Types of Weathering Flashcards
Give two examples of mechanical weathering
Freeze-thaw and salt crystallisation
Name three types of chemical weathering
Carbonation, hydrolysis and oxidation.
Name two types of biological weathering
Plant roots and rock boring.
What is freeze-thaw?
Water expands by 9% in volume when freezing, exerting a force within cracks and fissures; repeated cycles force cracks open and loosen rocks.
What rocks are vulnerable to freeze-thaw?
Any rocks with cracks and fissures, especially high up cliffs away from salt spray. Freezing is relatively uncommon on UK coasts, especially in the South, and the salt spray can reduce its effect even further.
What is salt crystalisation?
The growth of salt crystals in cracks and pore spaces can exert a breaking force, although less than for freeze thaw.
What rocks are vulnerable to salt crystallisation?
Porous and fractured rocks, for example sandstone. The effect is greater in hotter, drier climates where evaporation and the precipitation of salt crystals is more pronounced.
What is carbonation?
The slow dissolution of limestone due to rainfall (weak carbonic acid, pH 5.6) producing calcium bicarbonate in solution.
What rocks are vulnerable to carbonation?
Limestone and other carbonate rocks.
What is hydrolysis?
The breakdown of minerals to form new clay minerals, plus materials in solution, due to the effect of water and dissolved CO2.
What rocks are vulnerable to hydrolysis?
Igneous and metamorphic rocks containing feldspar and other silicate minerals.
What is oxidation?
The addition of oxygen to minerals, especially iron compounds, which produces iron oxides and increases volume contributing to mechanical breakdown.
What rocks are vulnerable to oxidation?
Sandstones, siltstones and shales often contain iron compounds that can be oxidised.
What are plant roots?
Trees and plants roots growing in cracks and fissures forcing rocks apart.
What rocks are vulnerable to plant roots?
An important process on vegetated cliff tops that can contribute to rockfalls.
