Weathering

1
Weathering
http//amazingworld.5u.com/photo.html
2
Objectives

• Define weathering
• Identify causes of weathering
• Physical or Mechanical Weathering
• Chemical Weathering
• Biological Weathering
• Discuss soil formation

3
Weathering

• Weathering is a set of physical, chemical, and
  biological processes that alter the physical and
  chemical state of rocks and soil at or near the
  earth's surface.

http//www.uh.edu/jbutler/physical/chapter6.html
4
Effects of Weathering

• Loss of atoms and molecules from weathered
  surfaces.
• Addition of specific atoms to the weathered
  surface.
• Breakdown of one mass into two or more masses.

5
Chemical Weathering

• Involves the alteration of the chemical
  composition of weathered material.
• There are different process that result in
  chemical weathering including
• Hydrolysis
• Oxidation
• Carbonation

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Hydrolysis

• Chemical weathering is a process that involves
  the reaction
• between mineral ions and the ions of water (OH-
  and H),
• and results in the decomposition of the rock
  surface
• by forming new compounds, and by increasing the
  pH of the
• solution through the release of the hydroxide
  ions.
• - Silicate minerals weather by hydrolysis to form
  clay.

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Oxidation

• Chemical attachment of free oxygen to other
• elements and compounds.
• Iron-bearing silicate minerals that
• undergo oxidation include the
• following
• pyroxene
• amphibole
• biotite
• olivine
• Rocks that contain these elements weather by
  oxidation into
• an orange color.

http//wwwrses.anu.edu.au/research/annrep/ar2006/e
e/index.php?ppillans
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Carbonation

• Dissolving of calcium
• carbonate (limestone) in
• acidic groundwater
• - similar to hydrolysis but all the products are
  ionic and there is no residue
• - produces bicarbonate (HCO3), a major part of
  the dissolved load of most rivers
• - the carbonation of limestone results in karst
  topography caves, sinkholes, etc.

http//www.khaolaklanddiscovery.com/_images/tours/
khao_sok/old_coral_big.jpg
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Physical Weathering

• Breakdown of mineral or rock material by entirely
  mechanical methods brought about a variety of
  reasons.
• Frost Wedging
• Exfoliation or Unloading
• Thermal Expansion
• Plant Wedging

http//members.aol.com/rhaberlin/mwstyg.htm
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Frost Wedging

• Mechanical disintegration, splitting or break up
  of rock by the pressure of water freezing in
  cracks, crevices, pores, etc.
• Caused by repeated freeze-thaw cycle of water in
  extreme climates.

http//regentsprep.org/Regents/earthsci/units/weat
hering/frostwedging.gif
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Exfoliation or Unloading

• Expansion of rock caused by lifting and erosion
• Rock breaks off into sheets along joints that
  parallel surface.

http//facstaff.gpc.edu/pgore/EarthSpace/condest
r.html
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Thermal Expansion

• Repeated cooling and heating of rock.
• Heat caused rock to expand and cooling causes
  rock to contract
• Looks very similar to frost wedging and salt
  crystal growth, but typically occurs in climates
  of extreme weather changes.

Thermal shattering of sandstone by forest fire.
http//w3.salemstate.edu/lhanson/gls210/gls210_we
ath1.htm
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Plant Wedging

• Plant roots can wedge into cracks in rocks and
  produce enough pressure to split them
• Chemicals produced by the roots of plants help
  in the chemical weathering, as enzymatic activity
  digest the rock as the plant searches for
  nutrients in the rock.

http//facstaff.gpc.edu/pgore/EarthSpace/condest
r.html
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Biological Weathering

• Animals and Plants can assist in breaking down
  rocks into sediment and soil.
• Biological Weathering can be
• caused by
• Roots of trees and other plants
• Lichens, fungi, and other microorganisms.
• animals

http//w3.salemstate.edu/lhanson/gls210/gls210_w
eath1.htm
15
Soil Formation

• Soil is formed from the weathering of rocks and
  minerals.
• Surface rock breaks down by weathering and is
  mixed with organic material. Over time it creates
  a thin layer of soil.

lh3.google.com/.../s800/IMG_1466-1.jpg
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Five Soil Forming Factors

1. Parent Material- The primary material from which
   rock is formed.
2. Climate- Weathering forces including heat, rain,
   ice snow, wind, etc.
3. Organism- all animals living in or on the soil.
   Ex Animals living in the soil will affect how
   soil is moved around and decomposition of waste
   materials.
4. Topography- the location of the soil on a
   landscape. Ex Soil at the bottom of a hill will
   get more water than that on the slope.
5. Time- The formation of soil takes years.

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Topography
Image courtesy of the United States Department of
Agriculture, Soil Conservation
Service http//soil.gsfc.nasa.gov/soilform/parmat.
htm
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References

• http//uregina.ca/sauchyn/geog221/wthrng.html
• http//www.physicalgeography.net/fundamentals/10r.
  html
• http//gpc.edu/pgore/EarthSpace/condestr.html
• http//geosun.sjsu.edu/paula/134/pdf/lecture3.pdf
• http//library.thinkquest.org/J003195F/soil.htm
• http//soil.gsfc.nasa.gov/soilform/parmat.htm
• http//w3.salemstate.edu/lhanson/gls210/gls210_we
  ath1.htm