1. Weathering

2. Two Types of Weathering
Physical (also called Mechanical)
Chemical

3. Physical Weathering
A change in the size or shape of a rock without changing the chemical composition

4. How Does it Happen?
Plant roots break rock
Animals burrow into rock
Water breaks down rock by friction

5. Freeze/thaw- water enters cracks in rocks, freezes and widens crack, melts- occurs again and again- eventually widening rock (also called Ice Wedging)

6. Exfoliation- wind blown particles hit rock, breaking off tiny pieces or sheets

7. Temperature Changes- expansion and contraction of rock can break it into smaller pieces

8. Chemical Weathering
Breakdown of rock by agents that cause chemical changes in rock

9. Oxidation
Produces rust
Oxygen in atmosphere combines with metals in rocks

10. Carbonic Acid
Carbon dioxide in atmosphere combines with water in atmosphere to form carbonic acid

11. Carbonic acid falls on ground and dissolves limestone, marble, or calcite
Can produce caves

12. Hydrolysis
occurs when water, usually in the form of precipitation, changes the chemical composition of a rock and creates less stable rocks that weather more readily.

13. Plant Acids Some plants produce an acid that reacts with rocks
EX- lichen

14. A Brief Review
Look at the following pictures and see if you can determine what type of weathering has occurred (physical or chemical) and then identify the specific process that caused the weathering.

23. Reading Guide
Complete Reading Guide for 12.1

24. Pop Quiz
1. What is weathering?
2. What type of weathering causes breaks in rocks caused by the constant freezing & thawing of ice?
3. True or False. Rust caused by weathering.
4. Can carbon dioxide contribute to weathering?

25. Pop Quiz Mechanical or Chemical Weathering?
5. Limestone dissolved by carbonic acid.
6. Animal burrows dug in rock.
7. Formation of potholes in streets during severe winters.
8. The action of water, salt and air on car fenders.

26. The Rate of Weathering
Chapter 8

27. What affects the rate of weathering?
1. Rock Composition
Type of Rock Rate of weathering
Sedimentary
Metamorphic
Igneous
Quickly
Slowly

28. What affects the rate of weathering?
2. Amount of Exposure - when higher % of rock is at surface of earth the faster it will weather
Which landform will have greater surface area?

29. 3. Climate
Very Cold Climates
Weathering takes place slowly

30. 3. Climate
Dry, Hot Climates
Very slow weathering

31. 3. Climate
Warm, Humid Climates
Chemical weathering fast

32. 3. Climate
Places where daily changes in temperature will accelerate weathering

33. 4. Topography
Altitude and slope of land will effect weathering.

34. What’s the Rate of weathering?

35. Pg 277 in book
Numbers and be ready for a quiz.

36. Quiz What type of rock weathers the fastest?
What type of rock weathers the slowest?
Would one rock or many rocks weather faster?
Would rock weather fast or slow in a hot, dry area?
In what region of the US (NE, NW, SE, or SE) would you find high rates of chemical weathering?

37. SOIL Weathered rock forms sediments
Sediments and organic matter (humus) form
SOIL

38. Soil
Mixture of organic matter and weathered rock that forms over a long period of time

39. Factors affecting soil formation
Climate
Parent rock
Organisms
Relief (slope, topography)
Time

40. Soil Profile
Different layers of soil are called HORIZONS
Horizons together make a PROFILE

42. Soil Horizons
O horizon- uppermost layer, organic matter on top of soil
A horizon- top soil layer, includes plant roots, dark in color, much organic matter
(Also called the Zone of Accumulation)

43. Soil Horizons (cont’d.)
B horizon- under A horizon, lighter in color, some organic matter (roots), some weathered rock
(Also called the Zone of Leaching)
C horizon- under B, mostly weathered rock

44. Parent rock- under C horizon, is the type of rock that weathers and produces the soil

45. Importance of Soil Location
Residual soil- forms and stays in the same place
Transported soil- forms in one place, is moved to another
Transported is common

46. Soil Particles Classified by size 3 particle types
sand = 2.0 mm mm
silt = 0.02 mm mm
clay = less than mm

47. Soil Lab
In groups of 3 or 4.
1. Carefully extract a soil sample using either a soil probe. Top of probe must touch the ground.
2. How many different soil layers do you see?
3. Describe each layer, color, composition (sandy, clay, etc.).
4. Label each layer horizons O-D and define each layer.
5. Which layer does vegetation grow in?
6. Which layer has a large abundance of nutrients?
7. Which layer is composed of leaf litter?
All group members must turn questions and findings.