1.intro to geology 2.plate tectonics 3.minerals 4.rocks 5.igneous rocks 6.volcanism 7.weathering...

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 Frost wedging

Talus slopes

Chapter 7: 2) Physical weatheringChapter 7: 2) Physical weathering Frost wedging


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



Continued weathering causesrock slabs to separate & fall

HALF DOME, YOSEMITE NATIONAL PARK (California)

“exfoliation domes”


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


Biological activity

Weathering of rock from activities of

organisms plants burrowing animals humans



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)


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


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


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


See Fig. 7.6See Fig. 7.6


See Fig. 7.6

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


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

Differential weathering


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


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


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.


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


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.


1.intro to geology 2.plate tectonics 3.minerals 4.rocks 5.igneous rocks 6.volcanism 7.weathering...

Documents

physical weathering

weathering erosion

spheroidal weathering

weathering rates

weathering causes rock

rates of weathering

f frost wedging f exfoliation

ice slide