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Flashcards in Sub aerial processes Deck (30)
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1
Q

Weathering

A

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

2
Q

Mechanical weathering

A

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

3
Q

Type of mechanical weathering

A
  • Freeze-thaw weathering

- Salt crystallisation

4
Q

Freeze-thaw weathering

A

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

5
Q

What rocks are vulnerable to freeze-thaw weathering?

A

Rocks with cracks and fissures. Uncommon on UK coasts

6
Q

Salt crystallisation

A

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

7
Q

Which rocks are vulnerable to salt crystallisation?

A

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

8
Q

Chemical weathering

A

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

9
Q

Types of chemical weathering

A
  • carbonation
  • hydrolysis
  • oxidation
10
Q

Carbonation

A

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

11
Q

which rocks are vulnerable to carbonation?

A

Limestone and other carbonate rocks

12
Q

Hydrolysis

A

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

13
Q

Which rocks are vulnerable to hydrolysis?

A

Igneous and metamorphic rocks containing feldspar and other silicate materials

14
Q

Oxidation

A

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

15
Q

Which rocks are vulnerable to oxidation?

A

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

16
Q

Biological weathering

A

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

17
Q

Types of biological weathering

A
  • plant roots

- rock boring

18
Q

Plant roots

A

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

19
Q

Which rocks are vulnerable to plant roots?

A

Vegetated cliff tops, which can contribute to rock fall.

20
Q

Rock boring

A

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

21
Q

Which rocks are vulnerable to rock boring?

A

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

22
Q

How fast is the rate of weathering?

A

It is very slow

23
Q

How does weathering contribute to coastal recession?

A
  • 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.
24
Q

Mass movement

A

the downslope movement of rock and soil.

25
Q

Types of mass movement

A
  • Fall
  • Topple
  • Rotational slides/slumping
  • Flow
26
Q

Fall

A
  • 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
27
Q

Topple

A
  • geological structure influences topples

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

28
Q

Rotational slide/slumping

A
  • 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
29
Q

Flow

A
  • 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
30
Q

What causes a rotational slide/slump?

A
  • 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.