1. Intro to geology2. Plate tectonics3. Minerals4. Rocks5. Igneous rocks6. Volcanism7. Weathering & erosion8. Sediments and Sedimentary rocks9. Metamorphic rocks10. Rock record and Geologic time11. Rock deformation19. Earthquakes20. Evolution of continents21. Exploring Earth’s Interior17. Earth beneath the ocean, shorelines12. Mass wasting13. Hydrologic cycle and Groundwater14. Streams15. Deserts & winds16. Glaciers, Ice Ages18. Landscapes22. Energy and Mineral Resources23. Earth’s environment, Global Change,
Human Impacts
Earth’s matter& structure
Rock formingprocesses
Dynamicmotions
Externalfactors,resources
Where
are
we??
?
1) Overview
2) Physical weathering
3) Chemical weathering
4) Weathering rates
5) Soil basics
Chapter 7: Chapter 7: Weathering and erosionWeathering and erosion
Some MC questions….
Study questions….
Chapter 7: Chapter 7: Weathering and erosionWeathering 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?
3. 4. How does feldspar weather into clay? 4. 5. What are the three main agents of chemical weathering?5. 6. How does silicate weathering influence climate? 6. 7. What controls rates of weathering (e.g, rock
characteristics,temperature, humidity). 7. 8. What is soil?
?
Later chapter
weathering
erosion
mass wasting
Chapter 7:Chapter 7: 1) Overview 1) Overview
Ways to move material to lower elevations:Ways to move material to lower elevations:
rock disintegration (physical breakdown) rock decomposition (chemical alteration)
transfer of rock & soil downhill
removal of material by water, wind, ice
Chapter 7: 2) Physical weatheringChapter 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
Frost wedging
Repeated cycles of freezing & thawing can break rock into smaller fragments
How?How?
Water expands ~ 9% upon freezing
Where?Where?
Mountainous regions w/ daily freeze/thaw cycles
Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering
Exfoliation and spheroidal weathering
Expansion of rock from removal/erosionof overlying rock (“sheeting”)
Why?Why?
Reduction in pressure (since lessoverlying weight)
Manifestation:Manifestation:
Slab-like layers/sheets break loose
Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering
Exfoliation and spheroidal weathering
Continued weathering causesrock slabs to separate & fall
HALF DOME, YOSEMITE NATIONAL PARK (California)
“exfoliation domes”
Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering
Another “sheeting” example
Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering Exfoliation and spheroidal weathering
“Devil’s Marbles” Australia
Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering Exfoliation and spheroidal weathering
Alternating Heat and Cold
Expansion/contraction of rock
from
heating/cooling
Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering
Alternating Heat and Cold
Expansion/contraction of rock
from
heating/cooling
Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering
Alternating Heat and Cold
Expansion/contraction of rock
from
heating/cooling
Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering
Biological activity
Weathering of rock from activities of
organisms plants burrowing animals humans
Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering
Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering
Surface area increases due to physical weathering and more surface becomes available for chemical reactions.
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)
Water (Dissolution)
Dissolving minerals by aliquid agent (such as water)Dissolving minerals by aliquid agent (such as water)
How?How?Many minerals are water-soluble example: Halite (salt), Calcite (calcium carbonate)
Chapter 7: 3) Chemical weathering
Pure water is a weak acid
Water molecules break down from H2O into H+ and (OH-)
Water (Hydrolysis)
Decomposition of graniteDecomposition 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
Chapter 7: 3) Chemical weathering
See Fig. 7.3
Carbon dioxide (Hydrolysis)
Carbon dioxide combines with water to carbonic acidCarbon dioxide combines with water to carbonic acid
H2CO3
Carbonic acid is a weak + most common natural acid
Speeds weathering rates of feldspar and calcite compared with pure water
Chapter 7: 3) Chemical weathering
See Fig. 7.6
H+ + H CO3
-
A small portion dissociates into hydrogen ions and A small portion dissociates into hydrogen ions and bicarbonate ions: bicarbonate ions:
CO2 + H2O
H2CO3
Oxygen (Oxidation)
Chemical reaction that causes loss of electronsChemical reaction that causes loss of electrons
ExampleExample
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
Chapter 7: 3) Chemical weathering
See Fig. 7.8
Bedrock characteristics
Climate
Topography
Chapter 7: 4) Rates of weathering
Several control factors:Several control factors:
Some minerals are more stable than others
Temperature, moisture (vegetation) freeze-thaw cycles
Table 7.15And 7.2
e.g., gentle or steep slopes
Chapter 7: 5) Soil basics
Soil = decomposed rock + decayed animal/plant life (“humus”) + water + air
45%
5%
25%
25%
“good soil:”
Regolith Layer of rock and mineral fragments produced by weathering that cover most of Earth’s land surface
Important Soil-forming factors
Parent material
Climate
Time
Plants/Animals
Slope
temperature & precipitation
organic matter
longer time thicker soil
if too steep little/no soil
Chapter 7: 5) Soil basics
affects fertility, weathering rate
1. Which of the following processes is not an example of chemical weathering?
A. dissolution of calcite B. breakdown of feldspar to form kaoliniteC. splitting of a rock along a fractureD. rusting of a nail
A few questions…A few questions…
2. __________ is a chemical reaction in which an atom or ion loses electrons.
A. Carbonation B. ExfoliationC. HydrationD. Oxidation
A few questions…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.
A few questions…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 rainwaterB. decreasing the temperatureC. breaking the rock into smaller pieces D. increasing the amount of surrounding soil
A few questions…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.
A few questions…A few questions…