Landform Geography Lecture 4

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Landform GeographyLecture 4
Weathering
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Weathering

• Process by which rocks break down into smaller
  pieces
• Two Primary Types
• Mechanical (or physical) cold, dry environments
• Chemical warm, moist environments

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Weathering Environments
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Mechanical Weathering

• Destruction of rock through physical stresses
• Rocks break into small pieces surface area of
  rock increases even greater weathering
• Types
• Frost Wedging
• Impact of Roots
• Temperature Fluctuations
• Salt Crystal Growth
• Exfoliation

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Frost Wedging

• Most common form of mechanical weathering
• Water flows into joints (fractures) in rock
• Expands 9 when it freezes
• Stress cracks rock

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Impact of Roots

• Roots or trunks of vegetation, especially trees,
  can grow through expand cracks in rocks

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Temperature Fluctuations

• Warming cooling rocks expand contract
  rocks break down especially in arid regions

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Salt Crystal Growth

• Salt in rocks weakens mineral bonds, loosening
  sediments which erode through wind or water

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Exfoliation

• Deep rock slowly uncovered by erosion of
  overlying layers pressure on rock reduced
• Under less pressure, rock layers flake off
• Most common in igneous or metamorphic rock

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Chemical Weathering

• Changes rock by altering its chemical composition
  water particularly important
• Types
• Hydrolysis
• Oxidation
• Carbonation
• Acid Rain

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Hydrolysis

• Hydrolysis literally means reaction with water.
• It is a chemical process in which a molecule is
  cleaved into two parts by the addition of a
  molecule of water.
• Decomposes silicate minerals in rocks
• Hydrogen hydroxyl ions from water added to rock
  silicate molecules split
• Rounds sharp edges and corners of rocks

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Hydrolysis
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Oxidation

• The combination of a substance with oxygen.
• Oxygen is added to chemical compounds, causing
  electrons in compounds to be lost
• Happens in rocks high in iron (rust)

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Carbonation

• Carbonation occurs when carbon dioxide is
  dissolved in water or an aqueous solution.
• CO2 dissolves in atmospheric water vapor, forming
  carbonic acid in precipitation
• This carbonic acid dissolves minerals, esp.
  limestone (calcium carbonate)

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Acid Rain
Weathering

• Coal-burning power plants in Midwest emit sulfur
  dioxide (SO2) nitrogen oxides (NOx)
• SO2 NOx mix with water in clouds to form
  sulfuric or nitric acid
• Clouds move east where acid rain falls
• Acid rain accelerates chemical weathering
• Acid rain can also harm lakes forests
• Regulation has cut acid emissions dramatically

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Effects of Acid Rain

• The ecological effects of acid rain are most
  clearly seen in the aquatic, or water,
  environments, such as streams, lakes, and
  marshes.
• Most lakes and streams have a pH between 6 and 8,
  although some lakes are naturally acidic even
  without the effects of acid rain.
• Buffering capacity
• Nitrogen is an important factor in causing
  eutrophication (oxygen depletion) of water
  bodies.