Weathering

1. Weathering How are the earth’s surfaces changed?

2. Weathering isthe breaking down of rocks and other materials on the earth’ssurface. There is no change in the rock’s chemical make-up or composition with this.

3. There are two types of weathering.

4. Types of Weathering Mechanical or physical weathering~ causes: • Temperature changes causing ice or frost wedging • Root, organic, or biological weathering • Gravity • Abrasion (scraping or sanding) • Unloading or exfoliating (like peeling)

5. Second Type of Weathering Chemical or physical weathering ~causes: • Water wears down rocks • Acid dissolves Earth’s surfaces • Air pollution • Plant chemicals • Oxidation (exposure of minerals to oxygen)

6. Mechanicalandchemicalweathering can work together…

7. Mechanical or physical weathering Causesof mechanical weathering include: • Temperature: which causes cycles of expansion and contraction

8. Mechanical/physical weathering Ice or frost wedging (frost action, freeze-thaw cycle): when liquid water goes into cracks and then freezes causing the cracks to get wider

9. The power of the freezing and warming cycle

10. Moremechanical or physical weathering Organic activity root-pry, burrowing animals, human activities

11. A hearty growing plant can expand a crack in a rock until it splits! CRACK! Roots can also raise up cement slabs, crack sewer lines, and house foundations. Don’t you think they could also crack a rock?

12. Gravitycauses rocks to fall and collide with other rocks Mudslides and sinkholes…

13. Landslides, rockslides, holes, and cracks

14. Abrasion: wearing away by solid particles Wave rock, Australia – carved by wind blown sand.

15. Unloading: the expanding of high pressure rock when exposed to a lower pressure Classic sheeted granite in Yosemite National Park. It is broken into gently dipping plates by unloading joints.

16. Exfoliation or unloading - rock breaks off by layers or sheets along joints parallel to the ground surface; caused by expansion of rock due to uplift and erosion; removal of pressure of deep burial

17. Extreme exfoliation!

18. Contraction due to crystallization The surface pattern on this pedestal rock is honeycomb weathering, caused by salt crystallization. This example is on the island of Taiwan. Salt weathering of building stone on the island of Gozo, Malta

19. The other kind of Weathering~Chemical Weathering The altering of the composition or the make-up of minerals within a rock that results in a reduction in size.

20. Example: Agents of chemical weathering include: • Water: Dissolves minerals out of rocks making them weaker.

21. Chemical weathering Acid: Dissolves minerals in rocks (examples: carbonic acid, acid rain, and plant acid) Cave wall

22. Lichens such as these growing on the rocks in the pictures can produce weak acids that react with the rock.

23. Air polllution can produce acid rain.

24. Picture it… 3000 year old Egyptian Obelisk after 100 years in NY 3000 year old Egyptian Obelisk

25. The ancient Parthenon in Greece shows discoloration and chemical weathering effects just from air pollution and acid rain.

26. More chemical weathering • Oxidation: Oxygen combines with iron minerals and sulfur minerals changing the composition of the rock Oxidation turned these rocks in Nevada's Valley of Fire red.

27. Look at factors that hasten weathering: 1. How much surface area is exposed to the elements?

28. In which shape will weathering occur faster?

29. 2. Climate: Warm, wet climates + chemical weathering breaks down rocks rapidly, too. Mechanical weathering + cold climatesbreak down rocks rapidly.

30. 3. Topography: the position of the rock (Is it in a position where gravity can pull it down?) 4. Air pollution 5. Exposure time (Will the elements have time to break down the surface?) Mechanical and chemical weathering work together to break down rocks and our earth surface.