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Chapters 4 & 5
Weathering and Erosion
Weathering
• Weathering is the
breaking down of rocks
and other materials
• 2 types of weathering
– Mechanical
– Chemical
Mechanical/Physical
Weathering
• Mechanical Weathering
occurs when rocks are
broken down into smaller
pieces, but the chemical
composition is not
changed
• Examples: temperature,
frost, tree roots, gravity
(abrasion)
Physical Weathering
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Mechanical Weathering
• Temperature - rocks expand when they are
heated up, and contract when they are cooled.
This process breaks rock.
• Frost Action- water gets into cracks of rock
and freezes when it gets cold. Crack expands
• Organic Activity - roots of trees break rocks
• Gravity - rocks are pulled downward by gravity
• Abrasion - wind blown sand wears away rocks
(also water running over rocks)
Chemical Weathering
• Chemical weathering
occurs when rocks are
broken down and their
chemical composition is
changed
• Examples: water, carbon
dioxide, oxygen, plants
Chemical Weathering
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Chemical Weathering
• Water - most chemical weathering occurs w/
water/CO2. Water dissolves minerals.
• Oxidation - process in which oxygen chemically
combines with another substance. (iron in rocks
can rust)
• Carbonation - occurs when CO2 dissolves in
water and forms carbonic acid.
• Plant Acids - moss and lichens produce weak
acids that dissolve minerals in rocks
Soil Formation
• Soil is formed when rocks are continuously broken down
by weathering.
• Soil that stay close is called residual, soil that is moved
is called transported.
• Bedrock is the layer of rock beneath the soil
Erosion
• Erosion is the process by
which weathered rock is
moved.
• Grand Canyon was formed
by erosion.
• Causes of erosion: gravity,
wind, running water,
glaciers, and waves.
• Deposition is the process
by which sediments are laid
down in a new place.
Erosion
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Erosion
• Gravity pulls rocks and soil down slopes.
Examples: landslide or mudflow
• Wind is most active agent of erosion in deserts
and on beaches. Wind erosion can form dunes
or caves.
• Running water is the major cause of erosion.
Examples: rivers, streams, and runoff.
• Glaciers ice erodes rocks beneath it by
abrasion.
• Waves erode and shape shorelines.
Erosion Caused by Wind
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Humans Impact Erosion
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