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12 s070502 b_weathering ppt

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12 s070502 b_weathering ppt

  1. 1. Weathering Mechanical and Chemical
  2. 2. What Caused This?
  3. 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. 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. 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
  6. 6. 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. 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. 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.
  9. 9. 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. 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. 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

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