Download Weathering and Soils

Earth Science Unit 1.4:
Weathering and Soils
The Rock Cycle
Weathering
The breakdown of rock near the surface
due to surface processes, such as:
Chemical Alteration
– Solution & leaching of water
– Biological action
– Hydration
Mechanical
– Impact
– Wedging: Frost, Plant Roots, Salt Crystal Growth,
Expansion of Hydrated Minerals
Weathering Rates
Differential Weathering and Erosion
Differential
Weathering
and Erosion
Mass-Wasting
Movement of Large Amounts of Material
Downhill under Gravity
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Creep
Mudflows
Slump
Rockfalls
Avalanches
Surface Area
and
Weathering
Spheroidal Weathering
Spheroidal Weathering and Exfoliation
Spheroidal Weathering
Joints and Spheroidal Weathering
What Determines Soil Type
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Climate
Vegetation
Drainage
Time
Parent Material
– Residual - Transported
– Least Important Factor for Mature Soils
Soil Formation Processes
Leaching from Surface
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K, Mg, Na
Ca
Si
Al, Fe
Accumulation beneath Surface
– Al, Fe in Humid Climates
– Ca in Arid Climates
Soil Horizons and Profiles
Soil Horizons
• Layers in Soil
• Not Deposited, but Zones of Chemical Action
Soil Profile
• Suite of Layers at a Given Locality
Principal Soil Horizons
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O - Organic (Humus) Often Absent
A – Leaching (Clay Removed)
E - Bleached Zone - Only in Certain Soils
B – Accumulation
– Absent in Young Soils
– Distinct in Old Soils
– Al, Fe, Clay (Moist)
– Si, Ca (Arid)
• C - Parent Material (bedrock)
Soil Classification
This may be the most
difficult classification
problem in science
because of the many
factors involved.
Varied Bases for
Classification
• Parent Material
• Special Constituent
Materials
• Maturity
• Structure
• Climate & Vegetation
Multiple Objectives
• Scientific
– Genesis & Evolution
• Agricultural
– Fertility
– Most Effective Use
• Engineering
– Slope Stability
– Expansion and
Shrinkage
– Stability of
Excavations
"The 7th Approximation"
• U.S. Soil Conservation Service
• 12 Soil Orders
"The 7th Approximation"
Degree of Weathering and B Horizon Development
Little
Slight
Moderate Large
Extreme
Entisols
Aridisols
Inceptisols Alfisols
Spodosols Ultisols
Mollisols
Oxisols
Soils Defined by Special Constituent Materials
Andisols
Volcanic Ash
Histosols
Peat, Organic Matter
Vertisols
“Self-Mixing” Clay Soils
Gelisols
Soils on Permafrost
Soils of the U.S.
Typical
Soil Profile
(Spodosol)
Aridisol, Kuwait
Ultisols:
Alabama
Tennessee
Oxisol, California (a Paleosol)
Paleosol, Scotland