1. Chapter 7: Weathering, Erosion, and Soil

2. relate to weathering and
How does this cartoon
relate to weathering and
erosion?

3. BIG Idea:
Weathering and erosion are agents of change on Earth’s surface.

4. Weathering: the process by which rocks are broken down chemically and physically by the action of water, air, and organisms.

5. I. WEATHERING PROCESSES
Mechanical Weathering
Strictly a physical process
Rocks and minerals break into smaller pieces
No change to chemical composition

6. Agents of MECHANICAL Weathering:
ice
plants and animals
gravity
running water
wind

7. 1. Ice (Frost) Wedging
water seeps into rock cracks and then freezes

8. What causes this to happen?

10. 2. Pressure
Exfoliation: outer rock layers are stripped away (like an onion’s layers can be peeled)

12. 3. Organic Activity

13. Root Action: tree roots grow within cracks in rocks and cause the rocks to split

14. 4. Abrasion
The collision of rocks with one another, causing them to break down
Agents of abrasion:
gravity
running water
wind

15. wearing down or smoothing
of a
material due to
constant collisions

16. Wind Abrasion

17. Water Abrasion

18. B. Chemical Weathering
Process by which rocks and minerals undergo changes in their composition
Can cause some substances to dissolve
Some new minerals form
New minerals have properties different than those of original rock

20. What items have you seen rusted?
What could you do to such objects to prevent or reduce rusting?

21. Agents of CHEMICAL Weathering:
Water
Oxygen
Carbon dioxide
Acid precipitation

22. Hydrolysis: reacting with water
Carbonation: carbon dioxide combines with water to produce carbonic acid (dissolves limestone)
Oxidation: reacting with oxygen (rust)

23. Carbonic acid creates caves

24. Oxidation of the iron in the rock causes a red hue

25. Acid precipitation (rain): sulfur dioxide, carbon dioxide and nitrogen oxides released into atmosphere by human activities; gases combine with oxygen and water to form strong acid rains
Plant acids: from decaying plants

27. II. RATES OF WEATHERING
All rocks do not weather at the same rate (speed)…
Some factors that affect the rate at which rocks weather are:

28. A. Rock Composition
Igneous and metamorphic rocks break down more SLOWLY
Hardest minerals resist weathering (i.e. quartz)
Rocks containing calcite weather QUICKLY

29. Which layer is MORE resistant to weathering? LEAST resistant?D C B

32. B. Amount of Exposure
time exposed
surface area

33. Surface Area
Which will weather faster, solid rock or crushed rock?

34. The crushed rock of course!
the large rock is tightly packed and has less surface area exposed
the crushed rock is loosely packed and has more surface area exposed

35. Increased surface area = increased weathering

37. C. Climate
Rocks in tropical regions weather faster than rocks in dry desert areas
More rain, humidity, wind, and temperature range = faster weathering

38. Physical Weathering:
works better in a cool and dry climate
Chemical Weathering:
works better in a hot and moist environment
(more water = more weathering)

39. Cleopatra’s Needle stood in Egypt (hot/dry) for 3,000 years…

40. It was only in New York City for 100 years
Rain, ice, and pollution destroyed it

41. Compare the two tombstones in the next picture…
How do they compare in appearance?
Which appears more weathered?

42. marble
slate

43. Which tombstone is older?
marble
slate

44. This means that rocks can weather at different rates!
marble
slate

45. D. Topography
Higher elevation = faster weathering (colder, more ice wedging)
Steep slopes - gravity pulls rocks down hill

46. III. Weathering and Soil
Soil: loose rock fragments and clay from weathered rock mixed with organic material.

47. A. Soil Composition A = Humus - dark organic material
B & C = Soil – mixture of minerals, gases, and dead organisms
D = Regolith – layer of weathered rock fragments
E = Bedrock – solid unweathered rock

48. B. Soil Profile Soil Profile: cross section of the soil layers
Horizons: layers in the soil

50. Two Types of Soil: Residual: parent material is the local bedrock
Transported: develops from parent material that has been moved far from original location

51. Residual Soils
forms from the weathering of the underlying bedrock

52. Transported Soils Due to…

53. IV. EROSION
Process by which the products of weathering are TRANSPORTED (moved)
Agents of erosion:
Running WATER
wind
glaciers (ice)

54. A. Gravity and Erosion
Talus: rock
fragments at the
base of a slope

55. Mass Movements
Rock fall: fall of rocks from a steep cliff

57. Landslide: loose soil and rocks that move down the slope of a hill

60. Mudflow: rapid movement of a large mass of mud

61. Creep: slow downhill movement of rocks and soil

62. B. Landforms and Erosion
3 major landforms:
Mountains: steep, high elevations
Plains: flat or gently sloped, not high above sea level
Plateaus: high elevations, flat surfaces