1. Unit 4: Weathering, Erosion, Deposition (WED)
Destructive Forces

2. DESTRUCTIVE FORCES! Plate tectonics builds the earth surface up
But what goes up, must come down!
Once exposed to the air, water or wind, rock will begin its destructive cycle
It will weather down!

3. What is weathering?
The breaking down of rock due to physical and/or chemical changes in the rock as it is exposed to the atmosphere
Occurs at the interface between the atmosphere and the lithosphere
Results in smaller pieces of rock called sediments

4. Physical weathering
Results in a change in appearance of rock (size, shape, state)
Types include: frost action, plant action, pressure unloading

5. Frost action Occurs in a cold and moist climate
Alternating freezing and melting of water in the rock cracks the rock

6. Plant action
Plant roots grow into small cracks in rock and widen them

7. Pressure unloading
Rock cracks when pressure over the rock is removed

8. Chemical Weathering
Results in a change in chemical composition of the rock
Types include: oxidation, acid reactions, and hydrolysis

9. Oxidation
Addition of oxygen to metal…results in rust (iron oxide)

10. Hydrolysis
Chemical weathering by reaction of water with other substances
When certain minerals are exposed to water they dissolve into ions…ex: feldspar
Feldspar will chemically weather into clay (kaolinite)
Water will help any chemical reaction

11. Acids
Gases such as sulfur dioxide, nitrogen dioxide, carbon dioxide will dissolve in rainwater forming acid rain (sulfuric acid, nitric acid, and carbonic acid -a weak acid)
Calcite will dissolve completely in carbonic acid-thus chemically weather any rock containing this mineral easily
Acid rain which forms naturally, for example volcanic activity, or by pollutants, harms any exposed rock, buildings and monuments

13. Caves Form!

14. End RESULT of Weathering:
SEDIMENTS!
INCLUDES-CLAY, SILT, SAND, PEBBLES AND COBBLES
SEE ESRT P6,7

15. What can affect the rate of weathering?
Size of the sediment
Type of mineral (hardness)
Temperature
Humidity (amount of moisture present)

16. How does weathering connect to the rock cycle?

18. Sediments form sedimentary rocks…

19. What is soil? A mixture of weathered rock and organic remains (humus)
Forms at interface between the atmosphere and the lithosphere

20. How does soil form? 1st: rocks weathers
2nd: leaching of minerals adds nutrients to lower layers from top layer
3rd: biological activity such as decomposition add organic matter (humus) to soil, soil is mixed by earthworms
Takes 500 to 1000 years to form

21. Soil Horizons A=topsoil (fertile layer) B=Subsoil C=Parent Rock Types:
Residual or
transported

22. What measure can be done to conserve Soil?
Soil is a natural resource and must be protected!
Several methods exist to protect soil such as contour farming, no-till farming, terracing, and crop rotation
These all prevent erosion of the topsoil by wind or water

23. Why is it important to protect?
We need it to sustain ecosystems
Producers take nutrients from the soil and convert it to food with the help of sunlight
Basis of the food chain