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WEATHERING

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WEATHERING Powered By Docstoc
					             Onion skin
             weathering
Weathering is the physical, chemical and biological
breakdown of rocks in situ (same place).


Onion skin weathering is also known as:
•Exfoliation
•Thermal Expansion
•Insolation weathering
        Day clouds
The absence of Time in tropical deserts
 & the overhead sun produces high day
                        The sun’s heat
           time temperatures
                      causes the outer
                          layers of the
                       rock to expand

     Most common in fine-
         grained rocks
     (e.g. volcanic rocks)
          & boulders
 With no clouds      Repeated daily heating &
                      Night Time
 rocks cool quickly. cooling causes outer layers
 A process known as rock to be weathered
                     of                     Cooling causes
 radiation cooling                          the outer layers
Different minerals                           of the rock to
expand and contract                          contract
at different rates                                     Layers or
causing stresses                                   shells of rock
along mineral          Quarts increases in
                                                      peel away
boundaries.            size by three times
                       more than feldspar




       Layers of rock collect on the desert floor
        Onion skin weathering
• Exfoliation is caused by alternate expansion &
  contraction caused by temperature changes.
What happens in the day time?
(Dark rock can reach over 50oC)
What happens at night time?
• The outer layers of rock are exposed to extreme
  temperatures (no vegetation or soil). Outer layers
  of rock break away from the cooler inner layers.
Where can we find extreme temperature changes?

				
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posted:12/4/2011
language:English
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