1. 1.2 Understanding How Weathering Wears down the Land
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2. 1.2.1 . What is the Difference between Physical and Chemical Weathering?
“Weathering” is the breakdown of rocks, soil and minerals through contact with the earth.
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3. Weathering There are two types of weathering: 1. Physical 2. Chemical
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4. 1.2.1 – 1.2.2 Mechanical Processes by which Physical Weathering Occurs
Physical Weathering: Is the breakdown of rock and minerals by mechanical stress. There are many examples…
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5. 1.2.1 – 1.2.2 Physical Weathering: Mechanical Processes
1. Frost Fracture: The expansion of freezing water that causes rocks to crack.
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6. 1.2.1 – 1.2.2 Physical Weathering: Mechanical Processes
2. Heat Expansion: When heated, rocks can expand and subsequently fracture.
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7. 1.2.1 – Physical Weathering
3. Plant Growth / Root Wedging: Expansion due to root growth.
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8. 1.2.1 – Physical Weathering
4. Exfoliation: As pressure is released from certain rocks, it can cause layers to split and fall off.
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9. 1.2.1 – Physical Weathering
5. Animal Activity: Animals tunnel into soil introducing water, air, etc.
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10. 1.2.2 & Chemical Weathering
Chemical weathering: This is the breakdown of rocks and minerals by chemical reactions. It usually involves the action of rainwater.
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11. Chemical weathering involves three processes:
1. The formation of solutions
2. Hydrolysis
3. Oxidation
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12. 1.2.2 & 1.2.3. Chemical Weathering The formation of various solutions:
A. Often rainwater absorbs chemicals from the atmosphere, along with acids from the soil
B. Chemicals react with rock and minerals, causing particles some to dissolve and move away
C. Produces acids
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13. Hydrolysis: A. Breaking of bonds using water (hydro)
B. Carbonic acid reacts with silicates in some rocks
C. Produces a soft clay, from which potassium, sodium and magnesium are subsequently leached.
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14. A. The reaction of metallic minerals to oxygen.
Oxidation:
A. The reaction of metallic minerals to oxygen.
B. Produces oxides, which tend to be softer than the original mineral. i.e. rust (red on iron & green on copper).
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15. 1.2.4. Environmental Conditions & Rate of Physical & Chemical Weathering
Key Ideas!
Physical weathering is increased in moist regions with a wide temperature range
Chemical weathering is increased in hot, moist regions
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16. 1. 2. 4. Environmental Conditions & Rate of Physical &
1.2.4 Environmental Conditions & Rate of Physical & Chemical Weathering
Enviro. Condition Physical Rate Chemical Rate
Heavy rain Increases rate Increase rate
Varying temp Increase (frz/thaw) Cold temps slow rate
High temperature Increases Increases
Ocean waves Increase (abrasion) Increases (salt water)
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