Transcript Chapter 7 - River Ridge

Chapter 7- Weathering,
Erosion and Soil
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I. Weathering
A. The process by which rocks on
or near Earth’s surface break down
and change is called weathering.
1. Removal and transport of
weathered material from one
location to another is erosion
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2. The process by which rocks and
minerals break down into smaller
pieces is mechanical weatheringalso called physical weathering
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Physical weathering
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3. Mechanical weathering does
not involve any change in a rock’s
composition, only changes in the
size and sometimes the shape of
the rock.
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Mechanical weathering
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B. Factors that are involved in
mechanical weathering.
1. Temperature plays a big role in
mechanical weathering.
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2. Repeated thawing and freezing
of water in the cracks of rocks is
called frost wedging.
3. Frost wedging is responsible for
potholes.
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4. Pressure is
another factor.
Over time, layers
of rock are
stripped away is
called exfoliation.
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C. Chemical weathering is when
rocks and minerals undergo
changes in their composition as
the result of chemical reactions.
1. Some agents, water, oxygen,
carbon dioxide, and acids.
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2. Water can dissolve many kinds
of minerals and rocks. Water has
an active role in some reactions.
3. The reaction of water with
other substances is known as
hydrolysis
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4. Hydrolysis
occurs in the
decomposition of
silicate minerals.
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5. Oxygen can combine with other
substances oxygen and other
substances are called oxidation.
6. Acid rain also can chemically
change some minerals or rocks.
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D. Affects of rate of weathering.
1.
Natural weathering of earth
materials occurs very slowly.
2.
The climate of an area is a major
influence on the rate of chemical
weathering of earth materials.
(Temperature, precipitation)
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E. Rock type and composition
1.
Characteristics of rocks
including how hard or resistant
they are to being broken down
depend on their type and
composition.
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II. Erosion and Deposition
A. Materials that are dropped in
another location is the process of
deposition, the final stage of the erosion
process.
1. Gravity is associated with many
erosion agents because the force of
gravity tends to pull all materials down
slope.
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2. Erosion also occurs by running
water.
3. The erosion by running water in
small channels, on the side of a
slope is called rill erosion.
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4. Rills commonly form on a slope.
5. When channel becomes deep and
wide, it can evolve into gully erosion.
(These can be big troubles for farmers)
6. Erosion also occurs because of
costal depositions.
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Gully Erosion
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7. Glaciers also cause erosion
8.
Wind causes erosion.
9. Humans, plants and animals
cause erosion
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III. Soil Formation
A. Soil is almost everywhere on earth.
1.
Soil is the loose covering of broken
rock particles and decaying organic
matter, called humus, overlying the
bedrock of Earth’s surface.
2. Soil forms in layers
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2. The solid bedrock from which
weatherized pieces of rock first
break off is known as parent rock.
3. Soil located above its parent
material is called residual soil.
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4. Transported soil has been
moved to a location away from its
parent bedrock.
5. Things that cause this are
erosion, running water, wind and
glaciers.
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6. A soil profile is
the vertical
sequence of soil
layers.
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6. A distinct
layer, or zone
within a soil
profile is called
soil horizons.
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B. Soil Types
1.
The four major types of soil are
polar, temperate, desert and tropical.
2. Polar soils- form at high latitudes and
high elevations in places such as
Greenland, Canada, and Antarctica.
They have good drainage but no distinct
horizons.
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3. Temperate soils- varies greatly
and is able to support such diverse
environments as forests,
grasslands, and prairies.
Temperate zones have about 5060cm of water.
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4. Desert soils- receives low
amounts of precipitation. Less
than 25cm a year. Desert soils are
also light- colored, coarse, and
many contain salts and gypsum.
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5. Tropical soils- experience high
temperatures and heavy rainfall. Tend
to have infertile soil. Intense
weathering and bacterial activity leave
tropical soils with very little humus and
very few nutrients. The soil is red in
color as a result of oxidation of iron.
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C. Soil textures
1. Particles of soil are classified
according to size as being clay, silt
or sand with clay being the
smallest and sand being the
larges.
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D. Soil fertility
1.
Soil fertility is the measure of
how well a soil can support the
growth of plants. Factors that
affect soil fertility include the
available of minerals and nutrients
and the number of microorganism.
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E. Soil color
1. A soil’s composition and the climate
in which it develops are main factors
that determine the soil color.
2. Topsoil is usually dark-colored
because it is rich in humus.
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3. Color cannot predict fertility.
4. Red and yellow soils may be
the result of oxidation of iron and
minerals.
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5. Grayish or bluish soils are
common in poorly drained regions
where soils are constantly wet and
lack oxygen.
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THE END
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