Coastal Processes Flashcards
Marine processes
ARE caused by sea
Erosion, transportation and deposition
Sub-aerial processes
Aren’t directly caused by the sea
(Land based)
(Weathering, runoff and mass movement)
Positive Feedback in Weathering
Rate of debris removal exceeds the rate of weathering/mass movements
POSITIVE FEEDBACK as the rate of weathering/mass movement could increase
Negative Feedback in Weathering
Debris removal is slow and ineffective, leads to a build up of debris that reduces the exposure of the cliff face
NEGATIVE FEEDBACK as the weathering/mass movement rate will decrease further
Mass Movement
The downhill movement of weathered material under the force of gravity
When is a mass movement most likely to occur?
When cliffs are undercut by wave action - this causes an unsupported overhang, which is likely to collapse
Types of mass movement?
- Landslides (straight line)
- Slumps (with rotation)
- Rockfalls (breaks up and falls)
- Mudflows (downslope)
- Soil Creep
Landslides
Rate: usually rapid
Wet/Dry: both
Movement: slide
Slumps
Rate: usually rapid
Wet/Dry: both
Movement: slide
Rockfalls
Rate: rapid
Wet/Dry: dry
Movement: fall
Mudflows
Rate: often quite rapid
Wet/Dry: wet
Movement: flow
Soil creep
Rate: imperceptible
Wet/Dry: wet
Movement: creep
Unconsolidated rocks are prone to collapse as there’s little ________ between the _________ to hold them together
Friction
Particles
________ ______ can saturate unconsolidated rock, further reducing ________ and making it more likely to ___________
Heavy rain
Friction
Collapse
________ (the flow of water over the land) can ________ fine particles and transport they downslope
Runoff
Erode
Sub-aerial weathering is the ________ break down of _____ by agents such as…
Gradual
Rock
Ice
Salt
Plant roots
Acids
Weathering…
Weakens cliffs and makes them more vulnerable to erosion
Biological Weathering
The breakdown of rocks by organic activity is biological weathering
Biological weathering (3)
– Plant roots grow into cracks (cracks grow) as roots widen
– Water running through decaying vegetation becomes acidic
– Birds and animals dig burrows into cliffs (puffins and rabbits)
Chemical weathering
Involves a chemical reaction where salts may be dissolved or a claylike deposit may result (easily eroded)
Chemical weathering (3)
– Carbonation (rainwater absorbs C02 = weak carbonic acid) reacts with CaCO to form calcium bicarbonate - easily eroded
– Oxidation (rock minerals - e.g. iron —> rust)
– Solution (Dissolving of rock minerals)
Physical weathering
Involves the break up of rocks without any chemical changes taking place
Physical weathering (3)
– Freeze thaw weathering (water increases in volume by 10%)
– Salt weathering (salty water enters cracks in rock at high tide, water evaporates forming salt crystals which exert pressure on rock as they form)
– Wetting and drying (rocks containing clay expand when wet and this pressure exerted breaks fragments off the rock)
Processes of erosion (6)
Abrasion Hydraulic action Cavitation Wave quarrying Solution Attrition
Hydraulic action
Air in cracks in cliffs is compressed when waves crash in. The pressure exerted breaks up the rock.
Wave quarrying
The energy of a wave as it breaks can detach break off bits of rock.
Abrasion
Material being thrown against the rock by the waves, smoothening surfaces and breaking bits off
Attrition
Bits of rock in the water smash against each other and break into smaller pieces
Solution
Soluble rocks get gradually dissolved by the seawater
Cavitation
As waves recede, the compressed air expands violently, exerting pressure on the rock causing bits to break off.
Some of the many factors that affect the rate of coastal erosion include…
Defences Type of rock Type of coastline Wind direction Vegetation Fetch
Terminal scour
Higher than average rates of erosion at the end of a sea wall/sea management
Transportation processes (4)
Solution
Suspension
Saltation
Traction
Solution
Soluble materials dissolve in the water and are carried along
E.g. limestone is dissolved into water that’s slightly acidic
Suspension
Very fine material like silt and clay is carried in the water. Most eroded material is transported in this way
Saltation
Larger particles, pebbles/gravel, are bounced along the sea bed by the force of the water
Traction
Very large particles, (boulders) are pushed along the sea bed by the force of the water
2 key features which determine transportation process?
Energy & Size
Longshore Drift
The process of sediment being transported along the coastline by the swash (same angle as prevailing wind) and the backwash (90 degrees to sea.)
Swash
Carries sediment UP the beach, parallel to the prevailing wind.
Backwash
Carries sediment back DOWN the beach, at right angles to the shoreline.
Deposition is when…
Material being transported is dropped on the coast
Marine deposition
Sediment carried by the seawater is deposited
Aeolian deposition
Sediment carried by the wind is deposited
High energy coasts
Small particles easily transported whilst larger and heavier material is deposited forming shingle beaches
Low energy
Even the smallest material is deposited forming mudflats and saltmarshes
Deposition occurs when the s___________ l_____ exceeds the ability of the water/load to carry it.
This is due to either:
Sediment load
- Sediment load increases (e.g.landslide)
- Wind/water flow slows down (so it has less energy)
Wind and water slow down due to…
- Friction increasing (water - shallower or wind - land)
- Flow becomes turbulent - obstacle? Flow becomes tougher and overall speed decreases
- Wind drops, wave height, speed and energy will decrease as well
