Soils, Weathering, and Erosion

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Soils, Weathering, and Erosion

• Where the geosphere and the biosphere meet

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Learning Targets

1. Define mechanical and chemical weathering
2. Discuss agents of weathering
3. Give examples of each type of weathering

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Soil Forming Processes

1. Weathering process that changes solid rock into
   sediments
2. Erosion process that moves sediments
3. Sedimentation depositing of rock pieces

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Weathering
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Erosion
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Sedimentation
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Weathering

• Large rocks and mountains ? sediment
• Sediment sizes
• Boulders
• Gravel
• Sand
• Silt
• Clay
• What processes act on weathered sediments?
• Erosion (movement)
• Sedimentation (deposition)

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Weathering

• Weathering only happens at the surface
• Occurs in 2 forms
• Mechanical change in shape or size
• Also known as physical weathering
• Chemical change in composition

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Mechanical Weathering (Physical Weathering)
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Chemical weathering
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Mechanical Weathering (Physical Weathering)

• 3 main types
• Ice wedging
• Cycles of freezing and thawing
• Abrasion
• Physical contact and friction
• Biological weathering
• Roots, burrowing animals, fungi, lichens, humans

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Ice wedging
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Abrasion
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Biological weathering
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Mechanical Weathering

• Increases surface area
• Increased surface area leads to quicker
  weathering. Why?
• More rock is exposed to the atmosphere less rock
  is protected from water and oxygen

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Increasing surface area
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Chemical weathering

• Creates new minerals or compounds
• Different composition not just different size
• Different minerals are stable at surface than at
  depth
• Mainly caused by
• Water dissolves minerals
• Oxygen combines to form oxides
• Carbon Dioxide makes water acidic

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Oxidation
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Hydrated obsidian
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Oxidized ultramafic rock
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Rust chemical weathering of Iron
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Chemical Weathering

1. Some organisms release chemicals that break down
   rocks and minerals
2. Fungi and bacteria are very important parts of
   chemical weathering

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Lichens colonizing a lava flow
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Differential weathering

• Weather rates speed up based on
• Rock and Mineral Type
• Sedimentary rocks weather fastest
• Climate type
• Temperature increases Chemical reactions more
  rapid
• Precipitation increases More water allows more
  chemical reactions