EEPS (Weathering and Erosion)

Types of Weathering 

• Physical/Mechanical 

• Chemical 

Mechanical Weathering processes

Breaking down rocks into smaller pieces without changing their chemical composition.

• Freeze-thaw (ice wedging). 

• Thermal expansion due to change in temperature.  

• Plants and animals 

Chemical Weathering processes 

• Air, Water, Carbonic Acid 

• Carbonic acid 

• Air pollutants (sulfuric and nitric) 

What can happen during mineral weathering chemically? 

Mineral = new weathered mineral + ions in solution 

Mineral = ions in solution (salt and water) 

Enhanced rock weathering (ERW)

Treating fields with ground basalt
Spreading crushed silicate rocks to accelerate weathering and draw CO₂.. 

Divalent cations 

(2+; Ca, Mg) consume 2 molecules of CO₂ when weathering.  

Monovalent cations

(1+; K, Na) consume 1 molecule of CO2 when weathering.

Susceptibility to chemical weathering 

Least Stable - weather fast 

Most stable weather slowly 

Differential weathering

• Different rocks, different resistance

• Chemical composition and mechanical strength

Weathering 

The physical breakdown and chemical alteration of rock at or near Earth’s surface.

Erosion

The physical removal of material by mobile agents such as water, wind, ice, or gravity. 

Freeze-thaw (Ice Wedging)

Mechanical, caused by repeated freezing and thawing of water in cracks and pores.

Thermal Expansion

Mechanical processes repeated daily or seasonal heating and cooling of rocks causing them to break and crack.

Biological Weathering

Caused by activities of living organisms such as plant roots or burrowing animals.

H2O + CO2 → H2CO3 

Water reacts with carbon dioxide to form carbonic acid, a weak acid that weathers many minerals. 

Outcomes of Chemical Weathering 

1. Transformation into residual mineral plus ions in solution 

2. Complete dissolution into ions in solution. 

Oxidation 

Chemical weathering, where iron-rich material reacts with oxygen to form oxides, like rust. 

Example of Oxidation

Transformation of Olivine (Fe₆SiO₄) into hematite (Fe₂O₃)

Solution (Dissolution)

Chemical weathering in which minerals dissolve in water, effective on carbonates like limestone.

Chemical Equation for limestone

(CaCO₃ + H₂CO₃ → Ca²⁺ + 2HCO₃⁻). Calcite reacts with carbonic acid to form calcium and bicarbonate ions.

Most stable mineral against chemical weathering.

Quartz.

Least stable mineral against chemical weathering

Olivine.

Relationship between mineral stability and crystallization.

Crystallized at high temperature, generally less stable and weather faster. 

Differential Weathering 

Rock masses weather at different rates, often creating uneven surfaces. 

Strong mechanical weathering

Cold temp, and moderate precipitation

Strong Chemical weathering

Hot temp and high rainfall.

Karst Topography

Formed from the dissolution of soluble rocks characterized by sinkholes, caves, and drainage systems.

Mass Wasting

Downslope movement of rock, regolith, and soil under the direct influence of gravity. 

Key factors driving mass wasting

Steepness of slope, presence of water, vegetation, shocks, and the properties of rock/soil.