Classroom presentations to accompany Understanding Earth, 3rd edition

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Classroom presentations to accompany
Understanding Earth, 3rd edition

• prepared by
• Peter Copeland and William Dupré
• University of Houston

Chapter 6 Weathering and Erosion
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Weathering and Erosion
Tim Davis/Photo Researchers
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Weathering

• Physical and chemical changes that occur in
  sediments and rocks when they are exposed to the
  atmosphere and biosphere.
• Not the same as erosion.

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Factors Controlling Rates of Weathering
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Chemical weathering

• This process occurs because minerals formed deep
  in the earths interior are not stable under
  surface conditions.
• Stability is generally the reverse of Bowens
  reaction series.
• The principle agent of chemical weathering is
  water.

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Chemical weathering of silicates

• Quartz very stable
• Feldspars form clay minerals
• Mafic minerals decompose to oxides

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Chemical weathering of carbonates

• Easily soluble in water (especially with some
  acid present)
• Ca and Mg taken into solution

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Weathering rates of gravestones
Marble
Slate
Fig. 6.1
R. Siever
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Etched and corroded feldspar in the soil zone
Fig. 6.2
Berner Holden, 1977
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Fig. 6.3a
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Fig. 6.3b
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Fig. 6.3c
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Analogy of weathering making coffee
fresh grounds water coffee residue
(a
solution) K-feldspar water K kaolinite
(a clay
mineral)
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Weathering and Making coffee
Fig. 6.4
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Weathering by solution

• The complete breakup of minerals into
• ions in solution
• NaCl (halite) is the best example, but is
• geologically unimportant
• calcite (limestone) CaCO3
• CaCO3 H2CO3 Ca2 2HCO3-
• Mafic silicates dissolve much more
• slowly

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Mechanical Weathering Changes the Surface to
Volume Ratio
Fig. 6.5
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Fig. 6.6
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Fig. 6.6
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CO2 and the Atmosphere, Weathering, and the
Climate
Fig. 6.7
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Fig. 6.8
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Weathering Oxides Provide Color to the Desert
Landscape
Betty Crowell
Fig. 6.9
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Weathered Limestone
Fig. 6.10
Ric Ergenbright
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(No Transcript)
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Joint-controlled Weathering
Fig. 6.11
Jeff Foott/DRK
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Mechanical weathering

• Frost water expands by 9 when it freezes
• Thermal expansion differential thermal
  expansion of minerals creates stress in rocks
• Organic activity tree roots to
  micro-organisms
• Mechanical abrasion things go bump

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Role of Organisms in Weathering
Fig. 6.12
Peter Kresam
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Gneiss Boulder Fractured by Frost Action
Michael Hambrey
Fig. 6.13
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Exfoliation Dome in Yosemite
Fig. 6.14
Tony Waltham
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Spheroidal Weathering
Fig. 6.15
Michael Follo
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Weathering terms

• Bedrock unaltered rock of any kind
• Regolith a layer of broken pieces of rock
  and slightly altered rock that overlies the
  bedrock
• Soil a layer of altered mineral material
  usually mixed with organic material

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Weathering, Soil Formation, and Erosion
Fig. 6.16
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Weathering, Soil Formation, and Erosion
Fig. 6.16
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Change in U.S. soil erosion rates
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Soil Profile
Fig. 6.17
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Laterite
Fig. 6.18a
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Pedalfer
Fig. 6.18b
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Pedocal
Fig. 6.18c
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Sand
Fig. 6.19
Rex Elliot