Coastal Processes Flashcards
Corrasion/abrasion
Bits of rock and sediment transported by the waves smash and grind against rocks and cliffs, breaking bits off and smoothing surfaces.
Hydraulic action
Air in cracks n cliffs is compressed when waves crash in. The pressure exerted by the compressed air breaks off rock pieces.
Cavitation
As waves erode, the compressed air expands violently, again exerting pressure on the rock and 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
Soluble rocks such as limestone and chalk get gradually dissolved by the sea water.
Attrition
Bits of rock in the water smash against each other and break into smaller bits.
Traction
Traction involves the rolling of large and heavy rocks along the seabed by the force of the water.
Solution
Sediment that has dissolved completely will be transported in solution. For example, limestone is dissolved into water that’s slightly acidic.
Saltation
Particles such as pebbles or gravel are too heavy to be carried in suspension. Instead the force of the water causes them to bounce along the sea bed.
Suspension
Very fine material, such as silt and clay particles, is whipped up by turbulence and carried along in the water. Most eroded material is transported in this way.
Longshore drift
Swash carries sediment up the beach, parallel to the prevailing wind. Backwash carries sediment back down the beach, at right angles to the shore line. When the prevailing wind is at an angle, sediment moves along the shore line.
Marine deposition
When sediment carried by sea water is deposited.
Aelion deposition
When sediment carried by wind is deposited.
Deposition
It occurs when sediment load exceeds the ability of the water or wind to carry it. This is because either sediment load increases (e.g. landslide) or because wind or water flow slows down.
Why might wind and water slow down?
Friction increases; if waves enter shallow water or wind reaches land, friction between the water/wind and ground surface increases.
Flow becomes turbulent; if water or wind encounters an obstacle (e.g. a current moving in the opposite direction, or an area of vegetation), flow becomes rougher and overall speed decreases.
Sub-aerial weathering
The gradual break down of rocks by agents such as ice, salt, plant roots and acids. It weakens cliffs and makes them more vulnerable to erosion.
Salt weathering
Saline water enters pores or cracks in rocks at high tide. As the tide goes out the rocks dry and the water evaporates, forming salt crystals. Crystals expand as they form, exerting pressure on the rock and causes pieces to fall off.
Freeze-thaw weathering
Occurs in areas where temperatures fluctuate above and below freezing. Water enters the joints and crevices in the rocks and freezes and expands as temperatures drop below zero degrees. This weakens rocks over time and eventually pieces fall off.
Wetting and drying
When clay that is present in some rock gets wet, it expands and the pressure caused by this breaks fragments off the rock.
Chemical weathering
Rocks breakdown as their chemical composition changes. For example, CO2 dissolves in rainwater, forming a weak carbonic acid. This acid reacts with rocks that contain CaCO3, so the rocks are gradually dissolved.
Mass movement
The shifting of material down hill due to gravity. In coastal areas, it is more likely to occur when cliffs are undercut by wave action as this causes an unsupported overhang which makes them more likely to collapse.
Conditions increasing the likelihood of mass movement
Unconsolidated rocks such as clay are prone to collapse as there is little friction between particles to hold them together.
Heavy rain can saturate unconsolidated rock, further reducing friction and making it more likely to collapse.
Runoff can erode fine particles and transport them downslope.
Landslides
Material shifts in a straight line.
Slumping
A type of landslide by which material shifts with a rotation.
Rockfalls
Material breaks up and falls.
Mudflows
Material flows downslope.
