Weathering and Soils

The Rock Cycle

The Rock Cycle

Weathering Breakdown 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

Never Safe From Weathering

Weathering Rates

Differential Weathering and Erosion

Differential Weathering and Erosion

Mass-Wasting Movement of Large Amounts of Material Downhill under Gravity Creep Mudflows Slump Rockfalls Avalanches

Surface Area and Weathering

Surface-Volume Effects

Spheroidal Weathering

Spheroidal Weathering and Exfoliation

Spheroidal Weathering

Joints and Spheroidal Weathering

What Determines Soil Type Climate Vegetation Drainage Time Parent Material Residual - Transported Least Important Factor for Mature Soils

Soil Formation Young Soils Strongest Influence Is Parent Material Mature Soils Strongest Influences: Climate, Vegetation, Drainage

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

Soil Horizons and Profiles Layers in Soil Not Deposited, but Zones of Chemical Action Soil Profile Suite of Layers at a Given Locality

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

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

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

Degree of Weathering and B Horizon Development Little Slight Moderate "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