1. Chapter 16 Earth’s Surface
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2. Interpreting Earth’s surface
Principle of uniformity (James Hutton)
“The present is the key to the past.”
Rocks are changed today by the same processes that changed them in the past
Replaced catastrophic models of previous thinkers
Catastrophic events contribute nonetheless
Volcanoes, earthquakes, meteorite impacts, …

3. Diastrophism
Any process of deformation that changes the Earth’s surface
Produces structures such as plateaus, mountains and folds in the crust
Related to volcanism (the movement of magma) and earthquakes
Basic working theory is plate tectonics

4. Stress and deformation
Possible material responses to stress
No change
Elastic change with recovery
Plastic change with no recovery
Breaking from the pressure

5. Stress and deformation Cont.
Rock variables
Nature of the rock
Temperature of the rock
Speed of stress application
Confining pressure
Interplay between these variables produces observed rock structures

6. Folding Sedimentary rocks Originate from flat sediment deposits
Layers usually horizontal
Folds
Bends in layered bedrock
Result of stress produced plastic strain
Widespread horizontal stress can produce domes and basins

7. Domes

8. Basins

9. Faulting
Fault
Produced by relative movement on opposite sides of a crack
Footwall: mass of rock below the fault
Hanging wall: mass of rock above the fault
Fault plane: surface between the footwall and hanging wall

10. Faulting Cont.
Shows how the hanging wall has moved relative to the footwall.
Hanging wall is on the left
Footwall to the right

11. Three Classes of Faults
1. Normal fault
Hanging wall has moved down relative to the footwall
Related features
Graben
Block surrounded by normal faults drops down
Horst
Block surrounded by normal faults is uplifted

12. Other Faults 2. Reverse fault 3. Thrust fault
Hanging wall moved upward relative to footwall
Result of horizontal compressive stress
3. Thrust fault
Reverse fault with a low-angle fault plane
Faults provide information on the stresses producing the formation

13. Earthquakes Quaking, shaking, vibrating or upheaval of the ground
Result from sudden release of energy from stress on rocks
Vibrations are seismic waves
Most occur along fault planes when one side is displaced with respect to the other

14. Causes of earthquakes Elastic rebound theory
Two plates press tightly together
Friction restricts motion

15. Causes of earthquakes Cont.
Stress builds until friction or rock rupture strength is overcome
Stressed rock snaps suddenly into new position

16. Locating and measuring earthquakes
Focus
Actual origin of seismic waves
Epicenter
Location on Earth’s surface directly above the focus
Locating and measuring earthquakes

17. Locating and measuring earthquakes
Seismometer
Instrument used to detect and measure earthquakes
Detects three kinds of waves
P-wave (longitudinal)
S-wave (transverse)
Surface wave (up and down)

18. Seismic data P-waves travel faster than S-waves
Difference in arrival times correlates to distance from earthquake
Triangulation used to pinpoint epicenter and focus

19. Earthquake Magnitude
Effects: structural damage to buildings, fires, landslides, displacement of land surfaces, tsunami (tidal wave)
Richter scale
Based on swings in seismograph recordings
Logarithmic scale
Number increases with magnitude of the quake
3(not felt); 9(largest)

21. Anchorage, March 1964 (9.2)

22. Northridge, January 1994 (6.7)

23. Oakland, October 1989 (6.9)

25. Tsunomi Very large ocean waves
Generated by strong disturbance in ocean floor
Earthquake, landslide, volcanic explosion
Speeds of up to 725 km/h (459 mi/h)
Wave height can be over 8 m (25 ft)
Very long wavelength of up to 200 km (120 mi)

26. Indian Ocean Tsunami

27. Before and After

28. Before and After

29. WARNING: GRAPHIC PICTURE

30. After Tsunami

31. Origin of mountains Mountains
Elevated parts of Earth’s crust rising abruptly above the surrounding surface
Created by folding and faulting of crust
Three basic origins
Folding
Faulting
Volcanic activity

32. Folded and faulted mountains
Domed mountains
Broad arching fold
Overlying sedimentary rocks weather away, leaving more resistant granite peaks

33. Folded and faulted mountains Cont.
Fault block mountains
Rise sharply along steeply inclined fault planes
Weathering erodes sharp edges

34. Volcanic mountains Volcano
A hill or mountain formed by the extrusions of lava or rock fragments from magma below
Structure: vent, crater, lava flow

36. Mt. St. Helens

37. May 18, 1980

38. Eruption!

39. Ash Clouds

40. Before and After

41. Before and After

42. Spirit Lake Before

43. Spirit Lake After

44. Spirit Lake – 2006

45. Mt Adams from Mt. St Helens showing tree damage

46. Edge of Blast

47. Growing Lava Dome

48. Growing Lava Dome

49. Hot Spots Thermal blooms Maybe up to 2000 miles deep
Plate moves over hot spot
Islands develop over time---depends how long in one area

50. Volcanic Hot Spots

52. Shield Volcano

54. Processes That Tear Down
Slow changes resulting in the breakup, crumbling and other destruction of solid rock
Includes physical, chemical and biological processes
Contributes to
The rock cycle
Formation of soils
Movement of rock materials over Earth’s surface

55. Mechanical weathering
Erosion:
The process of physically removing weathered materials
The physical breakup of rocks without chemical change
Disintegration processes
Wedging
By frost
By trees

56. Chemical weathering Decomposition of minerals by chemical reactions
Oxidation
Reactions with oxygen
Produces red iron oxides

57. Chemical weathering Cont.
2. Carbonation
Reactions with carbonic acid (carbon dioxide dissolved in water)
Easily dissolves limestone
3. Hydration
Reactions with water
Includes dissolving in water and combining with water

60. Erosion Mass movement Erosion caused directly by gravity Creep
The slow movement of soil down a steep slope
Landslide
Any slow to rapid downhill movement of materials

62. Running water Streambed transport: Dissolved materials
Suspended materials
Rolling, bouncing and sliding along stream bed
Streambed evolves over time

63. Streams Youth Landmass recently uplifted
Steep gradient, V-shaped valley w/o floodplain
Boulders, rapids and waterfalls
Maturity
Stream gradient smoothed and lowered
Meanders over floodplain
Old age
Very low gradient
Broad, gently sloping valleys
Sluggish flow; more floods

68. Stream development Cont.
Three stages in the aging and development of a stream
(A) Youth
(B) maturity
(C) old age

69. Deltas Deposits of sediment at the mouth of a river or stream
Stream flow dissipates into an ocean or lake
Erosive and sediment-carrying abilities lost

70. Glaciers Masses of ice on land that move under their own weight
Form from snow accumulated over a number of years

71. Glaciers Cont. Alpine glaciers Form at high elevations
Flow through valleys
Also “valley glaciers”
Continental glaciers
Cover large area of a continent
Today in Greenland and Antarctica

73. Tracy Arm, Alaska

76. Glacier erosion Glaciers: Three mechanisms: Bulldozing
Forms deposits called moraines
Abrasion
Produces powdery, silt-sized rock flour
Plucking
Glacier water freezes into surrounding rock and pulls it along

77. Wind Considerably less efficient than water or ice Two major processes
Abrasion
Natural sandblasting
Produces ventifacts
Shape can depend on prevailing winds
Deflation
Loose material picked up and carried away by the wind

78. Wind Cont. Wind-blown deposits
Dunes: low mound or ridge of sand or other sediment
Loess: fine dust deposited over a large area

79. Death Valley

80. Indiana Dunes

81. Great Sand Dunes

82. Loess Hills Scenic Byway

83. Loess Hills