Test 2 Chapter 8

Question 1

List examples of Earth’s internal and external processes.

Answer 1

External processes include weathering, mass wasting, and erosion. Internal processes
include mountain building, volcanic activity.

Question 2

From where do internal and external processes derive their energy?

Answer 2

External processes derive their energy from the Sun, while internal processes derive their
energy from Earth’s interior.

Question 3

Contrast mechanical and chemical weathering.

Answer 3

Mechanical weathering involves breaking rocks into smaller and smaller pieces without
changing the rock’s mineral composition. By contrast, chemical weathering involves a
chemical transformation of rock components into one or more new compounds

Question 4

When a rock is mechanically weathered, how does its surface area change? How does this
influence chemical weathering?

Answer 4

As rocks are broken in smaller pieces by mechanical weathering, the exposed surface area
increases. Therefore, more surface area is available for the reactions of chemical
weathering to act upon and chemical weathering is more efficient.

Question 5

How is carbonic acid formed in nature? What products result when carbonic acid reacts
with potassium feldspar?

Answer 5

As rainwater falls through the atmosphere, carbon dioxide can dissolve in the water
producing carbonic acid. Carbon dioxide can also dissolve in water as the water percolates
into soil as decaying matter in the soil releases carbon dioxide. When carbonic acid reacts
with potassium feldspar, the products that result are residual clay, potassium ions in
solution, and soluble silica in solution.

Question 6

Distinguish between four types of mechanical weathering.

Answer 6

Frost Wedging: Freezing water expanding in cracks, or lenses of water growing
bigger as they attract more water, gradually weakens a rock causing it to fracture
Salt Crystal Growth: As sea spray or salty groundwater seeps into crack and pore
spaces of a rock and the water evaporates. As the water evaporates, salt crystals
forma and weaken the rock by exerting pressure to separate mineral grains or
enlarge cracks.
Sheeting: When over lying rock is eroded away from on top of a rock body, the
great reduction in pressure allows the outer parts of the rock body to expand
more than the rock body below and separate from the rock body in sheets.
Biological Activity: One example is growing plant roots wedging rocks apart.

Question 7

Explain how angular masses of rock often become spherical boulders.

Answer 7

Because weathering attacks and wears down corners and edges of blocks faster than flat
surfaces, angular blocks lose their sharp edges and become smooth and rounded. Although
the spherical rock is still weathering, all surfaces are weathering at the same rate.

Question 8

List three or more factors that influence the type and rate of weathering.

Answer 8

Factors that influence the type and rate of weathering include: rock characteristics,
climate, and human activities.

Question 9

Explain why soil is considered to be an interface in the Earth system.

Answer 9

Soil is considered an interface in the Earth system because soil forms at Earth’s surface
where the geosphere, atmosphere, hydrosphere, and biosphere meet, or interface.

Question 10

How is regolith different from soil?

Answer 10

Regolith 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
with water and air that support plant growth. Regolith would not be considered soil unless
it also contained humus (decayed remains of plant and animals) and thus could support
plant growth.

Question 11

Why is texture an important soil property?

Answer 11

Texture is an important soil property because it strongly influences the soil’s ability to
retain and transmit both water and air.

Question 12

List the five basic controls of soil formation.

Answer 12

The five controls of soil formation are parent material, climate, plants and animals,
topography, and time.

Question 13

Which factor is most influential in soil formation?

Answer 13

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 chemical weathering processes.

Question 14

How might the direction a slope is facing influence soil formation?

Answer 14

The slope orientation (or slope aspect) affects the amount of sunlight received. This, in turn,
affects the soil temperature and the amount of moisture retained in the soil, which, in turn,
affects the amount of vegetation and ultimately the soil formation.

Question 15

Describe the following features or processes: eluviation, leaching, zone of accumulation,
and hardpan.

Answer 15

Eluviation is the process of fine-grain materials washing out of the lower A and upper
B horizon by percolating waters, creating a distinctive E horizon. These fine materials move
downward to the lower B horizon. Leaching is the process of water dissolving soluble
inorganic soil components and moving them downward to deeper layers. The B horizon,
then, becomes the zone of accumulation as this is the layer where the fine materials and
some of the soluble materials accumulate. If large quantities of clay materials accumulate
in the B horizon, hardpan can be formed. Hardpan is a very compact and impermeable B
horizon created by abundant clay accumulation.

Question 16

Why are soils classified?

Answer 16

Because soil type can be highly varied, a classification system brings order to large
amounts of information, which aids in understanding and facilitates analysis and
application.

Question 17

What are three particularly extensive soil orders in the 48 United States? What are two soil
orders in Alaska?

