Weathering

1. Weathering & Erosion

2. Weathering is the break-up of rock due to exposure to the atmosphere.

3. Erosion Remember: Erosion involves removal and transport.

4. Weathering involves two processes that often work together to decompose or break down rocks.

5. Chemical and MechanicalWeathering!

6. Chemical Chemical weathering, or decomposition, takes place when at least some of the rock’s minerals are changed into different substances.

7. Chemical Chemical processes include rain, acid etching by plants, oxidizing, and demineralizing by water.

8. 5 Agents of Chemical Weathering • Common agents of chemical weathering are water, acids, and air. • These agents weaken the bonds between minerals grains of the rock. • 1. Water – can cause rock to be broken down and dissolve. Can take thousands of years to take place. • 2. Air – the process of oxidation is a chemical reaction in which an element (iron) combines with oxygen, causing rust. • (Weak Acids) - acid precipitation, acids in groundwater, acids in living things.

9. Three Sources of Weak Acids • 3. Acid Precipitation – rain, sleet, or snow that contains a high concentration of acid. Normal precipitation is acidic, acid precipitation contains more acid than normal. • 4. Acids in Groundwater – carbonic acid or sulfuric acid reacts with rocks in the ground, causing a chemical reaction, eating away at the rock. • 5. Acids in Living Things – Lichens produce acids that slowly break down rock.

10. Chemical Weathering

11. Types of Chemical Weathering:Dissolution H2O + CO2 + CaCO3  --> Ca+2 + 2HCO3-water + carbon dioxide + calcite dissolve into calcium ion and bicarbonate ion Dissolution is very common in areas that have a great deal of limestone.  Acidic waters (from pollution or natural) dissolve limestone allowing for additional water to gain entrance.  Can cause sinkholes and dissolution of statutes and grave stones.

12. Hydrolysis Hydrolysis takes place when acid rain reacts with rock-forming minerals such as feldspar to produce clay and salts that are removed in solution. The only common rock-forming mineral that is not affected is quartz, which is a chemically resistant mineral. This is why quartz and clay are the two of the most common minerals in sedimentary rocks. The weird shapes form as water attacks the rock along joints and cracks, leaving rounded lumps of un-weathered rock. The iron-rich minerals in the rock have also oxidised to a brown “rusty” colour.

13. Rusting: The Transfer Of Electrons So finally, what is rust? It is the product of the transfer of electrons from the metal (loss of electrons is called oxidation) to the oxygen molecules (gain of electrons is called reduction). Batteries take advantage of this process of natural decay of metals. However, instead of allowing the metals to decay immediately, they make the electrons travel to the other end of the battery first, and so the current can be made to pass through a circuit.

14. Mechanical Mechanical weathering, or disintegration, involves physically breaking rocks into fragments without changing the chemical make-up of the minerals within them.

15. There are four main sources of power for mechanical weathering. Gravity, Water, Wind, & Waves Of these, water appears to be the leader in changing the surface.

16. If a particle is loosened by weathering, but stays put, its just weathering. If it starts moving, itsErosion. Remember this!: You’ll be quizzed soon! Key Point!

17. Mechanical weathering processes, many of which are erosional, include some of the following.

18. Frost Wedging Frost Wedging is the freezing and thawing of water in cracks.

19. Mechanical Exfoliation Mechanical Exfoliation is the peeling off of sheets of rock as they expand and crack.

20. Crystal Growth Wedging Crystal Growth Wedging involves salt crystals growing from salty waters.

21. Crystal Growth Wedging Crystal Growth Wedging usually occurs near coastlines as it has on this granite.

22. Root Penetration Plant roots have to be strong to survive the elements.

23. Root Penetration Powerful plant roots grow into rock cracks and cause fractures.

24. Abrasion Both wind and water can cause abrasion as rock fragments bounce off each other.

25. Abrasion This “moon looking” picture of an Antarctic rock, shows weathering from the wind blown sands.

26. Glacial Weathering Glaciers and avalanches can cause weathering as ice and rock interact.

27. Other Agents of Weathering Things likeflash floods, mud slides, landslides, and other forms of mass wasting can cause weathering.

28. Erosion Remember: Erosion involves removal and transport.

29. Erosion Rain, wind, and streams are all agents of erosion. Can you think of any others?

30. Quiz Time! Get out a piece of paper and identify if the following involve weathering, erosion, both, or neither.

31. Ready? 1.Waves are crashing on a sand beach. 2.Water expands as it freezes in the cracks of rocks. 3. Pebbles move down a stream with the current.

32. 4. Acid rain causes the decomposition of a statue in New York. 5. A man shovels dirt to plant a tree. 6. A Glacier slowly moves down a mountain. 7. A tree’s roots grow into the cracks of rocks. 8. A major volcano erupts.

33. 9. A boy takes out the garbage for his mother. 10. A shovel is left outside and begins to rust. Once you’ve answered these, discuss you’re answers with the rest of the class before you go on.

34. Let’s Discuss The Questions. 1. As the sand is moving there is definitely erosion; there is also abrasion from the sand gains colliding. Both

35. 2. This is frost wedging so it’s mechanical weathering. There is no mention of movement. Weathering

36. 3. There is probably some weathering, but there is definitely erosion. Erosion or Both

37. 4. Acid rain on a statue is chemical weathering. This is mainly Weathering.

38. 5.Since the man is transporting Earth materials, it’s Erosion.

39. 6. A glacier moving down a mountain would have both weathering and erosion. Both

40. 7. A tree’s roots growing into cracks of rocks would be weathering. Weathering

41. 8. A major volcanic eruption would involve both weathering and erosion. Both

42. 9. Unless the garbage has “Earth Material” or dirt in it there is probably no erosion or weathering. Neither

43. 10. The rusting of a shovel is oxidation. This is chemical weathering. Weathering Think you understand the difference?