Topic3(2)- Coastal Processes Flashcards
Six main ways waves erode coast
1) corrasion (abrasion)
2) hydraulic action
3) cavitation
4) wave quarrying
5) solution (corrosion)
6) Attrition
Abrasion (corrasion)
Bits of rock/sediment transported by waves smash and grind against rocks and cliffs, breaking bits off & smoothing surfaces
Hydraulic action
Air in cracks in cliffs is compressed when waves crash in. The pressure exerted by compressed air breaks off rock pieces
Cavitation
As waves recede, the compressed air expands violently, again exerting pressure on the rock causing pieces to break off
Wave quarrying
The energy of a wave as it breaks against a cliff is enough to detach bits of rock
Solution (corrosion)
Soluble rocks (limestone n chalk) get gradually dissolved by the seawater
Attrition
Bits of rock in water smash against each other and break into smaller bits
4 main processes of transportation
- Solution
- Suspension
- Saltation
- Traction
Solution (transportation)
Substances that can be dissolved are carried along in the water e.g limestone in slightly acidic water
Suspension
Very fine material, like silt and clay, is whipped up by turbulence (erratic swirling of water) and carried along in water
Saltation
Larger particles, such as pebbles, are too heavy to be carried via suspension. Instead the force of water causes them to bounce along sea bed
Traction
Very large particles, like boulders, are pushed along sea bed by force of water
Longshore drift
1) Swash carries sediment up the beach, parallel to prevailing wind. Backwash carries sediment down beach at right angles to shoreline
2) when theres an angle between the prevailing wind and the shoreline, a few rounds of swash and backwash move the sediment along coastline
Deposition and its 2 types
When material being transported is dropped on the coast
1) marine deposition - sediment carried by sea water deposited
2) Aeolian deposition- sediment carried by wind deposited
When do Marine and Aeolian deposition happen? And why?
-When the sediment load exceeds the ability of water or wind to carry it
-this can happen due to an increase in sediment load or wind or water flow slows down (less energy)
-
2 reasons wind and water slow down:
1) friction increases (shallow water or wind reaches land, friction slows them down)
2) Flow becomes turbulent (encountering of an obstacle- flow becomes rough and speed decreases)
What happens to waves if wind slows down
Wave height, speed and energy decrease
Sub-aerial weathering
Gradual break down of rock by agents such as ice, salt, plant roots and acids. Weathering weakens cliffs, making them more vulnerable to erosion
4 types of Sub-aerial weathering
1) salt weathering
2) freeze-thaw weathering
3) chemical weathering
4) wetting and drying
Salt weathering
- caused by saline (salty) water
- saline water enters cracks in rocks at high tide
- as tide goes out, rocks dry and water evaporates, forming salt crystals
- the salt crystals expand as they form, exerting pressure on the rock, causing pieces to fall off
Freeze-thaw weathering
- occurs in areas where temperatures fluctuate above and below freezing
- water enters joints and crevices in rocks
- if temp. drops below 0 celcius, water freezes and expands in cracks
- over time, repeated freeze-thaw weakens the rocks and causes pieces to fall off
Chemical weathering
- the breakdown of rock by changing its chemical composition
- e.g. Carbon dioxide in atmosphere dissolves in rainwater, forming a weak carbonic acid. This acid reacts with rock which contains calcium carbonate
Wetting and drying
- some rocks contain clay
- when clay gets wet, it expands and the pressure causes fragments of rock to break off
Mass movement
The shifting of material downhill due to gravity
In coastal areas its most likely to occur when cliffs are undercut by wave action (unsupported overhang causing it to collapse)
4 types of mass movement
1) Slides
2) Slumps
3) Rockfalls
4) Mudflows
Slides
Material shifts in a straight line
Slumps
Material shifts with a rotation
Rockfalls
Material breaks up and falls
Mudflows
Material flows downslope
Factors affecting mass movement
- unconsolidated rocks are prone to collapse as theres little friction between particles to hold them together
- heavy rain, can saturate unconsolidated rock , further reducing friction making it more likely to collapse
- Runoff can erode fine particles and transport them downslope
