causes/ effects of subaerial processes (2.B6)

Question 1

types of subaerial processes

Answer 1

1. weathering: the breakdown of rock in situ at or near the surface of the Earth, most active in the source zone of the sediment cell.
2. mass movement: occurs when the downslope gravitational force exceeds the resisting forces of friction and internal rock cohesion.

Question 2

weathering

Answer 2

weakens rock making it more vulnerable to mass movement and cliff retreat… the three types:

1. physical
   EG
   - freeze thaw (water seeps into cracks and freezes increasing volume by 10% widening crack, process repeats)
   - salt crystal growth (less force than freeze thaw: sea water penetrates small cracks in rock at high tide, process continues until high pressure is reached eventually breaking angular fragments of rock away)
   - wetting and drying (rocks containing clay minerals: at high tide theyre soaked and expand, at low tide they dry and shrink, these repeated cycles cause the rock to fragment and crumble)

2. chemical 
EG
- carbonation ( CO2 from cool seawater/ rain reacts with rock w. calcium carbonate eg limestone)
- hydrolysis 
- oxidation 

3. biological 
EG 
- tree root (self explanitory)
- rock boring (eg clams bore into rock and live in them for protection)
- seaweed acid

Question 3

types of mass movement

Answer 3

1. rockfall: large block of rock falls away from cliff as a single piece due to jointing of the rock
   - most likely to occur on steeper jointed cliffs that are exposed to physical weathering
   - often leaves a scree slope at botom of cliff
2. slides: slab of rock can slide over underlying rocks along a slide or slip plane.
   - rocks that are jointed/ have bedding planes parallel to cliff surfice are susceptible to landslides. increase in the amount of water can reduce friction increasing slides.
3. slumps: difference to slides is that there is a rotational movement
   - common where softer materials overline more resistant rock
   - slumping causes rotational scars and more likely to occur in saturated conditions
   - repeated slumping= terraced cliff profile
4. soil creep: slow downhill movement of individual soil particles
   - slowest form of mass movement and is almost continuous
5. solifluction: top layer of soil thaws in summer but the layer below remains frozen
   - avegerages between 5cm and 1m every year
6. mudflows: increase of heavy water reduces friction causing earth to flow over underlying bedrock
   - difference between slide and flow is that in a slide the material remains intact but in a flow the material becomes jumbled up.
   - leaves behind a lobe

Question 4

factors influencing mass movement

Answer 4

• angle of slope/ cliff
• the rock type and its structure
• vegetation cover
• how wet the ground is