Subaerial Processes Flashcards
Which two subaerial processes are important in the development of coastal landforms?
Weathering and mass movement.
What are the three types of weathering important in sediment production and why?
Mechanical (physical) weathering: Breaks down rocks by the exertion of a physical force and does not involve any chemical change.
Chemical weathering: Involves a chemical reaction and the generation of new chemical compounds.
Biological weathering: Often speeds up mechanical or chemical weathering through the action of plants, bacteria or animals.
What is lithology?
Lithology is the technical term for different rock types.
Explanation: Mechanical: Freeze-thaw
Water expands by 9% in volume when it freezes, exerting a force within cracks and fissures; repeated cycles force cracks open and loosen rocks.
Vulnerable rocks: Mechanical: Freeze-thaw
Any rocks with cracks and fissures, especially high on cliffs away from salt spray.
Freezing is relatively uncommon on UK coasts.
Explanation: Mechanical: Salt crystallisation
The growth of salt crystals in cracks and pore spaces can exert a breaking force, although less than for freeze-thaw
Vulnerable rocks: Mechanical: Salt crystallisation
Porous and fractured rocks, e.g. sandstone.
The effect is greater in hot, dry climates, promoting the evaporation and the precipitation of salt crystals.
Explanation: Chemical: Carbonation
The slow dissolution of limestone due to rainfall (weak carbonic acid) producing calcium biocarbonate in solution.
Vulnerable rocks: Chemical: Carbonation
Limestone and other carbonate rocks
Explanation: Chemical: Hydrolysis
The breakdown of minerals to form new clay minerals, plus materials in solution, due to the effect of water and dissolved carbon dioxide.
Vulnerable rocks: Chemical: Hydrolysis
Igneous and metamorphic rocks containing feldspar and other silicate minerals.
Explanation: Chemical: Oxidation
The addition of oxygen to minerals, especially iron compunds, which produces iron oxides and increases volume contributing to mechanical breakdown.
Vulnerable rocks: Chemical: Oxidation
Sandstones, siltstones and shales often contain iron compounds which can be oxidised.
Explanation: Biological: Plant Roots
Trees and plants roots growing in cracks and fissures forcing rocks apart.
Vulnerable rocks: Biological: Plant roots
An important process on vegerated cliff tops which can contribute to rock falls.
Explanation: Biological: Rock boring
There are many species of clams and molluscs that bore into rock, and may also secrete chemicals that dissolve rocks.
Vulnerable rocks: Biological: Rock boring
Sedimentary rocks, especially carbonate rocks (limestone) located in the inter-tidal zone.
What does mass movement refer to?
The downslope movement of rock and soil. It is an umbrella term for a wide range of specific movements including landline, rockfall and rotational slide.
What are the mass movement processes?
Fall
Topple
Rotational slide/slumping
Flow
What is fall?
Rockfall, or blockfalls, are a rapid form of mass movement.
On coasts, blocks of rock can be dislodged by mechanical weathering, or by hydraulic action erosion.
Undercutting of cliffs by the creation of wave-cut notches can lead to large falls and talus scree slopes at their base.
What is topple?
Geological structure influences topples.
Where rock strata have a very steep seaward dip, undercutting by erosion will quickly lead to instability and blocks of material toppling seaward.
What is rotational slide/slumping?
Mass movement can occur along a curved failure surface.
In the case of a rotational slide, huge masses of material can slowly rotate downslope over periods lasting from days to years.
Water plays an important role in rotational slides.
Rotational slides create a back-scar and terraced cliff profile.
What is flow?
Flows are common in weak rocks such as clay or unconsolidated sands.
These materials can become saturated, lose their cohesion and flow downslope.
Heavy rainfall combined with high waves and tides can contribute to saturation.
