1. Building Earth’s Surface
PowerPoint Lectures to accompany Physical Science, 9e
Chapter 19
Building Earth’s Surface
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Core Concept
The surface of Earth is involved in plate tectonic processes that result in an ongoing building-up of the surface.

3. Interpreting Earth’s Surface
Principle of uniformity
“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, …

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

5. Stress and Strain Stress Strain
Force tending to compress, pull apart or deform a rock
Three stress forces
Compressive stress
Plates moving together
Tensional stress
Plates moving apart
Shear stress
Plates sliding past each other
Strain
Adjustment to stress
Three strain types
Elastic strain
Returns to original shape
Plastic strain
Molded or bent
Do not return to original shape
Fracture strain
Rock cracks or breaks

6. Stress and Deformation
Possible material responses to stress
No change
Elastic change with recovery
Plastic change with no recovery
Breaking from the pressure
Rock variables
Nature of the rock
Temperature of the rock
Speed of stress application
Confining pressure
Interplay produces observed rock structures

7. Folding Sedimentary rocks Folds 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
Anticline: arch-shaped structure
Syncline: trough-shaped

8. Folding Folds Bends in layered bedrock
Result of stress produced plastic strain
Widespread horizontal stress can produce domes and basins
Anticline: arch-shaped structure
Syncline: trough-shaped

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. Classes of Faults 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

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

12. 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

13. Causes of Earthquakes Elastic rebound theory
Two plates press tightly together
Friction restricts motion
Stress builds until friction or rock rupture strength is overcome
Stressed rock snaps suddenly into new position

14. Locating and Measuring Earthquakes
Focus
Actual origin of seismic waves
Epicenter
Location on Earth’s surface directly above the focus
Seismograph
Instrument used to detect and measure earthquakes
Detects three kinds of waves
P-wave (longitudinal)
S-wave (transverse)
Surface wave (up and down)

15. 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

16. Classification of Earthquakes
Based upon depth of focus
Shallow-focus earthquakes
Down to 70 km deep
85% of all earthquakes (surface rocks more brittle; more plate friction near surface)
Intermediate-focus earthquakes
70 to 300 km deep
Upper part of the mantle
Deep-focus earthquakes
350 to 700 km deep
Lower part of upper mantle
About 3% of all earthquakes

17. Measuring Earthquake Strength
Effects: structural damage to buildings, fires, landslides, displacement of land surfaces, tsunami (tidal wave)
Mercalli scale
Relative intensity
I (not felt) to XII (total destruction with visible ground waves)

18. Measuring Earthquake Strength
Richter scale
Based on swings in seismograph recordings
Logarithmic scale
3 (not felt); 9 (largest measured so far)

19. Earthquake Safety During the Shaking Don’t panic
If indoors, stay there. Stay away from glass. Do not use any other flames.
If outside, move away from buildings. Stay in open.
If in car, bring to a stop as soon as possible but stay in car.
After the Shaking
Check but do not turn on utilities.
Turn on radio or TV.
Stay off telephone unless to report emergency.
Stay out of damaged buildings.
Don’t go sightseeing.

20. 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

21. Folded and Faulted Mountains
Domed mountains
Begin as a broad arching fold
Overlying sedimentary rocks weather away, leaving more resistant granite peaks

22. Folded and Faulted Mountains
Fault block mountains
Rise sharply along steeply inclined fault planes
Weathering erodes sharp edges

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

24. Types of Volcanoes Shield volcano Cinder cone volcano
Constructed of solidified lava flows
Broad, gently sloping cones
Cinder cone volcano
Constructed of rock fragments (cinders)
Steeper and smaller than shield volcanoes
Composite volcano
Alternating layers of cinders, ash and lava flows with volcanic mud

25. Other Features Most magma remains underground
Cools and solidifies to form intrusive rocks
Batholith
Large amount of crystalized magma
Stock: small protrusion from a batholith
Batholith intrusions can cause hogbacks
Related processes: dikes, sills, laccoliths,…

26. Overall Picture
Mountain ranges are composites of many different processes, each uniquely structured
Folding
Faulting
Volcanic activity
Especially apparent along converging plate boundaries