WEATHERING, EROSION & SOIL

FORMATION

WEATHERING, EROSION, TRANSPORTATION

• Weathering- Physical disintegration and chemical decomposition of rocks

• Erosion- Physical removal• Transportation- Movement of eroded particles• Chemical vs. Physical Weathering• Effects of weathering

– Surface alteration of outcrops– Spheroidal weathering– Differential weathering

Physical Weathering

Transport

Abrasion

WEATHERING, EROSION, TRANSPORTATION

• Weathering- Physical disintegration and chemical decomposition of rocks

• Erosion- Physical removal• Transportation- Movement of eroded

particles• Chemical vs. Physical Weathering• Effects of weathering

– Surface alteration of outcrops– Spheroidal weathering– Differential weathering

Differential Weathering

MECHANICAL WEATHERING

• Disintegration of rocks• Frost Action

– Frost wedging - rock pried apart along joints

• water expands upon freezing (ice wedge)

– Frost heaving

Frost Action

MECHANICAL WEATHERING

• Pressure Release– sheet joint– exfoliation

• exfoliation domes

• Other– Plant growth; Burrowing animals– Pressure of salt crystals– Extreme temperature changes

• Mechanical weathering increases surface area facilitating chemical weathering

Exfoliation

Organic Action

Mechanical Weathering

Growth of salt crystal in arid/semi-arid regions can split rocksHeat and cold extremes can also cause rock breakage

CHEMICAL WEATHERING

• Decomposition of rock to form new substances– Equilibrium

• Role of Oxygen– Fe in ferromagnesian minerals becomes

oxidized • Hematite• Limonite

Chemical Weathering

• Role of Acid– Hydrogen ions in water– pH=-Log[H+] Acid/Base

• Carbonic Acid H2CO3

– CO2 + H2O -> H2CO3

– H2CO3 -> H+ + HCO3- (in water)

– Solution weathering- Karstic Features• Calcite (in limestone) dissolves in acidic water• fluted (channeled) rock surface• caves

Chemical Weathering• Role of Acid

– Hydrogen ions in water– pH=-Log[H+] Acid/Base

• Carbonic Acid H2CO3

– CO2 + H2O -> H2CO3

– H2CO3 -> H+ + HCO3- (in water)

– Solution weathering- Karstic Features• Calcite (in limestone) dissolves in acidic water• fluted (channeled) rock surface• caves

KARST

Chemical Weathering

• Chemical weathering of feldspar– H+ + feldspar -> clay mineral

• Chemical weathering of other minerals• Weathering and climate• Weathering Products

Chemical Weathering

• Chemical weathering of feldspar– H+ + feldspar -> clay mineral

• Chemical weathering of other minerals• Weathering and climate• Weathering Products