Geology 101
Name______________________
Reading Guides for Chapters 6 and 12
Chapter 6: Weathering and Soils (p. 160):
This chapter is about the processes involved in the disintegration of rock. Weathering is often mistaken for
erosion which is the removal and transportation of weathered rock materials. These processes are clearly
related to each other, but we will attempt to use these terms correctly. The photograph of Arches National
Park on page 162 shows an arch that was created by both the weathering of the rock and the subsequent
removal of the weathered rock to create the arch.
Weathering (page 162):
What is the difference between mechanical and chemical weathering?
Mechanical Weathering (page 163):
What are some ways in which mechanical weathering occurs?
Chemical Weathering: (p. 166):
For those who have had a chemistry course, you may be able to follow the chemical formulas in this
section, but since most of the students in this class have not had a previous chemistry course, I will not
expect you to know these formulas or be able to use them. If you have questions or would like to know
more about them, see me during an office hour.
In this section three types of chemical weathering are discussed, but the authors did not label these
processes.
The first type of chemical weathering is oxidation. This is formed by the oxidation of iron-rich minerals in
rocks. This oxidation often creates a _____________________ or _______________ color in the soils or
the weathered products.
The second type of chemical weathering is dissolution. In this type of weathering soluble ions are
dissolved by acidic water. What two common types of rocks are most susceptible to this weathering?
How is the acidic water formed in natural environments?
The third type of chemical weathering is hydrolysis. In this type of weathering silica-based rocks, such as
granite are converted to other minerals, such as clay. Hydrolysis is also dependent on acidic water to
initiate the reaction. An important concept is that hydrolysis happens at a faster rate when the temperature
of the water is warmer and when the water is more acidic.
Most sandstones (a common sedimentary rock that we will study later in the quarter) are composed of
grains of quartz sand. Why is quartz more common in sand than the abundance of quartz in un-weathered
rock?
Explain how spheroidal weathering happens.
In review: List the three primary chemical weathering processes:
1)
2)
3)
Rates of Weathering (page168):
►In general, rocks with more mafic minerals (dark colored) will chemically weather ________________
(faster/slower) than more felsic minerals. We can explain this trend because mafic minerals formed at
higher temperatures, so they are the ____________________ (least/most) stable at the earth’s surface.
(Hint: the minerals olivine and pyroxene are most common in mafic rocks, while quartz is most common in
felsic rocks. Use the figure on page 110 and the discussion on page 168 to answer the questions above. If
you need help, let me know.)
►What role does climate have in promoting chemical weathering? What type of climate does chemical
weathering occurs at the fastest rate? Slowest rate?
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Dramatic landscapes are formed in
places such as Bryce Canyon
National Park from differential
weathering and erosion. Explain
why some rocks may weather faster
than others in a place that has the
same climate.
(2 sections) Soil and Controls of Soil Formation (pages170 and 171)
In most places, the Earth’s surface is covered by a layer of weathered debris. This layer is called
_____________________. Soils are a special part of this zone. What is soil? What is humus?
What are the primary controls of soil formation?
The Soil Profile and Classifying Soils (pages 173-175) will not be covered on the exam. If you are a
Natural Resources major or your are considering a major in agriculture, you may want to read these
sections.
Impact of Human Activities on Soil (page 176):
This is an important topic for all of us since our food availability is dependent on healthy soils, but read the
part on Erosion: Losing a Vital Resource.
What is the primary process that erodes soil?
Weathering and Ore Deposits (page 180): You will not be tested over this section, but you might find it
interesting to find out how products such as aluminum foil is mined from weathering products.
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Chapter 12: Mass Wasting: The Work of Gravity (page 318)
The Importance of Mass Wasting (page 320)
Most the concepts in this section are relatively common-sense, but are important in understanding how the
Earth works. On page 321 the diagram of the Grand Canyon indicates that mass wasting is responsible for
most of the erosion in the canyon and only the narrow section directly above the river is due to the
movement of sediment by the Colorado River. Also, one can see the different slopes created by the
differential weathering and erosion of various rock types.
It is also logical the erosion processes tend to produce a flatter landscape over time. If internal processes
that uplift mountains stops, erosion processes reduce the angle of the slopes over time.
Controls and Triggers of Mass wasting (page 322):
We may read a newspaper account of a landslide and the article may something like: “… the slide was
caused by the heavy downpour of rain during the past 24 hours….” In the introduction to this section the
authors make a point that the rain was mostly like a _______________________ and that there could be
multiple causes for a landslide.
What is the role of water in promoting mass wasting?
The angle of repose is defined as:
The angle depends on the ____________________ and ___________________of the particles . It is
important to note that the angle of repose concept applies to ________________________ particles not
consolidated rock slopes.
Besides adding water to slopes and oversteepening, what are two other triggers that may initiate mass
wasting events? Explain how each one initiates a movement.
Some landslides happen without a discernible trigger. What process that we have studies in this reading
guide may be responsible for these mass movements?
Classification of Mass-Wasting Processes (page 326):
The classification of landslides is based on the type of materials, the type of motion, and to some degree the
rate of motion.
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What are the three types of motion of a landslide?
The very slow movement of the regolith is termed ___________________.
Rapid Forms of Mass Wasting and Slow Movements (pages 327 to the end of the chapter)
_____ 1. A mass movement that rotates as a block along a
concave slip plane. Usually occurs in cohesive materials.
_____ 2. Relatively dry mass movements. They ooze
downslope with a relatively high viscosity
_____ 3. The Gros Ventre mass movement is an example.
A. creep
_____ 4. Described as wet concrete to soupy mixture not
much thicker than muddy water. The type most often called a
“mudslide”.
_____ 5. A very slow type of mass movement that affects
slopes at most latitudes. Freezing and thawing is one way this
process occurs.
_____ 6. The fastest type of mass movement occurs when
loose sediment or rocks breaks free
_____ 7. This type of mss movement moves along a defined
slip plane. Normally parts of the mass hold together.
_____ 8. Common in semi-arid regions. Similar to
“mudflows” but particles are larger.
D. slump
What are some characteristics of slumps?
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B. solifluction
C. rock slide
E. debris flow
F. earthflow
G. fall
H. slide