1

Chapter 7- Weathering, Erosion and Soil

 

2

I. Weathering

A. The process by which rocks on or near Earth’s surface break down and change is called weathering.

 1. Removal and transport of weathered material from one location to another is erosion

3

4

2. The process by which rocks and minerals break down into smaller pieces is mechanical weathering- also called physical weathering

5

Physical weathering

6

3. Mechanical weathering does not involve any change in a rock’s composition, only changes in the size and sometimes the shape of the rock.

7

Mechanical weathering

8

B. Factors that are involved in mechanical weathering.

 1. Temperature plays a big role in mechanical weathering.

9

2. Repeated thawing and freezing of water in the cracks of rocks is called frost wedging.

 3. Frost wedging is responsible for potholes.

10

11

4. Pressure is another factor. Over time, layers of rock are stripped away is called exfoliation.

 

12

C. Chemical weathering is when rocks and minerals undergo changes in their composition as the result of chemical reactions.

 1. Some agents, water, oxygen, carbon dioxide, and acids.

13

2. Water can dissolve many kinds of minerals and rocks. Water has an active role in some reactions.

 3. The reaction of water with other substances is known as hydrolysis

14

4. Hydrolysis occurs in the decomposition of silicate minerals.

15

5. Oxygen can combine with other substances oxygen and other substances are called oxidation.

 6. Acid rain also can chemically change some minerals or rocks.

16

D. Affects of rate of weathering. 1.       Natural weathering of earth

materials occurs very slowly.  2.       The climate of an area is a major

influence on the rate of chemical weathering of earth materials. (Temperature, precipitation)

17

E. Rock type and composition 1.       Characteristics of rocks

including how hard or resistant they are to being broken down depend on their type and composition.

18

II. Erosion and Deposition

A. Materials that are dropped in another location is the process of deposition, the final stage of the erosion process.

 1. Gravity is associated with many erosion agents because the force of gravity tends to pull all materials down slope.

19

20

2. Erosion also occurs by running water.

 3. The erosion by running water in small channels, on the side of a slope is called rill erosion.

21

22

4. Rills commonly form on a slope. 

5. When channel becomes deep and wide, it can evolve into gully erosion. (These can be big troubles for farmers)

 6. Erosion also occurs because of costal depositions.

23

Gully Erosion

24

7.   Glaciers also cause erosion 

8.   Wind causes erosion. 

9. Humans, plants and animals cause erosion

25

26

27

III. Soil Formation

A. Soil is almost everywhere on earth. 1.       Soil is the loose covering of broken

rock particles and decaying organic matter, called humus, overlying the bedrock of Earth’s surface.

 2. Soil forms in layers

28

29

2. The solid bedrock from which weatherized pieces of rock first break off is known as parent rock.

 3. Soil located above its parent material is called residual soil.

30

4. Transported soil has been moved to a location away from its parent bedrock.

 5. Things that cause this are erosion, running water, wind and glaciers.

 

31

6. A soil profile is the vertical sequence of soil layers.

32

6. A distinct layer, or zone within a soil profile is called soil horizons.

33

B. Soil Types 1.       The four major types of soil are polar,

temperate, desert and tropical. 

2. Polar soils- form at high latitudes and high elevations in places such as Greenland, Canada, and Antarctica. They have good drainage but no distinct horizons.

 

34

35

3. Temperate soils- varies greatly and is able to support such diverse environments as forests, grasslands, and prairies. Temperate zones have about 50-60cm of water.

36

37

4. Desert soils- receives low amounts of precipitation. Less than 25cm a year. Desert soils are also light- colored, coarse, and many contain salts and gypsum.

38

39

5. Tropical soils- experience high temperatures and heavy rainfall. Tend to have infertile soil. Intense weathering and bacterial activity leave tropical soils with very little humus and very few nutrients. The soil is red in color as a result of oxidation of iron.

 

40

41

C. Soil textures 

1. Particles of soil are classified according to size as being clay, silt or sand with clay being the smallest and sand being the larges.

 

42

D. Soil fertility 1.       Soil fertility is the measure of

how well a soil can support the growth of plants. Factors that affect soil fertility include the available of minerals and nutrients and the number of microorganism.

43

E. Soil color 

1. A soil’s composition and the climate in which it develops are main factors that determine the soil color.

 2. Topsoil is usually dark-colored because it is rich in humus.

44

3.   Color cannot predict fertility. 

4. Red and yellow soils may be the result of oxidation of iron and minerals.

45

5. Grayish or bluish soils are common in poorly drained regions where soils are constantly wet and lack oxygen.

46

47

48

THE END