WEATHERING AND SOIL 6
INTRODUCTION
Weathering and Soils
CHAPTER OUTLINE
1.
2.
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3.
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4.
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5.
Regolith
Soil
6.
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8.
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order series
9.
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LEARNING OBJECTIVES/FOCUS ON CONCEPTS
6.1 Define distinguish
6.3 Discuss
6.5 Define explain
6. Sketch, label, and describe
6.9 Discuss
TEACHING STRATEGIES
Clicker Questions:
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Muddiest Point:
A. Chemical and Mechanical Weathering Examples
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B. Rates of Weathering
C. Soils
TEACHER RESOURCES
Web Resources:
Weathering
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Soils
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Imagery, Animations, and Video Resources:
Images
Weathering and Erosion Images
Animations and Videos
Weathering and Climate
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ANSWERS TO QUESTIONS IN THE CHAPTER:
CONCEPT CHECKS
6.1 WEATHERING
2. Mechanical weathering is the breakdown of rock into smaller pieces, without any change in
6.2 MECHANICAL WEATHERING
1. The mechanical weathering of rock creates increased surface area because this process breaks
2. Water can cause mechanical weathering through wedging, and through the precipitation of
salts. When water freezes, it expands, andwater that freezes within the pores and cracks of
3. An exfoliation dome forms in igneous rocks, especially granite, as overlying Earth materials
5. Activities of organisms can break down and move Earth materials. Roots can wedge into rock
bodies, breaking them into fragments. Burrowing organisms break down rock and solid, and
6.3 CHEMICAL WEATHERING
1. Carbonic acid is formed when carbon dioxide dissolves in water. This carbon dioxide can
2. The reaction of calcite-rich rocks with carbonic acid creates calcium ions and bicarbonate
4. Minerals especially susceptible to weathering include iron-rich minerals such as olivine,
5. Angular masses of rock are often heavily jointed. As water enters these joints, chemical
6.4 RATES OF WEATHERING
1. The headstones in Figure 6.13 weather differently due to their composition. The granite
2. Climate influences the rate of weathering through temperature and available moisture. Areas
6.5 SOIL
1. Soil forms at Earths surface where the geosphere, atmosphere, hydrosphere, and biosphere
2. is a term used for the layer of loose rock and mineral fragments, created by
weathering processes, at the surface of the Earth. Soil is mineral and organic matter, along
6.6 CONTROLS OF SOIL FORMATION
2. The most influential factor in soil formation is climate because variations in temperature and
precipitation will determine the amount, rate, and relative importance of mechanical and
3. The direction of a slope influences the amount of sunlight a slope receives. In the Northern
Hemisphere, south-facing slopes receive much more sunlight than north-facing slopes. Because
6.7 THE SOIL PROFILE
2. Eluviation is the process of fine-grain materials washing out of the E horizon by percolating
waters. These fine materials move downward to the B horizon. Leaching is the process of
6.8 CLASSIFYING SOILS
1. Because environmental conditions vary by location, and through time, many different types of
2. In the contiguous United States, mollisols, ultisols, and aridisols seem to be most extensive.
Mollisols are dark, soft soils that form in prairie areas and hardwood forests. These have
excellent soil fertility. Ultisols are soils representative of long periods of weathering and are
6.9 THE IMPACT OF HUMAN ACTIVITIES ON SOIL
1. Soils in tropical rain forests are not suitable for farming because they are heavily leached; this
leaching leaves very little nutrients in the soil for vegetation growth. Nutrients that are in the
2. The order of soil erosion by water, from the dislodging of particles to the transport of those
3. Human activities have increased the rate of soil erosion by removing vegetative cover through
4. Soil erosion can be controlled in many ways. In agriculture and cultivated areas, these include:
constructing terraces on steep slopes to slow runoff and increase infiltration of water; planting
crops parallel to contours of slopes to slow runoff; adding strips of grass or cover crops to slow
EYE ON EARTH
EOE #1 GRANITE IN THE SIERRA NEVADA
1. This process occurs as granitic rock expands upon removal of overlying material. When
2. This process is called sheeting. The feature created from this process is called an
EOE #2 GRANITE WEATHERING
1. As granite undergoes chemical weathering, hydrolysis will chemically break down the
feldspar minerals into the residual clay mineral kaolinite and silica dissolved in solution.
2. The quartz minerals in the rock will not break down chemically, but will be released from
EOE #3 ROUNDED BOULDERS
1. These highly jointed rocks were once angular, with sharp corners and edges. As water
infiltrated the joints and fractures, chemical weathering acted on surfaces deeper within
2. The process that transformed the angular blocks of rock to rounded boulders is called
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EOE #4 MARBLE CANYON, ARIZONA
1. These rocks likely get their color from iron oxides. These iron oxides form when small
2. In this image, we see abundant loose material at the base of the rocks, but very little plant
EOE #5 RED SOIL
1. The soil shown is likely an oxisol. Its red coloring suggests oxidation of iron; oxisols are rich
in iron and aluminum oxides.
GIVE IT SOME THOUGHT
1. In this image, mechanical weathering is represented by the broken-down glass fragments.
These were likely once intact bottles, and have been broken to smaller pieces over time.
2. Plants promote mechanical weathering through root wedgingroots of plants exert force on
Earth materials, causing them to break into smaller fragments. This breakdown of material
3. Warm, wet conditions are favorable for chemical weathering; this type of weathering will
predominate in this area. The feldspars in the granite would weather relatively quickly
4. Increased CO2 in the atmosphere will likely accelerate chemical weathering in several ways.
First, CO2 in the atmosphere combines with rainwater to create carbonic acid; increased CO2
in the atmosphere will favor the production of more carbonic acid, creating more acidic
5. Feldspars are rare in sedimentary rocks because they are not resistant to weathering at
Earths surface. Through hydrolysis, feldspar minerals in rock quickly break down into
6. These features are now exposed at the surface due to differential weathering. Rocks do not
weather uniformlysome minerals are more susceptible to weathering than others. The
7. To determine how rapidly a structure might deteriorate, you would need to know its
composition. Once its composition is known, a review of the climate of your area would tell if
8. Similarly to carbon dioxide in the atmosphere, sulfur dioxide can combine with water in the
atmosphere to produce acidic atmospheric water and acid rain. High concentration of SO2
9. The term is inaccurate; is a more accurate term. is a term
that describes an accumulation of weathered rock fragments at the surface. A true soil is a
10. This soil is very dark, indicating abundant humus (decomposed plant matter). Therefore, it
11. The main soil order in the region adjacent to South Americas Amazon River is oxisols. This
soil type is a product of strongly weathered materials and is characterized by heavy
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12. Tropical areas support dense vegetation because nutrients are continuously recycled from
biomass to living plants. Abundant moisture and warm temperatures favor high rates of
chemical weathering; plant remains decay and oxidize very quickly in these regions and
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