Weathering and Soils

1
Weathering and Soils
2
(No Transcript)
3
The Rock Cycle
4
The Rock Cycle
5
WeatheringBreakdown of Rock near the Surface Due
to Surface Processes

• Chemical Alteration
• Solution Leaching
• Biological Action
• Hydration
• Mechanical
• Impact
• Wedging Frost, Plant Roots, Salt Crystal
  Growth, Expansion of Hydrated Minerals

6
Never Safe From Weathering
7
Weathering Rates
8
Differential Weathering and Erosion
9
Differential Weathering and Erosion
10
Mass-WastingMovement of Large Amounts of
Material Downhill under Gravity

• Creep
• Mudflows
• Slump
• Rockfalls
• Avalanches

11
Surface Area and Weathering
12
Surface-Volume Effects
13
Spheroidal Weathering
14
Spheroidal Weathering and Exfoliation
15
Spheroidal Weathering
16
Joints and Spheroidal Weathering
17
What Determines Soil Type

• Climate
• Vegetation
• Drainage
• Time
• Parent Material
• Residual - Transported
• Least Important Factor for Mature Soils

18
Soil Formation

• Young Soils
• Strongest Influence Is Parent Material
• Mature Soils
• Strongest Influences Climate, Vegetation,
  Drainage

19
Soil Formation Processes

• Leaching from Surface
• K, Mg, Na
• Ca
• Si
• Al, Fe
• Accumulation beneath Surface
• Al, Fe in Humid Climates
• Ca in Arid Climates

20
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

21
Principal Soil Horizons

• O - Organic (Humus) Often Absent
• A Leaching
• K, Mg, Na, Clay Removed
• E - Bleached Zone - Present Only in Certain Soils
• B Accumulation
• Absent in Young Soils
• Distinct in Old Soils
• Al, Fe, Clay (Moist)
• Si, Ca (Arid)
• C - Parent Material

22
Limits of Soil Formation

• Balance Between
• Downward Lowering of Surface
• Downward Migration of Horizons
• If erosion rapid or soil evolution slow, soils
  may never mature beyond a certain point.
• Extremely ancient soils may have lost everything
  movable

23
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

24
"The 7th Approximation"

• U.S. Soil Conservation Service
• 12 Soil Orders

25
"The 7th Approximation"
Degree of Weathering and B Horizon Development Degree of Weathering and B Horizon Development Degree of Weathering and B Horizon Development Degree of Weathering and B Horizon Development Degree of Weathering and B Horizon Development Degree of Weathering and B Horizon Development
Little Slight Slight Moderate Large Extreme
Entisols Aridisols Aridisols
Inceptisols Inceptisols Alfisols
Spodosols Ultisols
Mollisols Oxisols
Soils Defined by Special Constituent Materials Soils Defined by Special Constituent Materials Soils Defined by Special Constituent Materials Soils Defined by Special Constituent Materials Soils Defined by Special Constituent Materials Soils Defined by Special Constituent Materials
Andisols Andisols Volcanic Ash Volcanic Ash Volcanic Ash Volcanic Ash
Histosols Histosols Peat, Organic Matter Peat, Organic Matter Peat, Organic Matter Peat, Organic Matter
Vertisols Vertisols Self-Mixing Clay Soils Self-Mixing Clay Soils Self-Mixing Clay Soils Self-Mixing Clay Soils
Gelisols Gelisols Soils on Permafrost Soils on Permafrost Soils on Permafrost Soils on Permafrost
26
Soils of the U.S.
27
Typical Soil Profile (Spodosol)
28
Aridisol, Kuwait
29
UltisolsAlabamaTennessee
30
Oxisol, California (a Paleosol)
31
Paleosol, Scotland