Weathering

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Weathering

• You need your spiral. We will be meeting in the
  Library tomorrow.

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Why do we care about rocks?

• We can always take pointers from earth on how to
  be sustainable.
• Rocks make soil
• Why is soil important?
• Organisms, mainly microorganisms, inhabit the
  soil depend on it for shelter, food water.
• Plants anchor themselves into the soil, and get
  their nutrients and water. Terrestrial plants
  could not survive without soil, therefore, humans
  could not exist without soil either.

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Parent Material
Soil Formation

• The rock that has slowly broken down into smaller
  particles by biological, chemical, and physical
  weathering.
• To form 2.5 cm (1 in.) it may take from 200-1000
  years.

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• Mechanical Weathering no change in chemical
  composition--just disintegration into smaller
  pieces

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Mechanical Weathering
Exfoliation Rock breaks apart in layers that are
parallel to the earth's surface as rock is
uncovered, it expands (due to the lower confining
pressure) resulting in exfoliation.
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Sheet Joints(Exfoliation)
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Half Dome, Yosemite, CA
Stone Mountain, GA
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Exfoliated Domes, Yosemite
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Stone Mountain, Georgia, showing the product of
exfoliation due to unloading
Stone Mountain, GA
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Frost Wedging rock breakdown caused by expansion
of ice in cracks and joints
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Shattered rocks are common in cold and alpine
environments where repeated freeze-thaw cycles
gradually pry rocks apart.
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Weathering
Thermal expansion due to the extreme range of
temperatures can shatter rocks in desert
environments. Repeated swelling and shrinking of
minerals with different expansion rates will also
shatter rocks.
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Agents

• Water
• Wind
• Geological processes

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Role of Physical Weathering

• Reduces rock material to smaller fragments that
  are easier to transport
• 2) Increases the exposed surface area of rock,
  making it more vulnerable to further physical and
  chemical weathering

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Surface Area and Weathering
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Chemical Weathering

• A plants roots or animal cells undergo cell
  respiration and the CO2 produced diffuses into
  soil, reacts with H2O forms carbonic acid
  (H2CO3). This eats parts of the rock away.
  CHANGES THE COMPOSITION

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Olivine/pyroxene to clay
H2CO3 (acid)
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Feldspars to clay
H2CO3 (acid)
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Quartz to quartz (!)
anything
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This photo of Lime Sink was taken on 20 July
1932, over a week after the drawdown, which
occurred over the night of 9-10 July.
Karst landforms develop in areas underlain with
limestone
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Five main factors that affect the rate of
weathering.

• Climate Soil forms faster in warm, wet climates,
  because heat and moisture speed most physical,
  chemical and biological processes.
• Organisms Plants and decomposers add organic
  matter to soil over time
• Topography Hills and valleys affect exposure to
  sun, wind and water and they influence how soil
  moves (erosion)
• Parent materials Its attributes influence
  properties of the resulting soil.
• Time soil formation can take decades, centuries
  or millennia.

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