Transcript Chapter 7- Weathering, Erosion and Soil

Chapter 7- Weathering,
Erosion and Soil
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I. Weathering
• Where rocks on or near Earth’s
surface break down and change is
called weathering.
• Removal and transport of
weathered material from one
location to another is erosion
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Two Types of Weathering
1. Mechanical or Physical
2. Chemical
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Mechanical Weathering
Where rocks and minerals break down
into smaller pieces.
The only thing that changes is the
rock’s size and shape.
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Cleopatra’s Needle in
NYC.
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2 Factors involved in mechanical
weathering:
1. Temperature
2. Pressure
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Temperature
• When water freezes, it expands and
increases in volume.
• Water collects in the cracks of rocks.
• It temperatures drop to freezing, it
expands and exerts pressure on the
rocks therefore causing them to split.
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This is called “Frost Wedging.”
The repeated thawing and freezing
of water in the cracks of rocks.
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Pressure
Rocks build up on
top of one
another causing
pressure. When
overlying rocks
are removed, the
pressure on the
bedrock below is
reduced.
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Pressure continued….
Over time, the outer
layers of rock are
stripped away in
succession, similar
to an onion being
peeled. This is
called
“exfoliation.”
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Chemical Weathering
• Where rocks and minerals undergo
changes in their composition as
the result of chemical reactions.
• Some agents include: water,
oxygen, carbon dioxide, and acids.
• Temperature is involved also.
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The Agent: Water
Water can dissolve many kinds of
minerals and rocks. Water has an
active role in some reactions.
The reaction of water with other
substances is known as
hydrolysis
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The Agent: Oxygen
Oxygen can combine with other
substances. This chemical reaction
of oxygen with other substances is
called oxidation.
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The Agent: Carbon Dioxide
This is produced by living organisms during
the process of respiration.
When carbon dioxide combines with water
in the atmosphere, it forms a weak carbonic
acid that falls to Earth’s surface as
precipitation.
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Limestone Cave in Guatemala produced when carbonic acid
Dissolved the calcite in the limestone rock.
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The agent: Acid Rain
Caused by the oxidation of sulfur dioxide
and nitrogen oxides that are released into
the atmosphere by human activities.
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What affects the rate of
weathering?
Occurs very slowly
1. The climate of an area is a major influence on
the rate of chemical weathering of earth
materials. (Temperature, precipitation, and
evaporation)
2. Rock type and composition
3. Surface Area
4. Topography
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Chemical weathering occurs…
In areas that are tropical! Warm, abundant
rainfall, lush vegetation.
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Mechanical or physical
weathering occurs…
In cool, dry climates. Where water freezes
and thaws repeatedly.
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7-2 Erosion and
Deposition
As you recall… erosion is the process that
transports Earth materials from one
place to another.
Rivers, running water in streams,
glaciers, wind, and ocean currents can
pick-up and carry materials.
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At some point though…
The movement of transported materials will
slow down.
When this happens, the materials are
dropped in another location in a process
called DEPOSITION (final stage of
erosional process).
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What can pick-up and carry
materials?
1. Gravity: Being pulled downhill
2. Running water moving downhill
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Rill Erosion
Erosion by running water in
small channels, on the side
of a slope.
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Gully Erosion occurs when:
•
Channels becomes deep and
wide. (These can cause big
trouble for farmers)
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Gully Erosion
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Water erosion
also includes:
Coastal deposition and
erosion. Current,
waves, and tides carve
out cliffs, arches, and
other features along the
continent’s edges.
Sand particles
accumulate on
shorelines and form
dunes and beaches.
Sandbars form as a
result of being picked
up and moved from the
shoreline.
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What else can pick-up and move
materials?
•Glaciers
•Wind
•Humans, plants and animals
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Glaciers
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Wind and planting a garden
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