1. Ch 10:
Weathering and
Soil Formation

2. What is weathering?
Rocks on the Earth’s surface undergoing changes in appearance and composition

3. What are the 2 types of Weathering?
Mechanical-
physically changing rock into smaller pieces without changing its composition
Chemically-
breakdown of rock by changing its chemical composition

4. mechanical weathering?
What are the types of
mechanical weathering?

5. Types of Mechanical Weathering
1. Exfoliation (unloading)- process where sheets of rock peel or flake away

7. Example of exfoliation:

8. Types of Mechanical weathering
2. Ice wedge- occurs when water seeps into rocks and freezes

11. Ice wedging

12. Types of Mechanical weathering
3. Biological activity- the activity of organisms, including plants, burrowing animals, and humans that weather away rock

13. Weathering by plants

15. Weathering by sandmartins nesting in cliff

16. Types of Mechanical weathering
4. Abrasion- collision of rock with one another resulting in breaking and wearing away.

17. Abrasion takes place in many environments:
fast-moving streams
beaches subject to storm waves
desert environments with high winds
beneath glaciers that are loaded with fragments of rock.

18. Water-carried particles eating away at the rock

19. Storm waves have eaten away at the shoreline

20. The ocean waves have eroded this beach leaving behind a cliff as the soil was washed away

21. Observe the effects of mechanical weathering.

22. What are the Types of
Chemical Weathering?

23. Types of Chemical Weathering
1. Hydrolysis:
Change in composition of minerals when they react with water

24. Feldspar combines with H2O to form a common clay called kaolin

25. Types of Chemical Weathering
2. Carbonation –
When some minerals come in contact with carbonic acid, they form a new product

26. Stalactites caused by carbonation
Limestone is eaten away by acid and deposits as it drips from ceiling of cavern

27. Types of Chemical Weathering
3. Oxidation –
When metallic elements combine with oxygen

28. Oxidation = rust!

29. Types of Chemical Weathering
4. Acid Precipitation
“acid rain”

31. Types of Chemical Weathering
5. Plant acids – plants secrete acids that erode away the rock

32. Lichens and mosses grow on rocks and secrete weak acids that dissolve the surface

33. What 4 things affect the rate of weathering?

34. 1. Rock composition
Igneous and metamorphic rocks don’t weather easily
Sedimentary rocks do

35. 2. Amount of exposure
More exposure it receives, faster it will weather
Amount of time and amount of surface area exposed is also important

37. 3. Climate
Slow in very hot / very cold climates
Fairly rapid in warm, humid climates

38. Cleopatra’s needle after only one century in New York City

39. 4. Topography
Elevation or slope of surface where rock is located affects rate of weathering