1. Physical (Mechanical) and Chemical Weathering
Created By:
Mr. Kreeger

2. Page References and Homework
Do problems # 1a,b and c, 2a, 3a,b and c, 5a
Do problems # 2b, 5b,c and d
Do problem # 6

3. Table of Contents Weathering Defined Types of Physical Weathering
Frost Wedging
Abrasion
Wetting and drying
Exfoliation
Plant roots
Lichen and moss
Types of Chemical Weathering
Oxidation
Hydrolysis
Carbonic Acid
Factors affecting Weathering
Hardness
Surface area
Climate

4. Introduction Video Clip
Weathering

5. Weathering Defined
Breakdown of rocks into smaller particles by natural processes
Exposure to air, water and living things at or near the surface results in weathering
Two Types
Mechanical Weathering
Chemical Weathering

6. Physical (Mechanical) Weathering Video Clip

7. 1. Types of Physical (Mechanical) Weathering
Physical (Mechanical) Weathering- The breakdown of rocks w/out changing chemical compositions
a. Frost Wedging- Water enters crack Freezes  Expands Forces crack to open wider (Process repeats until rock splits)

8. Eventually, the rock splits from repeated frost action!

9. 1. Types of (Physical) Mechanical Weathering cont…
Abrasion- Process of rocks rubbing against each other
Occurs where fragments of rocks are carried along by streams
Breaks rocks into smaller pieces and makes them more rounded.
Wind also weathers rock by abrasion. (Think about the beach)

10. 1. Types of (Physical) Mechanical Weathering cont…
c. Wetting and drying
breaks up rocks that are made from clay
When they are wet they expand, and they shrink as they dry
As this repeats over and over, the clay becomes weak and cracks (think of all the projects you have made out of clay…they all crack and fall apart)!

13. 1. Types of (Physical) Mechanical Weathering cont…
d. Exfoliation
soil and rock is removed (glaciers or uplifting), exposing rock found deep underground
This releases the pressure causing the surface of the rock to expand and eventually crack

17. 1. Types of (Physical) Mechanical Weathering cont…
e. Plant Roots
The deep roots of trees often break apart rocks
f. Lichen & Moss
These low to the ground plants can grow on rocks and eventually break them apart

19. Introduction Clip to Chemical Weathering

20. 2. Types of Chemical Weathering
Chemical Weathering- The breakdown of rocks by changing their chemical compositions. (The presence of oxygen, water and Carbon Dioxide is most responsible)
a. Oxidation- Oxygen reacts with many minerals especially those containing iron to form rust. (Occurs faster with water)

21. Chemical weathering of basalt

22. Iron Banding in Basalt

23. Oxidative weathering of mineral deposits (new deposits are white/yellow, weathered deposits are reddish-brown)

24. Video Clip about Oxidation

25. 2. Types of Chemical Weathering cont…
b. Hydrolysis
water (hydro) reacts with minerals such as feldspar and form clay

27. 2. Types of Chemical Weathering cont…
c. Carbonic acid
carbon dioxide (CO²) dissolves in water to form this acid
can cause minerals to dissolve, especially those containing calcite

28. “Gnarled Rock” – a formation of limestone chemically weathered by acid rain

30. 3. Factors affecting the rate of weathering
Rocks resistance to weathering (Hardness)
Amount of surface area
Climate

31. 3. Factors affecting the rate of weathering cont..
Hardness and mineral composition- Limestone's most affected while granite is least affected.

32. The central area of rock was less resistant to weathering…thus the “arch” was formed!

34. 3. Factors affecting the rate of weathering cont..
Surface Area
Surface area is the amount of rock surfaces exposed to the atmosphere
Greater surface area increases the rate of weathering
Weathering creates more surface area

36. 3. Factors affecting the rate of weathering cont..
Climate
The temperature and moisture levels in an area over a long period of time.
Cold and Moist- Best for Physical Weathering
Warm and Moist- Best for Chemical Weathering

37. Dry Climate = Mechanical Weathering!
Devil’s Marbles, Australia – Mechanical weathering from wind and sand!

38. Warm Climate = Chemical Weathering
Parthenon – Athens, Greece

40. Video Clip of Humans Impact of Weathering