Weathering, Erosion & Soils

Weathering is the the breakdown of solid rock at or

near the Earth's surface.

Weathering may be mechanical or chemical

• Mechanical weathering is the physical abrasion due to the action of:– Water (Streams, Rivers and Surf)– Ice (Frost, Snow, Glaciers)– Wind

• Chemical weathering is the chemical reaction of minerals with the water and oxygen of our atmosphere.

Mechanical Weathering• Mechanical Action of Streams and Rivers

Mechanical Weathering• By the Action of Ice

Mechanical Weathering• By the action of Wind

Chemical weathering

• By oxidation, hydration, or biological activity

Chemical Weathering:Exfoliation

Chemical Weathering

• Increases with Temperature• Increases with Moisture (Rainfall)• Increases with Acidity• Decreases with Silica Polymerization

(Bowen’s Reaction Series)

Chemical Weathering of Igneous Rock Minerals

• Oxides > Hydroxides• Ferromags > Mg-Fe Clay• Feldspar > Al-Clay + Na+ + K+ + Ca++

• Mica > Al-Fe Clay + Na+ + K+ + Ca++ • Quartz > Quartz Sand

Erosion and Transport

• Erosion is the reduction of exposed landforms.• Transport is the movement of eroded material

down slope.• Transport by water sorts the particles by size.• Because different minerals dominate different

size fractions, the deposited material differs from the parent rock in mineralogy and chemistry.

Weathering Products Are Sorted by Size

• Coarse particles require moving water or wind– Rock grains: Pebbles, Cobbles, Boulders– Quartz: Pebbles and Sand

• Fine particles require standing water.– Clays Very fine (<10 mm)

• Dissolved ions require evaporation– Na+ + K+ + Ca++ Dissolved

Depositional Environments

SoilsSoils• A regolith is any accumulation of fine rock

material on a planetary surface. • A soil is the accumulation of weathered rock

material together with organic matter.• A pedocal is a dry-climate soil containing

soluble calcium minerals (calcite).• A pedalfer is a humid-climate soil rich in Al

and Fe. • A laterite is an extreme pedalfer in tropical

climates.

Soil Types

Laterites are Tropical Soils

Soil Changes in US

Acid Rain

• Results from burning of sulfur-rich fossil fuels (mainly coal).

• Is mainly a problem in humid temperate climates (NE US, Europe).

Acid Mine Drainage

• Results from oxidation of sulfide minerals (pyrite) in unsaturated rock.

• 2FeS2 +7H2O + 2O2 > 2Fe(OH)3 + 4H2SO4

• Pyrite + water + oxygen > limonite + sulfuric acid

• Big Problem in CO

Acid Mine Drainage

Weathering Terms

• Chemical weathering• Mechanical weathering• Spheroidal weathering• Pedocal• Pedalfer• Laterite• Bauxite• Hydration• Oxidation

• Exfoliation• Erosion• Soil• Regolith• Humus• Acid mine

drainage