Weathering, Erosion, and Mass Wasting

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Weathering, Erosion, and Mass Wasting
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Earths external processes

• Weathering the physical breakdown
  (disintegration) and chemical alteration
  (decomposition) or rock at or near Earths surface

Bryce Canyon, UT
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Earths external processes

• Mass wasting the transfer of rock and soil
  downslope under the influence of gravity

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Earths external/surfical processes

• Erosion the physical removal of material by
  mobile agents such as water, wind, ice, or
  gravity

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Weathering

• Two types of weathering
• Mechanical weathering breaking of rocks into
  smaller pieces
• Four types of mechanical weathering
• Frost wedging alternate freezing and thawing of
  water in fractures and cracks promotes the
  disintegration of rocks

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Weathering

• Mechanical Weathering continued
• Unloading exfoliation of igneous and
  metamorphic rocks at the Earths surface due to a
  reduction in confining pressure
• Thermal expansion alternate expansion and
  contraction due to heating and cooling
• Biological activity disintegration resulting
  from plants and animals

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Weathering

• Chemical Weathering
• Breaks down rock components and internal
  structures of minerals
• Most important agent involved in chemical
  weathering is water (responsible for transport of
  ions and molecules involved in chemical processes)

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Weathering

• Major processes that control chemical weathering
• Dissolution
• Aided by small amounts of acid in the water
• Soluble ions are retained in the underground
  water supply
• Oxidation
• Any chemical reaction in which a compound or
  radical loses electrons

A granite in the early stages of chemical
weathering. Notice how it is getting pocked marks
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Weathering

• Major processes of chemical weathering
• Oxidation continued
• Important in decomposing ferromagnesian minerals
• When oxygen combines with another substances,
  oxidation has occurred.
• Sometimes a change in the color of a rock is an
  indication that oxidation has occurred.
• Rust on your car is from oxidation

red because of oxidation weathering
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Weathering

• Hydrolysis water
• Lots of it in Indiana
• The reaction of any substance with water
• Hydrogen ion attacks and replaces other positive
  ions (this is how caves form)

Karst sinkhole plain developed on limestone in
southern Indiana.Photo by Richard Fields
Diagram concept by R.L. Powell drafted by R.S.
Taylor
Karst in Indiana wanna go caiving!!!!! http//ig
s.indiana.edu/geology/karst/karstInIndiana/index.c
fm
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Products of Chemical Weathering
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Weathering

• Alterations caused by chemical weathering
• Decomposition of unstable minerals
• Generation or retention of materials that are
  stable
• Physical changes such as the rounding of corners
  or edges

Joshua Tree National Monument, California
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Weathering

• Rates of weathering
• Advanced mechanical weathering aids chemical
  weathering by increasing the surface area
• Others factors affecting weathering
• Rock characteristics
• Rocks containing calcite (marble and limestone)
  readily dissolve in weakly acidic solutions

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Increase in surface area by mechanical
weathering
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Weathering

• Others factors affecting weathering
• Climate
• Temperature and moisture are the most crucial
  factors (how much precipitation is there?)
• Chemical weathering is most effective in areas of
  warm, moist climates
• Topography (it depends. This is somewhat complex)
• Starting Material gt what kind of rock? Iron rich
  quick, silica rich slow

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Highest chemical weathering
Amazon Basin
climate
rain
South Pole
Also low Sierra Desert
Lowest chemical weathering
Temp
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Weathering

• Differential weathering
• Masses of rock do not weather uniformly due to
  regional and local factors
• Results in many unusual and spectacular rock
  formations and landforms

The Grand Canyon
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Differential weathering controlled by jointing
patterns