1. Weathering
The Breakdown of Rocks

2. What is Weathering?
The physical breakdown (disintegration) and chemical alteration (decomposition) of rocks
Yellowstone, 2004
2 types
Mechanical weathering
Chemical Weathering

3. Weathering Mechanical Weathering Chemical Weathering
Physical disintegration of rock
Results in smaller fragments
Chemical Weathering
Internal structure of a mineral is altered
A new mineral is formed

4. Weathering Examples
Mechanical weathering
Chemical weathering

5. Mechanical Weathering
Rocks are broken into smaller pieces without changing the rock’s mineral composition
3 types
Frost wedging
Unloading
Biological activity

6. Mechanical – Frost Wedging
Breaking of rock from freezing and thawing
Mammoth, Twin Lakes (2006)
Repeated expansion and contraction break rock bodies into angular pieces (talus)

7. Mechanical - Unloading
Erosion removes overlying rock
Decreases pressure
Underlying rocks rise and expand
Rocks break off in layers (exfoliation)

8. Mechanical – Biological Activity
Organisms break rock into fragments
Plants
Animals
Humans

9. Chemical Weathering 3 Types
Chemical transformation of rock into one or more new compounds
Feldspar
Kaolinite
3 Types
Oxidation
Hydration
Carbonation

10. Chemical - Oxidation
Oxygen reacts with minerals and forms iron oxide (rust)
Bryce National Park
Results in rocks with a reddish or yellowish coloring

11. Chemical - Hydration Water interacts with minerals and forms clays
Granite composed of silicate minerals (feldspar, hornblende and biotite)
Silicate minerals weather into clays (kaolinite)

12. Chemical - Carbonation
Carbon dioxide combines with water and forms a weak acid (carbonic acid)
Dissolves limestone
Stalactites
Caves
Caves
Limestone
Shells (CaCO3)

13. Rates of Weathering Factors controlling weathering rates
Rock Characteristics
Climate
Differential Weathering

14. Rock Characteristics Composition Particle size Joints & Fractures
Certain rocks are more resistant to weathering
Particle size
Small pieces generally weather faster than larger pieces
Joints & Fractures
Allows water to penetrate between cracks
Marble
Granite

15. Climate
Warm, moist areas tend to weather minerals faster

16. Differential Weathering
Certain rock types are more resistant to weathering
Volcanic neck and dikes are more resistant

17. Which will Weather Faster?
Boulder vs. Pebbles

18. Which Area Will a Faster Rate of Weathering?
Mammoth vs. Maui

19. What Type of Weathering is Displayed?
Oxidation & Differential Weathering