1. External Forces

2. By Today’s End By today’s end you should know the following:
The definition of external forces
The definition of weathering and erosion
Examples of how weathering and erosion occur

3. Weathering
The breakdown ofthe materials of Earth’s crust into fragments.

4. Physical Weathering
Process by which rocks are broken down into smaller pieces by external conditions.
Types of Physical weathering
Frost
Plant roots
Friction and impact
Burrowing of animals
Temperature changes

5. Frost Wedging

6. Plant Roots

7. Friction and Repeated Impact

8. Burrowing of Animals

9. Temperature Changes

10. Chemical Weathering
The process that breaks down rock through chemical changes.
The agents of chemical weathering
Water
Oxygen
Carbon dioxide
Living organisms
Acid rain

11. Water
Water weathers rock by dissolving it

12. Oxygen
Iron combines with oxygen in the presence of water in a processes called oxidation
The product of oxidation is rust

13. Carbon Dioxide CO2 in rain water and creates carbonic acid
Carbonic acid easily weathers limestone and marble

14. Living Organisms
Lichens that grow on rocks produce weak acids that chemically weather rock

15. Acid Rain
Compounds from burning coal, oil and gas react chemically with water forming acids.
Acid rain causes very rapid chemical weathering

16. Name a process of weathering

17. Erosion
Unlike weathering which breaks down rocks into fragments where they are, erosion wears down surface materials and moves them from one place to another.
Erosion is driven by water, ice, wind or gravity and it moves fragments of rock and soil.

18. Water Erosion
Rivers, streams, and runoff

19. Ice Erosion
Glaciers

20. Wind Erosion

21. Mass Movements Landslides, mudslides, slump and creep
landslide clip.mpeg