Sub aerial processes

Question 1

Weathering

Answer 1

The in situ breakdown of rocks by chemical, mechanical or biological agents. Does not involve any movements

Question 2

Mechanical weathering

Answer 2

Breaks down rocks by exertion of a physical force, which does not cause any chemical change

Question 3

Type of mechanical weathering

Answer 3

• Freeze-thaw weathering

- Salt crystallisation

Question 4

Freeze-thaw weathering

Answer 4

water expands when it freezes, exerts force within cracks and fissures, repeated cycles of this forces cracks to open.

Question 5

What rocks are vulnerable to freeze-thaw weathering?

Answer 5

Rocks with cracks and fissures. Uncommon on UK coasts

Question 6

Salt crystallisation

Answer 6

Growth of salt crystals in cracks exerts a breaking force, but this is less than for freeze thaw weathering

Question 7

Which rocks are vulnerable to salt crystallisation?

Answer 7

Porous and fractured rocks. Has a greater effect in dry climates, where the evaporation and precipitation of salt crystals is promoted.

Question 8

Chemical weathering

Answer 8

Involves a chemical reaction and the generation of new chemical compounds.

Question 9

Types of chemical weathering

Answer 9

• carbonation
• hydrolysis
• oxidation

Question 10

Carbonation

Answer 10

Slow dissolution of limestone due to rainfall, producing sodium bicarbonate in solution

Question 11

which rocks are vulnerable to carbonation?

Answer 11

Limestone and other carbonate rocks

Question 12

Hydrolysis

Answer 12

Breakdown of materials to form new clay minerals, plus materials in solution due to the effect of water and dissolved co2.

Question 13

Which rocks are vulnerable to hydrolysis?

Answer 13

Igneous and metamorphic rocks containing feldspar and other silicate materials

Question 14

Oxidation

Answer 14

Addition of oxygen to minerals, especially iron compounds, produces oxides, increases volume contributing to mechanical breakdown

Question 15

Which rocks are vulnerable to oxidation?

Answer 15

Sandsones, siltstones and shale contain iron compounds which can be oxidised.

Question 16

Biological weathering

Answer 16

Often speeds up mechanical and chemical weathering through the action of plants, bacteria, or animals.

Question 17

Types of biological weathering

Answer 17

• plant roots

- rock boring

Question 18

Plant roots

Answer 18

Trees and plant roots growing into cracks and fissures can force rocks apart

Question 19

Which rocks are vulnerable to plant roots?

Answer 19

Vegetated cliff tops, which can contribute to rock fall.

Question 20

Rock boring

Answer 20

Many species of clams and molluscs that bore into rocks, and many also secrete chemicals that dissolve rocks.

Question 21

Which rocks are vulnerable to rock boring?

Answer 21

sedimentary rocks, especially carbonate rocks, limestone, which are located in the inter tidal zone.

Question 22

How fast is the rate of weathering?

Answer 22

It is very slow

Question 23

How does weathering contribute to coastal recession?

Answer 23

• weakens rocks and makes them more vulnerable to erosion and mass movement processes
• some strata = more vulnerable, produces wave cut notches and decreases overall cliff stability.

Question 24

Mass movement

Answer 24

the downslope movement of rock and soil.

Question 25

Types of mass movement

Answer 25

• Fall
• Topple
• Rotational slides/slumping
• Flow

Question 26

Fall

Answer 26

• Rockfalls are a rapid form of mass movement
• blocks of rock dislodged by mechanical weathering or hydraulic action erosion
• undercutting of cliffs by creation of wave cut notches
• leads to large falls

Question 27

Topple

Answer 27

• geological structure influences topples

- rock strata with very steep seaward dip, undercut by erosion, unstable blocks of material topple forward

Question 28

Rotational slide/slumping

Answer 28

• mass movement along a curved failure surface
• huge masses of material slowly rotate downslope over periods of time
• create a back scar and terraced cliff profile

Question 29

Flow

Answer 29

• common in real rocks such as clay or unconsolidated sands
• materials become saturated, lose their cohesion and flow downslope
• heavy rainfall and high waves and tides contribute to saturation

Question 30

What causes a rotational slide/slump?

Answer 30

• bedding plane between impermeable clay and permeable sand dips seaward, promotes mass movement
• cracks develop in cliff top during dry weather, become routes rainwater can take to sand
• heavy rain saturates permeable sands, loading the cliff material
• water percolates through permeable sand but is forced to move along sand/clay boundary as clay is impermeable. Contributes to high pore water pressure in the sand and creates pressure within the cliff
• Erosion at base of cliff by marine processes undercuts cliff from below
• curved failure surfaces develop, and whole cliff begins to rotate.