Aim: What factors determine the rate of weathering

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Aim What factors determine the rate of
weathering?
I. Rate of weathering factors
A. Rock composition
1. Igneous and metamorphic rocks do not weather
easily
2. Rocks containing the mineral quartz do not
weather easily
3. Among sedimentary rocks, limestone and other
rocks containing calcite are most easily weathered
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• Rocks with harder minerals weather slower than
  rocks with softer minerals

4. The rate at which sedimentary rocks that are
weathered by mechanical processes are dependent
upon the cementing material
a. Shales and sandstones are not firmly cemented
together and weather easily and break up into
clay and sand particles
b. Conglomerates and those sandstones that are
strongly cemented by silicates may resist
weathering processes for a long time.
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Conglomerate
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B. Amount of exposure
1. The greater the surface area, the greater the
rate of weathering (direct relationship)
a. Fractures and joints increase the surface area
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C. Climate
1. Rainfall and the freezing and thawing produced
by alternating hot and cold weather have the
greatest effect on the rate of weathering
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Increased Surface Area
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2. Cold and moist climates increase mechanical
weathering
3. Warm and moist climates chemical weathering
is dominant

• In general, the more moisture available, the more
  weathering occurs

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D. Topography
1. It is colder at high elevations increasing
ice wedging
2. Steep slopes have weathered rocks pulled down
by gravity and washed away by heavy rains.
a. This exposes fresh mountain surface to be
weathered.