Subaerial processes of mass movement and weathering

Weathering

Weathering

• Mechanical Weathering 🔗 Breaks down rocks due to the exertion of physical force, it does not involve any chemical change
• Chemical Weathering 🔗 Involves a chemical reaction & the generation of new chemical compounds
• Biological Weathering 🔗 The action of plants, bacteria or animals | Type | Process | Explanation | Vulnerable rocks | |---|---|---|---| | Mechanical | Freeze-thaw | Water expands when it freezes (approx 9%), exerting force w/in cracks & fissures. Occurs repeatedly, worsening cracks each time | Rocks w/ cracks & fissures | | | Salt crystallisation | The growth of salt crystals in cracks exerts pressure, widening cracks | Porous & fractured rock (sandstone) | | Chemical | Carbonation | Carbonic acid in rain dissolves rocks | Limestone & other carbonate rocks | | | Hydrolysis | Rocks broken down to form new clay minerals & materials in solution due to the impact of water & dissolved CO2 | Igneous & metamorphic | | | Oxidation | O2 added to minerals (especially Iron), ∴ increasing their volume, causing mechanical breakdown | Sandstone, siltstone & shale | | Biological | Plant roots | Tree & plant roots grow in cracks/fissures, forcing rocks apart | Any rock on vegetated cliff tops | | | Rock boring | Species of clams & molluscs/birds bore into rock | Sedimentary rocks, especially carbonate |

Mass Movement

🔗 The movement downslope of rocks, sand, clay, till or soil (caused by gravity)

Mass Movement

Types of Mass Movement

Rockfall	Blocks of rock dislodged by mechanical weathering or by hydraulic action ↳ Often associated with the undercutting of cliffs by the creation of wave-cut notches. Forms a talus scree slope
Rotational slide	A section of cliff remains intact as it moves down a cliff along a curved slip plane ↳ Leaves a crescent-shaped rotational scar above it on the cliff A sequence of slumps like this can result in a terraced cliff profile
Mudflow	Common in weak rock (eg. clay, unconsolidated sediment) ↳ Materials become saturated & lose their cohesion → begin to flow downslope (exacerbated by high tides & heavy rainfall)
Topple	When rock strata have a very steep seaward dip ↳ Undercutting leads to instability causing blocks of material to topple seaward