COASTAL SYSTEMS AND LANDSCAPES CGP - Coastal Processes Flashcards
What are the two types of processes that affect the coast?
Marine processes caused by the sea. Sub-aerial processes aren’t directly caused by the sea.
Six main ways waves erode the coastline
Corrasion/abrasion Hydraulic action Cavitation Wave quarrying Solution/corrosion Attrition
Corrasion/abrasion (erosion)
Bits of rock and sediment transported by the waves smash and grind against rocks and cliffs, breaking bits off and smoothing surfaces.
Hydraulic action (erosion)
Air in cracks in cliffs is compressed when waves crash in. The pressure exerted by the compressed air breaks off rock pieces.
Cavitation (erosion)
As waves recede, the compressed air expands violently, again exerting pressure on the rock and causing pieces to break off.
Wave quarrying (erosion)
The energy of a wave as it breaks against a cliff is enough to detach bits of rock.
Solution/corrosion (erosion)
Soluble rocks (e.g.limestone, chalk) get gradually dissolved by the seawater.
Attrition (corrosion)
Bits of rock in the water smash against each other and break into smaller bits.
Transportation
The process of eroded material being moved.
What transports eroded material?
Energy provided by waves, tides and currents.
Four main processes of transportation
Solution
Saltation
Suspension
Traction
Solution (transportation)
Substances that can dissolve are carried along in the water. E.g. limestone is dissolved into water that slightly acidic.
Suspension (transportation)
Very fine material, such as silt and clay particles, is whipped up by turbulence (erratic swirling of water) and carried along in the water. Most eroded material is transported this way.
Saltation (transportation)
Larger particles, such as pebbles or gravel, are too heavy to be carried by suspension. Instead, the force of the water causes them to bounce along the sea bed.
Traction (transportation)
Very large particles, e.g. boulders, are pushed along the sea bed by the force of the water.
What is longshore/littoral drift?
The process of sediment being transported along the shore in the direction of the prevailing wind.
Describe longshore drift
Swash carrels sediment (e.g. shingles, pebbles) up the beach, parallel to the prevailing wind. Backwash carries sediment back down the beach, at right angles to the shoreline. When there’s angle between prevailing wind and shoreline, a few rounds of swash and backwash move the sediment along the shoreline.
Deposition is when…
…material being transported is dropped on the coast.
Marine deposition
When sediment carried by seawater is deposited
Aeolian deposition
When sediment carried by wind is deposited
When does both marine and aeolian deposition happen? Why?
When the sediment load exceeds the ability of the water or wind to carry it. Can be because sediment load increases (e.g. if there is landslide), or because wind or water flows slows down (so it has less energy).
Why do wind and water slow down?
Friction increases or flow becomes turbulent
Friction increases (deposition)
If waves enter shallow water or wind reaches land, friction between the water/wind and ground surface increases, which slows down the wind or water.
Flow becomes turbulent (deposition)
If water or wind encounters an obstacle (e.g. a current moving in the opposite direction, or n area of vegetation), flow becomes rougher and overall speed decreases.
What happens if wind drops?
Wave height, speed and energy will decrease.
Sub-aerial weathering
The gradual break down of rock by agents such as ice, salt, plant roots and acids.
What does weathering do to cliffs?
Weakens cliffs and makes them more vulnerable to erosion.
What are the five types of weathering?
Salt weathering Freeze-thaw weathering Chemical weathering Wetting and drying Biological weathering
What is salt weathering caused by? How does it occur?
Saline (salty) water. Saline water enters pores or cracks in rocks at high tide. As tide goes out the rocks dry and the water evaporates, forming salt crystals. As salt crystals form they expand, exerting pressure on the rock - causing pieces to fall off.
Where does freeze-thaw weathering occur?
In areas where temperatures fluctuate above and below freezing.
How does freeze-thaw weathering occur?
Water enters joints and crevices in rocks. If temperature drops below 0 degrees C, water in cracks freezes and expands. Over time, repeated freeze-thaw action weakens the rocks and causes pieces to fall off.
Wetting and drying weathering
Some rocks contain clay. When clay gets wet, it expands and the pressure caused by this breaks fragments off the rock.
What is chemical weathering and example.
The breakdown of rock by changing its chemical composition. E.g. carbon dioxide in atmosphere dissolves in rainwater, forming weak carbonic acid. This acid reacts with rock that contains calcium carbonate - e.g. Carboniferous limestone, so the rocks are gradually dissolved.
Biological weathering and example
Weathering caused by biological organisms e.g. plants, animals, bacteria. E.g. plant roots growing into cracks in the rock and widening them can also cause rocks to break.
What is mass movement?
The shifting of material downhill due to gravity.
When is mass movement most likely to occur in coastal areas?
When cliffs are undercut by wave action - this causes an unsupported overhang, which is likely to collapse.
Types of mass movement
Slides Slumps Rockfall Mudflow Soil creep
Slides (mass movement)
Material shifts in a straight line.
Slumps (mass movement)
Material shifts with a rotation
Rockfalls (mass movement)
Material breaks up and falls
Mudflows
Material flows downslops
Soil creep (mass movement)
Material moves gradually downwards
What are unconsolidated rocks (e.g.) prone to and why?
E.g. clay. Prone to collapse as there’s little friction between particles to hold them together.
What can heavy rain do to unconsolidated rock and what does this result in?
Can saturate unconsolidated rock, further reducing friction and making it more likely to collapse.
How is runoff related to mass movement?
Runoff (flow of water overland) can erode fine particles (e.g. sand and silt) and transport them downslope.
Unconsolidated rock
Minerals or sediments in the form of loose particles, such as sand or gravel.
