Geo - Physical & Chemical Weathering

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weathering

process which leads to surface and sub-surface degradation

• causes net lot of mass

• changes strength, permeability, or particle size

chemical weathering

changes composition

mechanical/physical weathering

changes size

causes of physical weathering

• pressure

• freeze/thaw

• temperature

• crystallization

• wetting/drying

exfoliation

1. rock is formed underground in high P

2. rock rises up

3. rock reaches surface and expands due to low P

4. expansion causes cracks (exfoliation)

hydration/desiccation

expansion and contraction through wetting and drying

• water expands

• evaporation compresses

crystallization of salts

salt evaporates leaving solids that expand and fracture

frost wedging

ice expands in cracks and breaks rocks

how much does water expand when frozen?

9%

consequences of physical weathering

• reduces rocks to smaller fragments

• increases exposed surface area of rock, making it more prone to weathering

agents of chemical weathering

• water

• oxygen

• carbon dioxide

• living organisms

carbonic acid H2CO3

CO2 is the most soluble of atmospheric agents (dissolves in water)

• is an important agent in hydrolysis and dissolution

minerals that are the first to crystallize are the first to weather

dissolution

rocks are dissolved by water

• co2 dissolves in water to form carbonic acid

• water + carbonic acid completely dissolve minerals

ex. sinkholes

hydrolysis

hydrogen and hydroxyl ions in water react with minerals creating new minerals

oxidation

loss of electrons

strongly affects colors

affects anything with iron