1. Where are we??? Earth’s matter & structure Rock forming processes
Intro to geology
Plate tectonics
Minerals
Rocks
Igneous rocks
Volcanism
Weathering & erosion
Sediments and Sedimentary rocks
Metamorphic rocks
Rock record and Geologic time
Rock deformation
19. Earthquakes
20. Evolution of continents
21. Exploring Earth’s Interior
17. Earth beneath the ocean, shorelines
12. Mass wasting
13. Hydrologic cycle and Groundwater
14. Streams
15. Deserts & winds
16. Glaciers, Ice Ages
18. Landscapes
22. Energy and Mineral Resources
23. Earth’s environment, Global Change, Human Impacts
Earth’s matter
& structure
Rock forming
processes
Where are we???
Dynamic
motions
External
factors,
resources

2. Chapter 7: Weathering and erosion
Study questions….
1) Overview
2) Physical weathering
3) Chemical weathering
4) Weathering rates
5) Soil basics
Some MC questions….

3. Chapter 7: Weathering and erosion
Study Questions:
1. What is the difference between chemical and physical weathering?
2. What is the difference between weathering and erosion?
3. What are the different types of physical weathering?
4. How does feldspar weather into clay?
5. What are the three main agents of chemical weathering?
6. How does silicate weathering influence climate?
7. What controls rates of weathering (e.g, rock characteristics,temperature, humidity).
8. What is soil? ?

4. weathering erosion mass wasting Chapter 7: 1) Overview
Ways to move material to lower elevations:
weathering
erosion
mass wasting
rock disintegration (physical breakdown)
rock decomposition (chemical alteration)
removal of material by water, wind, ice
Later chapter
transfer of rock & soil downhill

5. Chapter 7: 2) Physical weathering
Physical forces break rock into smaller & smaller
pieces w/out changing mineral composition
4 ways this happens in nature:
Frost wedging
Exfoliation and spheroidal weathering
Thermal expansion
Biological activity

6. Frost wedging How? Where?
Chapter 7: 2) Physical weathering
Frost wedging
Repeated cycles of freezing & thawing can break rock into smaller fragments
How?
Water expands ~ 9% upon freezing
Where?
Mountainous regions w/ daily freeze/thaw cycles

7. Chapter 7: 2) Physical weathering
Frost wedging

8. Chapter 7: 2) Physical weathering
Frost wedging
Talus slopes

9. Why? Manifestation: Expansion of rock from removal/erosion
Chapter 7: 2) Physical weathering
Exfoliation and spheroidal weathering
Expansion of rock from removal/erosion
of overlying rock (“sheeting”)
Why?
Reduction in pressure (since less
overlying weight)
Manifestation:
Slab-like layers/sheets break loose

10. Continued weathering causes rock slabs to separate & fall
Exfoliation and spheroidal weathering
Chapter 7: 2) Physical weathering
Continued weathering causes
rock slabs to separate & fall
HALF DOME, YOSEMITE NATIONAL PARK (California)
“exfoliation domes”

11. Chapter 7: 2) Physical weathering
Exfoliation and spheroidal weathering
Chapter 7: 2) Physical weathering
Another “sheeting” example

12. “Devil’s Marbles” Australia
Chapter 7: 2) Physical weathering
Exfoliation and spheroidal weathering
“Devil’s Marbles” Australia

13. Expansion/contraction of rock
Chapter 7: 2) Physical weathering
Alternating Heat and Cold
Expansion/contraction of rock
from
heating/cooling

14. Expansion/contraction of rock
Chapter 7: 2) Physical weathering
Alternating Heat and Cold
Expansion/contraction of rock
from
heating/cooling

15. Expansion/contraction of rock
Chapter 7: 2) Physical weathering
Alternating Heat and Cold
Expansion/contraction of rock
from
heating/cooling

16. Weathering of rock from activities of
Chapter 7: 2) Physical weathering
Biological activity
Weathering of rock from activities of
organisms
plants
burrowing animals
humans

17. Chapter 7: 2) Physical weathering
Surface area increases due to physical weathering and more surface becomes available for chemical reactions.

