ch 14 weathering two types: 1.physical or mechanical 2.chemical
TRANSCRIPT
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Ch 14Weathering
Two Types:
1.Physical or Mechanical
2.Chemical
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Mechanical Weathering
• Rock is broken down into smaller pieces by physical means.
• Agents: wind, water, ice, gravity, plants & animals.
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EXFOLIATION
• Rocks break into curved sheets that peal away
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Ice Wedging
• Water gets into cracks and freezes
• Freeze/Thaw cycle splits rock
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ABRASION WIND
WATER
ICE
Wearing away of rocks by other rock particles
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ROOT WEDGING
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Animals - Burrowing
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Chemical Weathering
• Rock is broken down by chemical interaction with the environment.
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OXIDATION (rusting)• Elements combine
with oxygen to form rust
• Iron bearing rocks
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HYDROLYSIS: Minerals decompose in water as hydrogen replaces cations infeldspar (turns into clay).
HYDROLYSIS: Minerals dissolve in water.
LEACHING: Water carries dissolved minerals away,forms beds of aluminum(bauxite)
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CARBONATION: Limestone caves
Carbon Dioxide and water react to form carbonic acid...Carbonic acid “eats” limestone.
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Acid Precipitation
• Acids formed from the burning of fossil fuels combining with atmospheric water; bad for plants & structures.
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Factors that affect Rates of Weathering
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DIFFERENTIAL WEATHERING
Softer, less-resistant rock wears away, leaving harder resistant rock behind.
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Bryce Canyon “Hoodoos”
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Rock composition
• Sedimentary rocks containing calcites weather rapidly (limestone).
• Quartz containing rocks are strong and weather slowly
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Surface area
The more surface area per volume, the faster the rock’s weathering rate.
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Fractures and Joints
• Increase surface area of rock
• Allow weathering to happen faster
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Climates
• Hot/Cold climates with freeze/thaw cycles have fastest weathering rates.
• Hot/Dry climates weather the least.
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Topography
• Elevation or slope of the land.
• High Elevations – cold temp, ice wedging
• Steep Slopes – gravity pulls rock down
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Human Activities
• Mining
• Construction
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Plants and Animals
• Roots, Burrowing, Waste (Bat Guano)