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