2. Chapters 7 and 8 Slide Lake

3. 15.02.b1 Weathering – the breakdown of rock at or near the earth’s surface

4. Types of Weathering Physical – Mechanical weathering Chemical – Chemical weathering

5. A full, solid block has the least surface area. The interior is safe from exposure. A smashed piece has greatest surface area exposed. The interior can now be attacked.

6. Mechanical Weathering AKA: physical weathering  Breaks a rock into smaller and smaller pieces  Only size changes occur in this process  No chemical composition change occurs in mechanical weathering  Same chemical composition as the parent rock  Results in increased surface area

7. Types of Mechanical Weathering Frost Wedging Root Wedging Pressure Release Let’s look at each one

8. -Repeated freezing and thawing of H 2 O in rocks -Can form potholes in cold climate areas -Ice expands by over 9% in volume as it freezes - Ice at -30 o C is harder than granite Frost wedging

9. Root Wedging Plant action- 1.Tiny root hairs seek out small cracks and pits in rock. 2.Once the root hairs find a place they grow and expand. 3.The expansion causes great pressure and cracks the rock.

10. Pressure Release 1.Rocks formed deep in the Earth are made under high pressure. 2.When the pressure is released the rocks expand & crack. 3.May also be caused by alternate heating and cooling of rocks by weather conditions.

11. Chemical Weathering The breakdown of rocks by chemical means Depends on the stability of minerals More Stable Less Stable Form at low Temps. Form at high Temps. Quartz, K-Feldspar Olivine

12. Two Agents of Chemical Weathering Oxygen causes oxidization (Rust) Carbon dioxide forms a weak acid (carbonic acid), which helps dissolve rock material. Chemical Weathering of Statues, Bath, UK

13. The Result of Chemical Weathering New minerals are formed Dissolved particles are released The amount of chemical weathering is determined by the composition of the Parent rock Temperature increases increase chemical reactions

14. How Granite Weathers Chemical weathering – the alteration of the internal structure of minerals by chemical reactions K Feldspar + carbonic acid + H 2 O  Clay mineral + K bicarbonate + Silica

15. Rates of Weathering Granite versus Marble Factors influencing weathering: -Mineral makeup -Climate

16. Differential Weathering Rocks weather at different rates because of different mineral makeup and exposure to the elements. More resistant rock protrudes as ridges and pinnacles. Bryce National Park, Utah

17. Where is the rock more resistant to weathering?

18. Where is the rock least resistant to weathering?