Weathering,
Erosion, and Soil
What you need to learn
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How the process of weathering breaks down rocks
and how erosion transports weathered materials from one place to another
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How soil is formed and why soil is an important
natural resource
Weathering
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Process by which rocks on or near Earth’s
surface break down and change
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The movement of material is called erosion
Mechanical Weathering
l Process by which rocks and minerals break down into
smaller pieces
l Also called physical weathering
l Factors involved:
¡ Temperature – freezing and thawing
l Frost wedging
¡ Pressure – reduction of pressure or increase of
pressure
l Exfoliation: removing of rock layers
Chemical Weathering
l Process in which rocks undergo chemical change
l Often involve water (hydrolysis), oxygen (oxidation),
carbon dioxide, and acids
l Temperature influences the rate
What else can effect the rate?
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Climate: warm temperatures, abundant rainfall,
and lush vegetation increase the rate
l
Cool, dry climates can also have abundant
weathering
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Rock type and composition
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Surface area
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Topography and other variables
Erosion and Deposition
l The final stage of erosion is deposition
l Gravity is a major factor
l Running water can move large particles
¡ Rill erosion: running water in small channels on sides
slopes
¡ Gully erosion: enlarged channels
l Coastal deposition and erosion
l Glacial erosion
l Wind erosion
l Erosion by plants, animals, and humans
Formation of Soils
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Soil is found almost everywhere on Earth
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Soil is loose rock particles and decaying
organic material (humus) overlaying the bedrock
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There are a large variety of different types of
soils
Soil Composition
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Residual soil: found above the parent material
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Transported soil: moved from parent material to
another location
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It can take hundreds of years for the formation
of only 1cm of soil to form
Soil Profiles
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Vertical sequence of soil layers
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Soil horizon: distinct layer or zone within the
profile
¡Horizon A:
lots of organic matter and humus
¡Horizon B:
found under A and contain subsoils
¡Horizon C:
below B, contains weathered parent rock
Types of Soils
Other features of soils
lTexture
lFertility
lColor