Rocks and Weathering

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RocksandWeathering

• Chapter 8.1

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Weathering- the breaking of rock
into smaller fragments

• Mechanical weathering breaks rock
• apart without changing the chemical
• composition
• Examples
• Rocks colliding with other rocks in rivers
• Tree roots lifting rock
• Ice wedging caused by freezing and thawing

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• Chemical weathering reaction of air,
• water and/or other substances with the
• minerals in rock

The composition of the rock is changed
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• Water is the main cause of chemical weathering
• It dissolves away some minerals leaving a
  different composition behind
• Compounds in air combine with water and react
  with minerals upon contact
• Some metals react with oxygen and water
• (oxidation)

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• Acids cause chemical weathering
• Water and carbon dioxide form
• carbonic acids which dissolve
• calcite and create caves
• Plant roots and decaying plants create acids that
• dissolve minerals making rock weak

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Climate effects the speed of weathering

• - Chemical weathering is most rapid in warm,
  moist areas.
• - Mechanical weathering is most rapid where
  freezing and thawing occur.

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Chemical or Mechanical?

• Colonies of lichens growing on the surface of
  rocks.
• Chemical

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Chemical or Mechanical?

• The wedging of tree roots along natural joints in
  granite outcrops
• Mechanical

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Chemical or Mechanical?

• Solution of limestone by acidic groundwater
• Chemical

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Chemical or Mechanical?

• The oxidation of minerals which contain iron
• Chemical

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Chemical or Mechanical?

• Animal burrows dug in rock which let in water and
  air
• Mechanical

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Chemical or Mechanical?

• Repeated freezing and thawing of water cracks
  rock or joints
• Mechanical

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Chemical or Mechanical?

• The action of water, salt and air on car fenders
  and panels

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Chemical or Mechanical?

• The action of water, salt and air on car fenders
  and panels
• Chemical

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Chemical or Mechanical?

• The sun fading paint on houses and cars
• Chemical

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Chemical or Mechanical?

• Formation of potholes in streets during severe
  winters
• Mechanical

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Chemical or Mechanical?

• Lifted sections of sidewalk along tree-lined
  streets
• Mechanical

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How Soil Forms

• Section 8.2

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Soil Profile

• Soil a mixture of weathered rock and
• organic matter
• - can take hundreds of years to form
• - varies in thickness

Humus decaying plants and animals that mix
with weathered rock
Soil Profile - shows the layers of soil and
weathered rock
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O-Horizon Litter layer- leaves
A-Horizon Top Soil dark colored, sediment,
decayed material, insects, worms
B-Horizon Lighter color, little or no humus,
contains minerals from leaching
C-Horizon Some material leached from B-horizon,
partly weathered rock, no humus
Solid rock below soil profile