Weathering

Weathering

• The Chemical and physical breakdown of material (rock).

Disintegration

• The breaking up of material into smaller pieces• Also called Physical or Mechanical Weathering

– Thermal Expansion– Frost Wedging– Plant and Animal Action– Unloading

Thermal ExpansionMaterial expands when it gets warmer.

The outside of a rock will get hotter than the inside during the day and colder at night, therefore the outer part expands and contracts more than the inner part.

Exfoliation

Thermal Expansion• Examples:

– Expansion Joints on bridges.

– Ice crackling in water– Hot water on cold glass– Cold water on hot glass

Frost Wedging

•

Frost or Ice Wedging

• What conditions would cause a lot of ice wedging?

How potholes form

Plant and Animal Action•

Plant Roots

•

Root damage to sewer lines

•

Unloading & Jointing

•

Jointing

Decomposition

• The chemical changing of material into a new material.

• Most important agent involved is water.• Also called Chemical Weathering

– Acids– Hydrolysis– Oxidation

Acids• Carbonic Acid or

Carbonation

H2O + CO2 + CaCO3  -->

Ca+2 + HCO3-

Acids• Organic Acids

– Lichens– Plants– Animals

• Sweat• Urine

Hydrolysis and Hydration• Reacting with water

– KAlSi3O8 + H20 --> Al2Si2O5(OH)4 + SiO2 + K(OH)

Oxidation

• Rust

Fe+2 +O2 --> Fe2O3

Chemical helps Physical by making the rock weaker

•

Physical helps Chemicalby increasing the surface area

DifferentialWeathering

Differential Weathering

•

Factors that Influence the Rate of Weathering

Rates of Weathering

Rates of Weathering of Clean Rock Surfaces (micro-meters/1000years)

Rock Type Cold Climate Warm, Humid Climate

Basalt 10 100

Granite 1 10

Marble 20 200

60 years of weathering

• 60 years of weathering and plant growth.

Effect of humid

climate on

Cleopatra’s Needle.

• Weathering• Mass Wasting• Erosion

The Result of Weathering

The End