1. TOPIC IX: WEATHERING AND EROSION
Questions:
What is meant by weathering?
How does weathering happen?
What areas tend to have more weather occurring in the United States?

2. Weathering- Breakdown of rocks into particles called Sediment
Weathering occurs when rocks are exposed to:
1. Atmosphere 2. Hydrosphere 3. Living things

3. TYPES OF WEATHERING
1. Physical - Breakdown of rock into smaller pieces without chemical change.
EXAMPLES:
a) Root Action: Plant roots grow through cracks and break the rock.

4. b) Frost Action water freezes and expands in cracks
b) Frost Action water freezes and expands in cracks. As this happens over and over again the rock breaks.
c) Exfoliation: Changes in temperature cause the rock to expand and contract.

5. d) Abrasion: When rocks or sediments rub against another rock
ex: sandblasting

6. 2. Chemical - Breakdown of rock by chemical action that results in a change in mineral composition
EXAMPLES:
a) Oxidation - When elements in the rock react with O2 (oxygen)
Fe (iron) + O2 (oxygen) = | Fe2O2 (iron oxide or rust)

7. b) HYDRATION- When elements in
the rock react with H2O (water- the “universal dissolver”)
Feldspar (common mineral) H2O = Clay
Clay = fine particles that are usually wet

8. c) CARBONATION- When elements are dissolved by acid rain.
Carbon Dioxide + Water = Carbonic Acid or
Sulfur Dioxide + Water = Sulfuric acid
Example: Marble grave stone dissolved by acid rain

9. FACTORS AFFECTING THE RATE AND TYPE OF WEATHERING
1. EXPOSURE- more exposure to air, water and living things the faster the weathering
Therefore, rocks near the surface are weathered and rocks deep under ground are not
DEPTH
WEATHERING
RATE OF

10. 2. PARTICLE SIZE- The smaller the particle size, the greater the total surface area that is exposed to weathering.
SAME OVER ALL VOLUME
MORE EXPOSED AREA
PARTICLE SIZE
WEATHERING
RATE OF

11. EXAMPLES: Quartz is hard, takes a long time to weather.
3. Mineral Composition - Different minerals have different resistances to weathering.
EXAMPLES: Quartz is hard, takes a long time to weather.
Talc is soft, takes a short time to weather.
MINERAL
HARDNESS
WEATHERING
RATE OF

12. 4. Climate - In warm, moist climates chemical weathering is dominant.
Cold climates frost action most effective form of weathering.
A lot of freezing and thawing - frost action is the most effective form of weathering
In dry climates very little weathering happens.
TEMPERATURE
WEATHERING
PHYSICAL
RATE OF
TEMP.
AND MOISTURE
WEATHERING
CHEMICAL
RATE OF

13. PRODUCTS OF WEATHERING
Weathering results in four types of sediment:
1. Solid sediment - sand and pebbles.
2. Colloids clay sized particles (small sediment)
3. Ions - Particles dissolved in water (salty oceans)
4. Soil - a mixture of sediment and organic matter