Coastal processes Flashcards
What are the five main ways waves erode the coastline?
Abrasion- Bits of rock and sediment hit against the cliff surface, breaking bits off and smoothing surfaces.
Hydraulic action- Air in the cracks off the cliffs is compressed when waves crash in. The pressure from compressed air breaks off rock pieces.
Wave quarrying- The energy of a wave as it breaks against a cliff is enough to detach bits of rock.
Solution- Soluble rock (limetsone/chalk) get gradually dissolved by sea water.
Attrition- Bits of rock in the water smash against eachother and break into smaller bits.
What are the four main processes of transporting eroded material?
Solution- Substances that ca dissolve are carried along in the water e.g. limestone is dissolved into water thats slightly acidic.
Suspension- Very fine material such as silt, clay particles, is whipped up by the turbulence ajd carried along in the water. Most eroded material is transpoted this way.
Saltation- Lager particles, such as pebbles or gravel are to heavy to be carried in suspension. Instead the force of water causes them to bounce along the sea bed.
Traction- Very large particles e.g. boulders, are pushed along the sea bed by the force of water.
What is longshore drift?
1) Swash carries sediment up the beach, parallel to the prevailing wind. Backwash carries sediment back down the beach, at right angles to the shoreline.
2) Whens theres an angle between the prevailing wind and the shoreline, a few rounds of swash and backwash move the sediment along the shoreline
ZIG ZAG LINE
What is deposition?
Marine and Aeolian
1) Deposition is when material being transported is dropped on the coast:
Marine deposition is when sediment carried by seawater is deposited.
Aeolian dpeosition is when sediemnt carried by wind is deposited.
2) Both marine and aeolian deposition happen when the sediment load exceeds the ability of the water/wind to carry it.
Wind and water slow down for similar reasons:
> friction increases- if waves enter shallow water or wind reaches land, friction between the water/wind and ground surface increases, which slows down the water or wind.
> Flow becomes turbulent- if water or wind encounters an obstacle, flwo becomes rougher and overall speed decreases.
What is sub-aerial weathering?
Sub-aerial weatheirng is the gradual breakdown of rock by agents such as ice, salt, plant roots and acids. Weathering weakens cliffs and make them more vulnerable to erosion.
What is salt weathering?
1) Salt weathering is caused by saline water.
2) This saline water enters pores or cracks in rocks at high tide.
3) As the tides go out the rocks dry and water evaporates, forming salt crystals. As the salt crytals form they expand, exerting pressure on the rock- this causes pieces to fall off.
what is freeze-thaw weathering?
1) Freeze thaw weathering occurs in areas where temperaturs fluctuate above and below freezing.
2) Water enters the joints and crevices in rocks.
3) If the temperature drops below 0 celcius, the water in the cracks freezes and expands.
4) Repeated freeze thaw weakens the rocks.
What is chemical weatheirng?
1) Chemical weathering is the breakdown of rock by changing its chemical composition.
2) For example, carbon dioxide in the atnosphere dissolves in rainwater, forming a weak carbonic acid. This acid reacts with rock that contains calcium carbonate, so the rocks are graually dissolved.
What is mass movement?
Mass movement is the shifting of material downhill due to gravity. In coastal areas, it is most likely to occur when cliffs are undercut by wave action- this causes an unsupported overhande, which is likely to collapse.
Types of mass movement
Slides- material shifts in a stright line
Slumps- material shifs with rotation
Rockfalls- material breaks up and falls
Mudflows- material flows down slope.
