and Plate Tectonics
•Volcanoes – a vent or fissure in Earth‘s
surface through which magma and gases
are expelled.

53. 13.1 Volcanoes and Plate Tectonics
• Active = erupted within the last 10,000 years.
• Erupting = active volcano that is currently erupting.
• Dormant = active that is not erupting, but is supposed to
erupt again.
• Extinct = has not had an eruption in the last 10,000 years
and is not expected to erupt again in the near future.

54. 13.1 Volcanoes and Plate Tectonics
•Magma – molten (melted) rock beneath
Earth’s surface.
• Melted crust and mantle.

55. 13.1 Volcanoes and Plate Tectonics
•Volcananism – any activity that includes
the movement of magma toward or onto
Earth’s surface.

56. 13.1 Volcanoes and Plate Tectonics
•Lava – molten (melted) rock on Earth’s
surface.

57. 13.1 Volcanoes and Plate Tectonics
•Locations of Volcanoes
• Subduction Zones
• Ocean Ridges
• Hot Spots

58. 13.1 Volcanoes and Plate Tectonics
•Subduction Zones – a destructive plate
boundary where oceanic crust is being
pushed down into the mantle beneath a
second plate.
• The plate that is more dense sinks.
• Oceanic plates are more dense than
continental plates.

59. 13.1 Volcanoes and Plate Tectonics

60. 13.1 Volcanoes and Plate Tectonics
•Mid-Ocean Ridge – an underwater
mountain range created at a divergent
boundary.
• Divergent Plate Boundary
• Mid-Atlantic Ridge

61. 13.1 Volcanoes and Plate Tectonics
•Hot Spot – volcanically active areas that
lie far away from plate boundaries.
• Plate moves over a magma/magma plume.
• Young Volcanos = Close to Hotspot
• Old Volcanos = Far from Hotspot
• Hawaii and Yellowstone

62. 13.2 Volcanic Eruptions
•Viscosity – a measure of a
fluid’s resistance to flow.
• High Viscosity = Slow Flow
• When lava cools down it
flows slower.
• Low Viscosity = Fast Flow
• When lava heats up it flows
quicker.

63. 13.2 Volcanic Eruptions
•Types of Magma
• Mafic (thin)
• Felsic (thick)

64. 13.2 Volcanic Eruptions
•Mafic – thin magma/lava that cools into
dark rock high in magnesium and iron that
forms ocean crust.

65. 13.2 Volcanic Eruptions
•Felsic – thick magma/lava that cools into
light rock high in silicate minerals that
forms ocean and continental crust.

66. 13.2 Volcanic Eruptions
•Types of Eruptions
• Quiet Eruptions
• Lava Flows
• Explosive Eruptions.

67. 13.2 Volcanic Eruptions
•Quiet Eruptions
• Mafic (thin) lava erupts easily and quietly
through cracks.

68. 13.2 Volcanic Eruptions
•Lava Flows
• Mafic (thin) lava cools rapidly forming a crust
on the surface.
• Lave continues to flow below.

69. 13.2 Volcanic Eruptions
•Pahoehoe – smooth ropey texture.

70. 13.2 Volcanic Eruptions
•Aa – crust deforms rapidly breaking into
jagged chunks.

71. 13.2 Volcanic Eruptions
•Blocky – forms from thicker mafic lava
when crust breaks into large chunks.

72. 13.2 Volcanic Eruptions
•Explosive Eruptions
• Thicker, sticky felsic lava plugs up vents and
builds up pressure before exploding.
• The more trapped gases the greater the
explosive force.

73. 13.2 Volcanic Eruptions
• Pyroclastic Material – fragments of rock that
form during a volcanic eruption.
1. Volcanic Ash = Less than 2mm in diameter
2. Volcanic Dust = Less than .25mm in diameter
3. Lapilli = Less than 64mm in diameter
4. Volcanic Bombs = Large clots of red hot lava
thrown into air
5. Volcanic Blocks = Solid rock blasted into air

74. 13.2 Volcanic Eruptions
•Types of Volcanoes
• Shield
• Composite Cone
• Cinder Cone

75. 13.2 Volcanic Eruptions
•Shield – broad base with gently sloping
sides.
• Forms from quiet eruptions.
• Most shield volcanoes have grown up from
the deep-ocean floor to form islands.
• Largest volcanoes.
• Examples: Mauna Loa in Hawaii.

76. 13.2 Volcanic Eruptions

77. 13.2 Volcanic Eruptions
•Composite Cone – wide base that starts
out gently sloping but then gets steep
near cone.
• Forms from alternating quiet and explosive
eruptions.
• Most explosive and dangerous eruptions.
• Example: Mt. St. Helens in Washington.

78. 13.2 Volcanic Eruptions
Mt. St. Helens in Washington before and after 1980 eruption.

79. 13.2 Volcanic Eruptions
•Cinder Cone – very steep slopes to central
cone.
• Forms from explosive eruptions.
• Smallest volcanoes.
• Example: Sunset Crater in Arizona.

80. 13.2 Volcanic Eruptions

81. 13.2 Volcanic Eruptions

82. 13.2 Volcanic Eruptions

83. 13.2 Volcanic Eruptions
•Calderas – a large, circular depression that
forms when the magma chambers below
a volcano partially empties and causes the
ground above to sink.

84. 13.2 Volcanic Eruptions

85. 13.2 Volcanic Eruptions
•Predicting eruptions is tough, but we use
the following to try:
1) Earthquake activity
2) Temperature changes
3) Bulges
4) Knowledge of previous eruptions