EARTH SCIENCE
CHAPTER 7
WEATHERING
EROSION
SOIL FORMATION
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7.1 Weathering
• What is it?
• 2 types
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• Mechanical (physical)—rocks are broken
down into smaller pieces
– Gravity—
– Temperature—
Ex: frost wedging
– Pressure-Ex: exfoliation
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• Review Definitions:
– Weathering—rocks at Earth’s surface are broken
down and changed
– Erosion—
– Deposition—
– SO? All of these processes have been going on
since Earth began!
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Green?
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• Chemical weathering—
– Hydrolysis—
• EX: decomposition of silicates
– Oxidation—
• EX: rust
– Carbonic acid—
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– Acid rain—pH of rain < 5.6
acidic
neutral
basic
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What can affect rates of weathering?
• Climate—
– Chemical—
– Mechanical—
• Type of rock—
• Surface area—
• Topography—erosion in areas of high relief
(steep) w/ deposition in areas of low relief
(flat)
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7.2 Erosion and Deposition
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Agents of erosion
• Gravity—
• Running water—
– Rivers, streams, water falls
• Glaciers—
• Wind—
• Plants and animals (biological)—
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GRAVITY EROSION
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RUNNING WATER EROSION
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GLACIAL EROSION
WIND EROSION
PLANT EROSION
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1930’S DUST BOWL CAUSED BY EROSION
OF TOPSOIL DUE TO EXTENSIVE
OVERFARMING AND DROUGHT
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• A word about beaches….
– Ocean waves are
constantly rebuilding and
shaping coastlines
– Sandbars can become
barrier islands but they
are not permanent!
– Barrier islands threatened
by hurricanes and beach
erosion and rising sea
levels
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Soil formation
• What is soil?
– Loose
– Formed by chemical, mechanical and biological
activity over very long periods of time
– Humus—
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• Soil Texture:
– Sand—
– Silt—
– Clay—
SO? The texture of a soil affects its capacity to
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Soil profile
• A vertical sequence of soil layers
• Residual soil—
• Transported soil—
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