Rocks and Weathering
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Transcript of Rocks and Weathering
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Rocksand
Weathering
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 therock 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-HorizonLitter layer- leaves
A-HorizonTop Soil – dark colored, sediment, decayed material, insects, worms
B-HorizonLighter color, little or no humus, contains minerals from leaching
C-HorizonSome material leached from B-horizon, partly weathered rock, no humus
Solid rock below soil profile