Weathering

1
Weathering

• Mechanical
• and
• Chemical

2
What Caused This?
3
What is Weathering?

• First step to forming soil and sedimentary rock
• Breakdown of rock into smaller pieces
• The smaller pieces do not move to a new location
  until erosion carries them away
• Many types of weathering

4
What is Mechanical Weathering?

• Breakdown of rock into smaller pieces without any
  change in the chemical composition of its
  minerals
• Sometimes called physical weathering
• Rock is torn apart by physical force, rather than
  by chemical breakdown
• Smaller pieces do not move to a new location
  until erosion carries them away

5
Mechanical - Ice Wedging

• Ice Wedging
• Water fills joints of rocks and freezes
• Water expands 10 when it freezes, pushes rock
  apart
• Repeated freeze and thaw cycles over the years
  causes rock to break along joint

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Mechanical - Exfoliation

• Exfoliation or unloading
• Rock breaks off into sheets along joints which
  are parallel to the surface
• Caused by expansion of rock due to uplift and
  removal of surface material that originally
  buried the rock

7
Mechanical - Thermal

• Thermal expansion
• Repeated daily heating and cooling of rock
• Heat causes expansion cooling causes contraction
• Different minerals expand and contract at
  different rates causing the rock to split

8
Mechanical - Biotic

• Biotic means life
• Weathering caused by living organisms
• Plant roots act as a wedge and widen cracks
• Other causes of biotic weathering are digging
  animals, microscopic plants and animals, algae
  and fungi.

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What is Chemical Weathering?

• Breakdown of rock into smaller pieces because of
  change in the chemical composition of its
  minerals
• Chemical reactions break down the bonds holding
  the rocks together, causing them to fall apart
• Chemical weathering occurs in all types of rock
• Rock reacts with water, gases and solutions

10
Chemical - Oxidation

• Oxidation - oxygen combines with other elements
  in rocks to form new types of rock
• New substances are usually much softer than
  original, easier for other forces to break rock
  apart
• Causes a rusting of the rock, often causes a
  color change in the rock

11
Chemical - Carbonation

• Carbonation Carbon dioxide (CO2) is dissolved
  in water making carbonic acid
• Weak acid is formed when CO2 in the air mixes
  with rain. This is the same acid found in soft
  drinks. 
• Acid is too weak to harm plants and animals but
  slowly causes feldspars and limestone to
  decompose