2. External Processes
Erosion Weathering

3. Weathering
Weathering - forces that are changing rocks and land over time, even day to day.

4. Mechanical Weathering
Mechanical weathering – when a force breaks a rock into smaller pieces by forcing them apart.
Breaking large rocks into smaller ones

5. Causes of Mechanical Weathering
Roots growing through rocks - root wedging
ice get into rocks – frost wedging
Thermal expansion

6. Effects of Mechanical Weathering
Stone Mountain, GA
Grand Canyon

7. Chemical Weathering
Chemical weathering - when something "eats away" at a rock rather than breaking it apart.
Must have a chemical change in the rocks

8. Causes of Chemical Weathering
1. Acid Rain

9. Regions Sensitive to Acid Rain

10. Causes of Chemical Weathering
2. Water – creates a chemical reaction in certain rocks
3. Chemicals – resulting from pollution or internal processes
Foaming pollution on rocks.

11. Effects of Chemical Weathering
At PH1, this New Zealand lake is pure hydrochloric acid
Naked trees
Rust

12. Analysis
What is the key difference between mechanical and chemical weathering?
Create a weathering wonderland.
Sketch a landscape that includes examples of weathering resulting from each of the 6 causes. (3 mechanical, 3 chemical)
Label each cause

13. Rocks that have split apart due to thermal expansion.

14. Erosion
Erosion - the removal of ground materials (soil, sand, rocks) by water or wind.

15. Glaciers – how they form

16. Erosion
1. Glaciers  a large, slowly moving, river of ice

17. Example: Iceland - Glaciers are very powerful.
- They carve out huge chunks of land forming canyons and valleys thus creating mountains out of flat land.

18. Effects of Glaciers
Appalachian Mountains - Old
Alaska - New

19. Receding Glaciers Explain this map of Glacier Bay in Alaska.
What does it suggest?

20. Effects of Receding Glaciers
1. What does this graph suggest?
2. What types of decisions might a geographer make based on this data?

21. Wind Erosion
Wind blows the small particles exposing the larger rocks below and smoothing them down.

22. Wind Erosion – check this out