Subaerial Processes

Question 1

Which two subaerial processes are important in the development of coastal landforms?

Answer 1

Weathering and mass movement.

Question 2

What are the three types of weathering important in sediment production and why?

Answer 2

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.

Question 3

What is lithology?

Answer 3

Lithology is the technical term for different rock types.

Question 4

Explanation: Mechanical: Freeze-thaw

Answer 4

Water expands by 9% in volume when it freezes, exerting a force within cracks and fissures; repeated cycles force cracks open and loosen rocks.

Question 5

Vulnerable rocks: Mechanical: Freeze-thaw

Answer 5

Any rocks with cracks and fissures, especially high on cliffs away from salt spray.
Freezing is relatively uncommon on UK coasts.

Question 6

Explanation: Mechanical: Salt crystallisation

Answer 6

The growth of salt crystals in cracks and pore spaces can exert a breaking force, although less than for freeze-thaw

Question 7

Vulnerable rocks: Mechanical: Salt crystallisation

Answer 7

Porous and fractured rocks, e.g. sandstone.

The effect is greater in hot, dry climates, promoting the evaporation and the precipitation of salt crystals.

Question 8

Explanation: Chemical: Carbonation

Answer 8

The slow dissolution of limestone due to rainfall (weak carbonic acid) producing calcium biocarbonate in solution.

Question 9

Vulnerable rocks: Chemical: Carbonation

Answer 9

Limestone and other carbonate rocks

Question 10

Explanation: Chemical: Hydrolysis

Answer 10

The breakdown of minerals to form new clay minerals, plus materials in solution, due to the effect of water and dissolved carbon dioxide.

Question 11

Vulnerable rocks: Chemical: Hydrolysis

Answer 11

Igneous and metamorphic rocks containing feldspar and other silicate minerals.

Question 12

Explanation: Chemical: Oxidation

Answer 12

The addition of oxygen to minerals, especially iron compunds, which produces iron oxides and increases volume contributing to mechanical breakdown.

Question 13

Vulnerable rocks: Chemical: Oxidation

Answer 13

Sandstones, siltstones and shales often contain iron compounds which can be oxidised.

Question 14

Explanation: Biological: Plant Roots

Answer 14

Trees and plants roots growing in cracks and fissures forcing rocks apart.

Question 15

Vulnerable rocks: Biological: Plant roots

Answer 15

An important process on vegerated cliff tops which can contribute to rock falls.

Question 16

Explanation: Biological: Rock boring

Answer 16

There are many species of clams and molluscs that bore into rock, and may also secrete chemicals that dissolve rocks.

Question 17

Vulnerable rocks: Biological: Rock boring

Answer 17

Sedimentary rocks, especially carbonate rocks (limestone) located in the inter-tidal zone.

Question 18

What does mass movement refer to?

Answer 18

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.

Question 19

What are the mass movement processes?

Answer 19

Fall
Topple
Rotational slide/slumping
Flow

Question 20

What is fall?

Answer 20

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.

Question 21

What is topple?

Answer 21

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.

Question 22

What is rotational slide/slumping?

Answer 22

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.

Question 23

What is flow?

Answer 23

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.