Weathering and Soil

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Lecture 6 Weathering and Soil
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Physical Geology
Lecture Outline
I Weathering A) Definitions B) Mechanical
Weathering i. Frost Action ii. Pressure
Release iii. Other Mechanical
Processes C) Chemical Weathering i. Agents
a) Acids b) Oxidation c) Solution
Weathering ii. Examples II Soils A) Definition
s B) Soil Horizons and Classification C) Soil
Character and Thickness D) Organic Activity and
Soil Development E) Soils and Climate F) Paleoso
ls III Conclusions
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Physical Geology
WeatheringDefinition
weathering the destructive processes by which
rocks are changed on exposure to atmospheric
agents at or near the earth's surface, with
little or no transport of the altered material.
Specifically, it is the physical disintegration
and chemical decomposition of rock that produce
an in-situ layer of waste and prepare sediments
for transportation.
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Physical Geology
WeatheringDefinition
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Physical Geology
WeatheringResults

• Smaller Pieces of Rock
• Increased Surface Area
• Conduits for Water

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Physical Geology
WeatheringProcesses
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Physical Geology
Mechanical WeatheringFrost Action
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Physical Geology
Mechanical WeatheringPressure Release -
Exfoliation
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Physical Geology
Mechanical WeatheringOther Processes

• Salt Crystal
• Plant Growth
• Burrowing Animals

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Physical Geology
Chemical Weathering
chemical weathering the process of weathering by
which chemical reactions(hydrolysis, hydration,
oxidation, carbonation, ion exchange and
solution) transform rocks and minerals into new
chemical combinations that are stable under
conditions prevailing at or near the earth's
surface.
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Physical Geology
Chemical WeatheringAgents

• Acids
• Oxidation
• Solution Weathering

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Physical Geology
Chemical WeatheringAgents - Acids
acid chemical compound that gives off hydrogen
ions (H) when they dissociate in water
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Physical Geology
Chemical WeatheringAgents - Oxidation
oxidation the process of combining w/ oxygen

• Hematite
• Limonite

4Fe 3O2 -----gt 2Fe2O3
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Physical Geology
Chemical WeatheringAgents - Solution Weathering
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Physical Geology
Chemical WeatheringProducts
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Physical Geology
Chemical WeatheringChemical Weathering of
Feldspar
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Physical Geology
WeatheringFactors That Influence Weathering
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Physical Geology
WeatheringClimate and Weathering
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Physical Geology
SoilDefinitions
(1) any kind of loose, unconsolidated earth
material (engineering/construction) (2) layer
of weathered, unconsolidated material on top of
bedrock (geology) (3) horizons of weathered,
unconsolidated material that contains
organic matter and is capable of supporting
plant growth (soil science)
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Physical Geology
SoilsSoil Horizons and Classification
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Physical Geology
SoilsCharacter and Thickness

• Slope
• Age
• Climate

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Physical Geology
SoilsOrganic Activity
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Physical Geology
Physical Geology
SoilsPaleosols