Test 2 Chapter 8 Flashcards
List examples of Earth’s internal and external processes.
External processes include weathering, mass wasting, and erosion. Internal processes
include mountain building, volcanic activity.
From where do internal and external processes derive their energy?
External processes derive their energy from the Sun, while internal processes derive their
energy from Earth’s interior.
Contrast mechanical and chemical weathering.
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
When a rock is mechanically weathered, how does its surface area change? How does this
influence chemical weathering?
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.
How is carbonic acid formed in nature? What products result when carbonic acid reacts
with potassium feldspar?
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.
Distinguish between four types of mechanical weathering.
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.
Explain how angular masses of rock often become spherical boulders.
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.
List three or more factors that influence the type and rate of weathering.
Factors that influence the type and rate of weathering include: rock characteristics,
climate, and human activities.
Explain why soil is considered to be an interface in the Earth system.
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.
How is regolith different from soil?
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.
Why is texture an important soil property?
Texture is an important soil property because it strongly influences the soil’s ability to
retain and transmit both water and air.
List the five basic controls of soil formation.
The five controls of soil formation are parent material, climate, plants and animals,
topography, and time.
Which factor is most influential in soil formation?
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.
How might the direction a slope is facing influence soil formation?
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.
Describe the following features or processes: eluviation, leaching, zone of accumulation,
and hardpan.
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.
Why are soils classified?
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.
What are three particularly extensive soil orders in the 48 United States? What are two soil
orders in Alaska?
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.
Link these phenomena in a description of soil erosion: sheet erosion, gullies, raindrop
impact, rills, and streams.
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.
How have human activities affected the rate of soil erosion?
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.
Briefly describe three methods of controlling soil erosion
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.
What force is responsible for mass movement?
Gravity is the force responsible for mass movement.
Describe the role of mass movement in landscape development.
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.
How does water affect mass movement processes?
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
Describe the significance of angle of repose.
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.
