Mechanical and Chemical Weathering

Weathering and Erosion

examples of exogenic processes that occurs on the surface of the Earth.

Weathering

• process of breakdown of rocks to smaller bits.

• “How rocks disintegrates?”

• chemical and physical breakdown of rocks

Erosion

movement of Earth materials from one place to another.

Mechanical and Chemical Weathering

Two classifications of Weathering

Mechanical Weathering

alteration of rocks in terms of their size, shape and appearance without changing their chemical composition.

Frost Wedging

expansion of water as it freezes between the cracks in the rocks.

Thermal Expansion & Contraction

repeated heating and cooling of materials cause rigid substances to crack and separate.

Exfoliation

• as the underlying rock is exposed, there is less pressure on them and they expand, causing the rigid layers to cracked.

• often form a dome.

Abrasion

moving sediments or rock sections can break off pieces from a rock surface they strike.

Wind and Water

Two agents of Abrasion

Wind

agent of abrasion which carries blown away tiny bits of minerals and causes abrasion to the rocks

Water

an agent of abrasion that is cause by the impact of waves, tides and current that breaks the rocks.

Plant Growth/Wedging

the roots of plants and animals seeks space for them to grow causing the rocks to weather.

Chemical Weathering

processes that change the chemical composition of rocks.

Dissolving (Dissolution)

Prescence of solvent (commonly water) and solute such as acid that dissolves minerals from a rock body.

Acidic Rain

strong to calcites

Carbonic Acid

easily weathers marble and limestone

Oxidation

• water + oxygen + iron = RUST

• ex. Pyrite to Limonite

Hydrolysis

• = means water, = to breakdown

• minerals may combine with water to form new mineral.

• ex. Feldspar to Kaolinite

1. Climate

2. Plants & Animals

3. Time

4. Mineral Compostion

Factors of Chemical Weathering

Climate

wet and warm maximizes chemical reactions

Plants/Animals

living organism secrete substances that react with rock.

Time

longer contact means greater change

Mineral Composition

some minerals are more susceptible to change than others.