Unit 4: Weathering, Erosion, Deposition and Landscapes

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Unit 4 Weathering, Erosion, Deposition and
Landscapes

• Weathering

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What is weathering?

• The breaking down of rock due to physical and/or
  chemical changes in the rock as it is exposed to
  the atmosphere
• Occurs at the interface between the atmosphere
  and the lithosphere
• Results in smaller pieces of rock called sediments

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Physical weathering

• Results in a change in appearance of rock (size,
  shape, state)
• Types include frost action, plant action,
  pressure unloading

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Frost action

• Occurs in a cold and moist climate
• Alternating freezing and melting of water in the
  rock cracks the rock

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Plant action

• Plant roots grow into small cracks in rock and
  widen them

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Pressure unloading

• Rock cracks when pressure over the rock is removed

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Chemical Weathering

• Results in a change in chemical composition of
  the rock
• Types include oxidation, acid reactions

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Oxidation

• Addition of oxygen to metalresults in rust (iron
  oxide)

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Hydrolysis

• Chemical weathering by reaction of water with
  other substances
• When certain minerals are exposed to water they
  dissolve into ionsex feldspar
• Feldspar will chemically weather into clay
  (kaolinite)
• Water will help any chemical reaction

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Acids

• Gases such as sulfur dioxide, nitrogen dioxide,
  carbon dioxide will dissolve in rainwater forming
  acid rain (sulfuric acid, nitric acid, and
  carbonic acid -a weak acid)
• Calcite will dissolve completely in carbonic
  acid-thus chemically weather any rock containing
  this mineral easily
• Acid rain which forms naturally, for example
  volcanic activity, or by pollutants, harms any
  exposed rock, buildings and monuments

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End RESULT of Weathering

• SEDIMENTS!
• INCLUDES-CLAY, SILT, SAND, PEBBLES AND COBBLES
• SEE ESRT P6,7

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What can affect the rate of weathering?

• Size of the sediment
• Type of mineral (hardness)
• Temperature
• Humidity (amount of moisture present)