Physical (Mechanical) and Chemical Weathering

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

2. Page References and Homework • Page References • Page 131-136 • 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. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Which acitivity demonstrates chemical...

20. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Landscapes will undergo the most chem...

21. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Rock samples brough back from the mmo...

22. Introduction Clip to Chemical Weathering

23. 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)

24. Chemical weathering of basalt

25. Iron Banding in Basalt

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

27. Video Clip about Oxidation

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

30. 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

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

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

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

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

37. 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

39. 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

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

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

42. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Which geologic feature is caused prim...

43. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Which change in climate would most li...

44. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Water is a major agent of chemical we...

45. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Which typ of climate has the greates ...

46. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: In which climate would chemical weath...

47. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Which process involves either a physi...

48. Don’t forget: You can copy-paste this slide into other presentations, and move or resize the poll. Poll: Which property of water makes frost a...

50. Video Clip of Humans Impact of Weathering