Transcript of Chapter 5.1. What is Weathering? Weathering can be defined as any chemical or mechanical process by...
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- Chapter 5.1
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- What is Weathering? Weathering can be defined as any chemical
or mechanical process by which rocks exposed to weather undergo
changes in character or are broken down into smaller pieces.
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- Mechanical Weathering Mechanical Weathering is a type of
weathering that breaks down rocks into smaller pieces without
changing the chemical composition of the rock. For example, Granite
can be broken down into smaller pieces, but the smaller pieces are
still Granite.
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- Agents of Mechanical Weathering Frost Wedging When water
freezes in the cracks of rocks causing them to expand and break the
rock. The products of frost wedging are large piles of rocks called
talus.
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- Frost Wedging Talus produced by Frost Wedging
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- Agents of Mechanical Weathering Unloading and Exfoliation When
large sections of rock buried underneath the ground are exposed at
the surface, enormous amounts of pressure are released. This
release of pressure is referred to as unloading. After unloading,
the rocks begin to flake off in sections like an onion. This is
referred to as exfoliation.
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- Unloading and Exfoliation Giant Slabs of rock flake off As a
result of Unloading and Exfoliation
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- Agents of Mechanical Weathering Biologic Activity Weathering
that occurs as a result of the actions of living organisms like
plants and animals. Plants often cause mechanical weathering when
their roots penetrate down into the cracks of rocks. When the roots
grow they expand. Animals burrowing into the ground can also create
cracks in the rocks.
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- Biologic Activity Roots penetrating the cracks in rocks Gophers
and Earthworms Burrowing Also contribute to Mechanical
Weathering
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- Chemical Weathering When rocks that weather change their
composition into a new type of rock, this is referred to as
chemical weathering. For example, if limestone (calcite) dissolves
as a result of acid rain, then it becomes carbon dioxide gas and
various ions.
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- Chemical Weathering The three main types of chemical
weathering. Carbonation occurs when carbonic acid (H 2 CO 3 )
dissolves minerals in rocks. Hydrolysis occurs when hydrogen in
water dissolves minerals in rocks. Oxidation occurs when oxygen
reacts with minerals in rocks.
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- Chemical Weathering Examples of each type include. Carbonation
occurs when acid rain (carbonic acid) dissolves limestone bedrock
to produce caves. Hydrolysis transforms feldspar (in granite), to
produce clay sediments. Oxidation transforms rocks with iron (like
basalt and gabbro) into hematite (rust).
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- Chemical Weathering Oxidation of Mafic/Basaltic Rocks To
produce the mineral Hematite Weathering of Granite to Produce clay
sediments Carbonic Acid dissolves limestone To produce caverns
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- Rate of Weathering The most important factors that affect the
rate (time) of weathering are Surface Area - More cracks means more
surface area, more surface area means more weathering. Composition
Certain minerals are more resistant to weathering than others.
Quartz for example is more resistant to weathering than
calcite.
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- Rate of Weathering How Weathering Affects the Surface Area and
the Rate of Weathering
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- Rate of Weathering Climate Hot, humid climates have a fast rate
of weathering. Cold, dry climates have a slow rate of weathering.
Vegetation Places with more vegetation tend to have a higher rate
of weathering because certain plants help produce acids that help
speed up the rate of weathering.
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- Rate of Weathering Varies depending upon the Climate