weathering: disintegration of rocks in situ physical weathering size and shape of rocks altered but...
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Weathering: Types and Rate of Weathering
Weathering: Disintegration of rocks
in situPhysical
Weathering Size and shape of rocks
altered but not the chemical composition
Angular and coarse end-products
Some involvement of water in the processes (e.g. freeze-thaw and salt crystal growth)
Effective in extreme climate conditions
Chemical Weathering
Physical structure and chemical composition of rocks altered
Finer end-products (e.g. clay and sand)
Water (rainwater, seawater) is important as the main solvent in all processes
Effective in vegetated areas and hot and wet climate
Chemical Weathering
Hydrolysis
Carbonation
Oxidation
Solution
Karst Landscape
Insolation Weathering
Pressure Release
Salt Crystal Growth
Freeze-Thaw Action/ Frost Shattering
Factors affecting type and rate of weathering
Factor 1: Rock Hardness
Rock Hardness- dependent on minerals that form rocks and how minerals are cemented together
Igneous stronger than Sedimentary rocks. Why?
Least important factor since all rocks ultimately experience weathering once they are exposed to weathering agents
Factor 2: Mineral composition
Influence rock resistance to chemical weathering
Weaker minerals: calcium carbonate, olivine and pyroxene
Stronger minerals: quartz
Influence also physical weathering like insolation weathering because of differences in coefficient of expansion and contraction of minerals
Factor 3: Grain size of rocks
Coarse-grained rocks weathered down faster than fine-grained rocks
When minerals susceptible to changes are altered (e.g. feldspar), larger gaps are formed, weakened structure, larger gap provides bigger surface area for further chemical attack
Factor 4: Lines of Weakness of rocks
Lines of weakness (e.g. cracks, joints, bedding planes) found in rocks make them more susceptible to both physical and chemical weathering. How?
The more well-jointed the rock is, the faster the rate of physical, chemical and even biological weathering
Factor 5: Relief
On flat land, soil and weathered materials can retain water which seeps through them and acts on the underlying rocks chemically
On slopes, mass movements, like landslides and slumping, expose more underlying rocks for physical weathering.
Chemical weathering less effective on steep slopes as water flows away
Factor 6: Vegetation cover
Vegetation cover can retain rainwater and keeps underlying rocks moist for chemical weathering to take place
Biological weathering common too
Factor 7: Human activities
How do human activities contribute to weathering?
Weathering regions of the world in relation to mean annual
temperature and precipitation (Peltier,1950)