1.2%20Understanding%20How%20Weathering%20Wears%20down%20the%20Land

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1.2 Understanding How Weathering Wears down the
Land
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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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Weathering

• There are two types of weathering
• 1. Physical
• 2. Chemical

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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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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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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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1.2.1 1.2.2 Physical Weathering

• 3. Plant Growth / Root Wedging Expansion due to
  root growth.

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1.2.1 1.2.2 Physical Weathering

• 4. Exfoliation As pressure is released from
  certain rocks, it can cause layers to split and
  fall off.

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1.2.1 1.2.2 Physical Weathering

• 5. Animal Activity Animals tunnel into soil
  introducing water, air, etc.

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1.2.2 1.2.3. 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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• Chemical weathering involves three processes
• 1. The formation of solutions
• 2. Hydrolysis
• 3. Oxidation

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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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• 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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• 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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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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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)