Answer 17

The three most extensive soil orders in the lower 48 states are mollisols, ultisols, and
aridisols. In Alaska, gelisols and inceptisols are dominant. Gelisols are young soils with
little profile development due to slow soil-forming processes; these occur in areas of
permafrost. Inceptisols are weakly developed young soils; in these soils, profile
development is just beginning.

Question 18

Link these phenomena in a description of soil erosion: sheet erosion, gullies, raindrop
impact, rills, and streams.

Answer 18

Raindrop impact exerts force on the top layer of soil, mobilizing it. Flowing water forms
thin sheets that move the soil; this is called sheet erosion. Tiny channels called rills form
after this sheet layer has been flowing a short distance, and eventually deeper channels
called gullies are created. As the soil particles are washed out, they move downslope into a
stream.

Question 19

How have human activities affected the rate of soil erosion?

Answer 19

Human activities have increased the rate of soil erosion by removing vegetative cover
through construction, logging, agriculture, and urbanization. The removal of vegetation
increases the rate of soil erosion because it exposes soil particles to easy transport by water
and wind.

Question 20

Briefly describe three methods of controlling soil erosion

Answer 20

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 runoff, increase infiltration, and trap sediment; creating grassed
waterways to prevent formation of gullies and trap soil washed from croplands; leaving
crop residues on fields to protect surfaces from water and wind erosion; and planting rows
of trees and shrubs to act as windbreaks and prevent soil erosion in windy areas.

Question 21

What force is responsible for mass movement?

Answer 21

Gravity is the force responsible for mass movement.

Question 22

Describe the role of mass movement in landscape development.

Answer 22

Mass movement transfers weathered debris downslope where other agents, such as streams
or glaciers, transport the material away. In this way mass movement combines with eroding
agents to shape landforms and develop landscapes.

Question 23

How does water affect mass movement processes?

Answer 23

Water enhances mass movement processes and greatly increases the chances that mass
movement processes will occur by lowering the internal cohesion of most materials and
making the materials more susceptible to gravitational forces. In addition, water adds
weight to a slope, making the slope susceptible to failure

Question 24

Describe the significance of angle of repose.

Answer 24

The angle of repose is the steepest angle that unconsolidated materials may take before
sliding downslope. When slopes are steepened beyond their angle of repose, either by
natural or human actions, they may fail in mass movement events.

Question 25

How can forest fires and earthquakes influence mass movements?

Answer 25

Forest fires can eliminate plants that act to anchor soils, thereby promoting mass movement
events. In addition, fires can “bake” the ground, creating a water repellant layer at a
shallow depth that may increase surface runoff and initiate mud and debris flows. An
earthquake or its aftershocks can dislodge enormous volumes of rock and unconsolidated
material that move downslope under the influence of gravity as a mass movement event. In
addition, intense ground shaking during earthquakes can cause water-saturated surface
materials to lose their strength and behave as fluid-like masses that flow (liquefaction).

Question 26

What terms are used to classify mass movements by the type of motion they exhibit?

Answer 26

The terms used to describe mass movements by the motion type are: fall, slide, and flow

Question 27

Both slumps and rockslides move by sliding. How do these processes differ from one
another?

Answer 27

Rockslides occur when blocks of bedrock break loose and slide down a slope along a
relatively flat surface with little or no rotation or backward tilting. Slumps are the
downward sliding of a mass of rock or unconsolidated material along a curved surface.

Question 28

What factors contributes to the massive rockslide at Gros Ventre, Wyoming?

Answer 28

The Gros Ventre, Wyoming rockslide was triggered by heavy rains and melting snow. Here,
a great mass of sandstone, shale, and soil moved along a saturated clay bed, carrying the
debris and forest cover down a valley in a very short time period. An additional
contributing factor was that the sedimentary strata dipped 15 to 25 degrees in the same
direction as the slope.

Question 29

How is a lahar different from a debris flow that might occur in southern California?

Answer 29

Lahars occur when unstable layers of ash and debris become saturated with water and flow
down steep volcanic slopes. Debris flows in southern California differ from lahars in that
they are characterized by the rapid movement of large quantities of soil and regolith down
a steep slope, rather than volcanic material on volcanic slopes.

Question 30

Contrast earthflows and debris flows.

Answer 30

Earthflows are different from debris flows in that they are often more viscous, and thus
move slower. Debris flows often contain a greater proportion of water and a greater mix of
materials, whereas earthflows contain less water, and are primarily finer grained materials

Question 31

Describe the basic mechanisms that contribute to creep.

Answer 31

Creep occurs when soil and regolith move gradually downhill. Alternating expansion
and contraction of surface materials contributes to creep, such as freeze-thaw cycles, or
wetting and drying of surface materials.