1. Weathering & Soil Formation
4.1
Mechanical and Chemical
Forces Break Down Rocks

2. Preview of 4.1
Weathering

3. Preview Cont…
Mechanical Weathering
Ice Wedging

4. Preview Cont…
Pressure Release
Exfoliation
Plant Root Growth

5. Preview Cont…
Abrasion
Chemical Weathering

6. Preview Cont…
Dissolving
Rusting

7. Preview Cont…
Surface Area
Rock Composition
Climate

8. Key Terms Weathering Mechanical Weathering Exfoliation Abrasion
Chemical Weathering

9. Weathering breaks rocks into smaller pieces
Tiny rocks. How do rocks get small?
Over time natural forces break rocks down
Sidewalks or driveways cracked
Weathering
Process by which natural forces break down rocks
Two kinds-mechanical and chemical

10. Mechanical weathering produces physical changes in rocks
Breaking up of rocks by physical forces
Rocks split apart
Doesn’t change composition
Types of Mechanical Weathering
Ice Wedging
Pressure Release
Plant Root Growth
Abrasion

11. Ice Wedging Water freezes and expands
Cracks or pores of rocks and forces expansion that is strong
Can break huge boulders
Occurs where temps rise and fall around the freezing point

12. Ice Wedging

13. Pressure Release
Rock is under great pressure and pushed up to surface of earth
Great pressure inside of rock causes expansion
The rock will crack and break
Exfoliation
Process in which layers or sheets of rock gradually break off
Onion skin weathering

14. Exfoliation

15. Plant Root Growth Trees, bushes and other plants take root in cracks
Roots expand and break rocks

16. Plant Root Growth

17. Abrasion Water can wear down rocks on riverbeds or shorelines Abrasion
Process of wearing down by friction, the rubbing of one object or surface against another
Tumbling-moving and grinding against eachother

18. Abrasion

19. Chemical weathering changes the mineral composition of rocks
Rusty nail=chemical reaction/change
steel contains iron mixes with oxygen and water to form rust
Mix with water and air
Chemical weathering
Breakdown of rocks by chemical reactions that change the rocks makeup or composition.
Minerals in rock contact air/water

20. Dissolving Water main cause
In the atmosphere, small amounts of carbon dioxide dissolve in rainwater.
The water and carbon dioxide react to form a weak acid.
After falling, the water moves through the soil picking up additional carbon dioxide from decaying plants.
This acid water breaks down minerals in rocks, and may break them apart.
Air pollution from cars and power plants can make rainwater even more acidic.

21. Acid Rain

22. Rusting Oxygen is also involved in chemical weathering.
Oxygen, water, and dissolved minerals containing iron produce iron oxides, or rust.
Iron oxides form a coating that colors weathered rocks

23. Rusting

24. Weathering occurs at different rates
Most weathering occurs over long periods of time- hundreds, thousands, or even millions of years.
It takes hundreds or thousands of years for a very hard rock to wear down just a few millimeters (the thickness of your fingernail).
Not all rocks wear at the same rate. Factors affecting the rate of weathering include, the rock’s size (surface area), the composition (granite vs. limestone) and the climate that the rock is in (hot, wet regions weather rocks faster than cold, dry ones).