1. Weathering

3. Physical weathering:
Process by which rocks and minerals break down into smaller pieces
Temperature (freeze/thaw)
Pressure

4. chemical weathering:
Process by which rocks and minerals break down as a result of a chemical reaction

5. chemical weathering:
Water – the reaction of water with other substances is known as hydrolysis (decomposition of minerals)

6. chemical weathering:
Oxygen – chemical reaction where oxygen combines with other substances is called oxidation (ex. Iron)

7. chemical weathering:
Carbon dioxide – when CO2 combines with water in the atmosphere, it forms a weak carbonic acid
Forms clay minerals

8. chemical weathering:
Acid rain – caused by oxidation of sulfur dioxide and nitrogen oxides that are released into the atmosphere by human activities

9. The rate of weathering is affected by:
1. Climate – rain, temperature and evaporation
Chemical weathering = warm temps, abundant rainfall, lush vegetation
Physical (mechanical) weathering = cooler, dryer climates

10. The rate of weathering is affected by:
2.Rock Type – resistance to being broken down. Some rocks are stronger than others

11. The rate of weathering is affected by:
3. Topography – slopes vs. level areas (gravity)

12. Soil Properties
Soil is made of a mixture of weathered rock particles and organic material.
Humus: plant or animal material; dark colored.
Most organic matter in soil comes from plants!

13. Soil is mostly sand, clay or silt particles

14. Soil texture is determined by particle size

15. Soil texture is determined by particle size
Clay: smallest particle size (less than .002 mm);
Sticky, moldable
Least permeable, low porosity
Susceptible to runoff

16. Soil texture is determined by particle size
Silt: Medium particle size (.002 mm mm);’
Crumbly
Less permeable, medium porosity
often found around river banks, river beds or lake beds.

17. Soil texture is determined by particle size
Sand: largest particle size (.06 mm – 2 mm);
Loose, gritty
Very permeable, high porosity
weathered from rocks containing quartz.

18. Soil texture triangle
A soil triangle is used to determine the texture of a sample of soil

19. What is the name of soil that is: - 30 % Clay 50 % Silt 20% Sand

20. Soil Profile
Cross section in which layers (a.k.a. horizons) of soil and bedrock can be seen

21. Soil Horizons O horizon: organic material
A horizon: consists of topsoil (mostly sand and some clay)
B horizon: subsoil reddish brown in color; made mostly of clay; rich in minerals and nutrients
C horizon: deepest layer; consists of broken and solid, unweathered bedrock. (parent material)

23. Soil fertility
Soil fertility is a measure of how well a soil can support the growth of plants

24. Soil fertility Factors that affect soil fertility:
Minerals and nutrients present
Microorganisms present
Amount of precipitation
Topography*
Level of acidity

25. Soil fertility Topography
The topography of a region affects the thickness of the soil
Soil on slopes = more erosion, thinner soil
South-facing slopes = more sunlight, more vegetation