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EXFOLIATION – PEELING
AWAY OF ROCK
due to
unloading
(reduced
pressure at
earth’s surface)
or fluctuations
in temperature.
Rocks expand
and crack
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Physical (Mechanical) Weathering
• Abrasion
• Caused by rocks colliding against each
other
• Agents that move rock include
• Wind
• Liquid water (streams, rivers)
• Solid water (glaciers)
• Gravity alone (along a cliff face)
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PHYSICAL WEATHERING -
ABRASION
SCRAPE, GRIND AND WEAR AWAY
ROCK DURING EROSION
WATER WIND
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Physical (Mechanical) Weathering
• Plants and animals are also important
agents of physical weathering
(Biological)
• Expanding seeds and growing roots push
outward with tremendous force
• Soil burrowing creatures abrade small
rock particles
• earthworms are especially important
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PHYSICAL WEATHERING –
ROOT ACTION
PLANT ROOTS UPLIFT AND
FRACTURE ROCK
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Chemical Weathering
1. Hydration
• The breakdown of rock due to a chemical
change in the rock. Examples:
Feldspar Clay
Fe (iron) + O2 Fe3O3 (iron oxide,
commonly called rust)
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CHEMICAL WEATHERING
HYDRATION
• OCCURS WHEN Water combines with
minerals – most often in granite (mica and
feldspars) to form CLAY
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2.Carbonation
Example 1 Carbon Dioxide
• Carbon dioxide mixes with water and
produces Carbonic Acid (a weak acid).
CO2 + H2O H2CO3
• Carbonic acid will slowly dissolve rocks
and minerals.
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Example of carbonation
• Limestone is a hard rock that is weathered
by weak acids
H2O + CO2 Carbonic acid H2CO3
This is how most caves are formed
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CARBONATION
Water containing carbonic acid dissolves
minerals (all rain water is slightly acidic)
Most strongly affected are calcite minerals:
limestone and marble
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3. Man Made Acids
Nitric and sulfuric acids
• produced by industrial
processes and cause
the chemical
weathering of
buildings, statues,
headstones and other
structures
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5. Oxidation
• Oxygen is added to other elements
• Rusting of magnetite into hematite
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EXAMPLES OF CHEMICAL
WEATHERING
OXIDATION OCCURS when free oxygen
combines chemically with metallic elements
(usually iron)
AKA RUST
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Chemical Weathering Rates
Climate
• Chemical reactions occur faster at higher
temperatures and often require water (H2O)
At what latitudes does chemical
weathering occur at the greatest rate?
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Climate vs. Weathering rates
Average Annual Temperature
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Chemical Weathering Rates
Rock Type
• Some minerals are resistant to
chemical weathering
• Ex. quartz
• that’s why most beach sand is made of
quartz
• Some minerals are easily weathered
chemically
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Surface Area
• Greatly influences weathering rates
• weathering occurs at the surface of rock
particles
Increasing Surface Area
38.
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Question 41 from the most recent
Regents exam – August ‘07
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THE END PRODUCTS OF
WEATHERING
CALLED SEDIMENTS OR SOIL
SOIL: a combination of sediment, rock
minerals, and humus (organic material)
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SOIL – THE PRODUCT OF
WEATHERING
AFTER THOUSANDS OF YEARS…
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SOIL HORIZONS
Layers that develop as a result of the weathering
processes, biologic activity, and leaching (flow
of water through rocks)
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Soil Development
Size and thickness
of each horizon
depends on:
Climate
Vegetation
Slope (gradient or
incline)
Time
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2 TYPES OF SOIL
TRANSPORTED SOIL: SOIL CARRIED BY
EROSION AND DEPOSITED ON THE
BEDROCK (MOST SOIL IS TRANSPORTED)
RESIDUAL SOIL: SOIL FORMED BY THE
WEATHERING OF THE BEDROCK
DIRECTLY BENEATH IT
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WEATHERING SUMMARY
• WEATHERING IS THE BREAKDOWN OF
ROCK INTO SEDIMENTS
• PHYSICAL WEATHERING – INCREASES
SURFACE AREA - COLD/HUMID
CLIMATE
• CHEMICAL WEATHERING –
WARM/HUMID CLIMATE
• IN BOTH CASES, WATER IS THE
PRIMARY INGREDIENT