18. Carbon dioxide (Hydrolysis) Oxygen (Oxidation)
Chapter 7: 3) Chemical weathering
Chemical weathering:
Processes that break rock components and
internal structures of minerals, making new
minerals
Most important agents in chemical weathering:
Water (Dissolution/Hydrolysis)
Carbon dioxide (Hydrolysis)
Oxygen (Oxidation)

19. How? Dissolving minerals by a liquid agent (such as water)
Chapter 7: 3) Chemical weathering
Water (Dissolution)
Dissolving minerals by a
liquid agent (such as water)
How?
Many minerals are water-soluble
example: Halite (salt), Calcite (calcium carbonate)
Pure water is a weak acid
Water molecules break down from H2O into H+ and (OH-)

20. Decomposition of granite
Water (Hydrolysis)
Chapter 7: 3) Chemical weathering
Decomposition of granite
Granite (mainly quartz + potassium feldspar) +
water
Liberates potassium and silica from feldspar, go into solution
makes kaolinite - this left over mineral is clay
- has water absorbed (=hydration)
- main inorganic part of soil
quartz - very stable, glassy appearance
- carried to sea: beach sand, sand dunes
- cements to form sandstone
See Fig. 7.3

21. Carbon dioxide (Hydrolysis)
Chapter 7: 3) Chemical weathering
Carbon dioxide combines with water to carbonic acid
CO2 + H2O
H2CO3
A small portion dissociates into hydrogen ions and bicarbonate ions:
H2CO3
H H CO3 -
Carbonic acid is a weak + most common natural acid
Speeds weathering rates of feldspar and calcite compared with pure water
See Fig. 7.6

22. Chapter 7: 3) Chemical weathering
See Fig. 7.6
See Fig. 7.6

23. Chapter 7: 3) Chemical weathering
See Fig. 7.6

24. Example Chemical reaction that causes loss of electrons
Chapter 7: 3) Chemical weathering
Oxygen (Oxidation)
Chemical reaction that causes loss of electrons
Example
Iron (Fe) + oxygen (O2) (dissolved in water)
oxygen (O) combines with Fe to form iron oxide
= hematite (Fe2O3)
Oxidation decomposes important minerals:
mineral formula where originates from
olivine (Mg,Fe)2SiO4 Earth’s mantle
pyroxene (Mg,Fe)SiO3 Earth’s mantle
hornblende Ca2(Fe,Mg)5Si8O22(OH)2 Continental rocks
See Fig. 7.8

25. Bedrock characteristics
Chapter 7: 4) Rates of weathering
Several control factors:
Bedrock characteristics
Climate
Topography
Some minerals are more stable than others
Temperature, moisture (vegetation)
freeze-thaw cycles
e.g., gentle or steep slopes
Table 7.15
And 7.2

26. Chapter 7: 4) Rates of weathering
Differential weathering

27. Chapter 7: 4) Rates of weathering

28. Chapter 7: 5) Soil basics
Regolith Layer of rock and mineral fragments produced by weathering that cover most of Earth’s land surface
Soil = decomposed rock +
decayed animal/plant life (“humus”)
water
air
45% 5%
25%
“good soil:”

29. Chapter 7: 5) Soil basics

30. Important Soil-forming factors
Chapter 7: 5) Soil basics
Important Soil-forming factors
Parent material
Climate
Time
Plants/Animals
Slope
affects fertility, weathering rate
temperature & precipitation
longer time thicker soil
organic matter
if too steep little/no soil

31. A few questions…
1. Which of the following processes is not an example of chemical weathering?
A. dissolution of calcite
B. breakdown of feldspar to form kaolinite
C. splitting of a rock along a fracture
D. rusting of a nail

32. A few questions…
2. __________ is a chemical reaction in which an atom or ion loses electrons.
A. Carbonation
B. Exfoliation
C. Hydration
D. Oxidation

33. 3. Which of the following statements is true?
A few questions…
3. Which of the following statements is true?
A. High temperature promotes physical weathering.
B. Frost wedging is a form of chemical weathering.
C. Chemical weathering is promoted by gentle slopes.
D. Clay minerals are produced primarily by physical weathering.

34. A few questions…
4. Which of the following will decrease the rate of chemical weathering of a rock at the Earth’s surface?
A. increasing the amount of acid in the rainwater
B. decreasing the temperature
C. breaking the rock into smaller pieces
D. increasing the amount of surrounding soil

35. 5. Which of the following statements is true?
A few questions…
5. Which of the following statements is true?
A. Silicate weathering and volcanism both increase the amount of carbon dioxide in the atmosphere.
B. Silicate weathering increases and volcanism decreases the amount of carbon dioxide in the atmosphere.
C. Silicate weathering decreases and volcanism increases the amount of carbon dioxide in the atmosphere.
D. Silicate weathering and volcanism both decrease the amount of carbon dioxide in the atmosphere.