1. Chapter 14 Weathering and Erosion

2. Weathering Processes
Weathering - the natural process by which atmospheric and environmental agents, such as wind, rain, and temperature changes, disintegrate and decompose rock at or near the surface.
There are two main types of weathering processes—mechanical weathering and chemical weathering.
Each type of weathering has different effects on rock.

3. Mechanical Weathering
Mechanical weathering is strictly a physical process and does not change the composition of the rock.
Common agents of mechanical weathering are ice, plants and animals, gravity, running water, and wind.
Physical changes within the rock itself affect mechanical weathering.

4. Ice Wedging

5. Heat causes expansion; cooling causes contraction.
Thermal expansion
Repeated daily heating and cooling of rock;
Heat causes expansion; cooling causes contraction.
Expanding and contracting causes cracks.

6. Abrasion
Is the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles
Abrasion is caused by gravity, running water, and wind.

7. Organic Wedging Plants and animals
Root wedging widens fractures in rock.

8. Organic Activity Digging and burrowing activities.
Earthworms and other animals that move soil expose new rock surfaces to both mechanical and chemical weathering.

9. Chemical Weathering Chemical alteration of minerals.
Chemical reactions commonly occur between rock, water, carbon dioxide, oxygen, and acids.
Most effective in a warm, humid climate.
Chemical weathering changes both the composition and physical appearance of the rock.

10. CHEMICAL WEATHERING OXIDATION
ROCKS / MINERALS CHEMICALLY REACT WITH THE OXYGEN IN THE ATMOSPHERE, CAUSING A DECOMPOSITION ON THE MATERIALS

11. CHEMICAL WEATHERING
Dissolution - mineral completely dissolves, leaving only ions in solution.

12. Section 2 Rates of Weathering Factors influencing Weathering Rates
The processes of mechanical and chemical weathering generally work very slowly.
Rock Structures – chemical/mineral composition, Physical features
Topography
Climate

13. Spheroidal Weathering

14. Spheroidal Weathering

16. Differential Weathering
Rocks weather at different rates.
Softer rocks are less resistant to weathering.

17. Section 3 Soil Characteristics of Soil
The characteristics of soil depend mainly on the rock from which the soil was weathered, which is called the soil’s parent rock.

18. Soil Composition
Soil composition refers to the materials of which it is made.
The color of soil is related to the composition of the soil.
Soil moisture can also affect color.

19. Soil Horizons
Horizon O
Bedrock

20. SOIL HORIZONS
O-HORIZON
A-HORIZON
B-HORIZON

21. O horizon Organic rich, humus
Organic mineral matter
Organic rich, humus
Decaying organic matter releases nutrients

22. A horizon Organic rich, often dark in color
Zone of leaching (lots of chemical weathering)
Organic rich, often dark in color
Decaying organic matter releases nutrients

23. B horizon High clay content, reddish color from iron.
Zone of accumulation – minerals (clay and iron oxide) are washed down from above.
High clay content, reddish color from iron.
Able to retain moisture because of clay content

24. C horizon Parent material – grading from weathered to unweathered.
Parent material can be:
Bedrock
Stream sediments
Volcanic ash

25. Controls of Soil Formation
Parent Material
Time
Climate
Plants and Animals
Slope

26. Soil and Climate
Climate is one of the most important factors that influences soil formation.
Climate determines the weathering processes that occur in a region.
These weathering processes, in turn, help determine the composition of soil.

27. Soil and Topography
Because rainwater runs down slopes, much of the topsoil of the slope washes away.
Therefore, the soil at the top and bottom of a slope tends to be thicker than the soil on the slope.
Topsoil that remains on a slope is often too thin to support dense plant growth.

28. Section 4 Erosion
erosion a process in which the materials of Earth’s surface are loosened, dissolved, or worn away and transported from one place to another by a natural agent, such as wind, water, ice, or gravity
When rock weathers, the resulting rock particles do not always stay near the parent rock.
Various forces may move weathered fragments of rock away from where the weathering occurred.

29. Soil Erosion
Ordinarily, new soil forms about as fast as existing soil erodes.
Some farming and ranching practices increase soil erosion.
Soil erosion is considered by some scientists to be the greatest environmental problem that faces the world today.

30. Soil Conservation
Certain farming techniques can increase the rate of erosion.
Land clearing accelerates topsoil erosions.
Soil erosion can be prevented by soil conservation methods

31. Soil Conservation Methods
Contour Plowing
Strip-Cropping
Terracing
Crop Rotation

32. End of Chapter 14