Coastal processes (from GCSE)

 

Depositional lanforms 

Spits, bars, dunes and tombolos are all formed by deposition. Depositional processes include long shore drift and swash.

Transportation

You can see transportation takes place if a beach has groins. Groins are used to slow down or stop long shore drift.

Erosion

Hydraulic action is the name given to erosion which is caused by the force of the waves against rocks and cliffs. This process takes the form of the sea's waves crashing against rocks and cliffs. Water drives air into cracks in the rock, pressure builds up, exploding the crack and forcing bits of rock break off. The stronger the wave, the greater its explosive power.

Corrosion (solution) is an example of a chemical process. Chemicals in the sea water, such as salt dissolve minerals in the rocks, causing them to slowly break up. Sea water can also contain mild acids which have a similar effect. Chemicals released into the sea as a result of pollution can speed up the rate of corrosion.

Attrition are Fragments of rock which have broken off the cliff face fall down and can collect on the seabed. Here, moved by the water, they knock against each other and the bedrock, becoming ever smaller, rounder and smoother.

Corrasion is another physical process which wears down coastal cliffs and rock faces. Waves carry debris (such as sand, shingle and pebbles) which is hurled against the coastline. The debris rubs against the rock and eventually causes pieces to break off. These broken fragments are in turn thrown back at the rock face by the waves and the process repeats itself.

Weathering

Freeze thaw action is an example of physical weathering. Water from rain and from the sea makes its way into cracks in the rock. In cold conditions this water freezes, slightly increasing in volume. The expansion of the ice puts pressure on the rock and causes cracks to open a little. When it thaws, the ice melts and changes back to water. Repeated freezing and thawing weakens the rock and splits it into jagged pieces. These pieces may fall by gravity onto the beach to be broken down further. Bare, exposed cliffs are often subjected to this type of weathering.

Chemical weathering the action of water on rock can cause chemical weathering. Ordinary rainwater contains small amounts of acid. This acidic solution attacks the structure of the rock, causing it to rot and crumble. The rate at which chemical weathering occurs depends on several factors. The acidity of the rainfall affects the rate of weathering. Raindrops naturally absorb carbon dioxide from the atmosphere, resulting in the formation of a very weak acid. However, acid rain caused by pollution (particularly the emission into the atmosphere of sulphur dioxide and nitrogen oxides) is often more damaging, speeding up the rate of destruction caused by chemical weathering. The type of rock is important. Permeable rocks such as limestone and sandstone allow water to penetrate beyond the surface. They are broken down more quickly than impermeable rocks such as slate and granite.

Slumping Waves form as a result of the transfer of energy. They are caused by the friction that occurs when wind blows over water – this friction causes the water to move in a circular orbit. The amount of energy gained by the wave is determined by several factors. These include: the speed of the wind, the length of time that the wind has been blowing, and the distance of open water over which the wind has been blowing – this distance is known as the fetch. These factors will influence the way in which waves behave and the effect they have on the coastline.

Mass movement

 

Rockfall is the rapid, free-fall of rock from a steep cliff face. Rock fragments fall from the face of the cliff because of the action of gravity. This is made worse by freeze-thaw action loosening the rock. Bare, well-jointed rock is very vulnerable to rockfall - water enters the joint, freezes and expands, cracking the rock. A scree slope of fallen rock is formed at the bottom of the cliff.

Mudflow occurs on steep slopes over 10°. It's a rapid sudden movement which occurs after periods of heavy rain. When there is not enough vegetation to hold the soil in place, saturated soil flows over impermeable sub soil, causing great devastation and endangering lives.

Landslips or land slumps are occasional, rapid movements of a mass of earth or rock sliding along a concave plane. They can occur after periods of heavy rain, when the water saturates overlying rock, making it heavy and liable to slide. Undercutting of a steep slope by river or sea erosion weakens the rock above, also making a slump likely.

 

Soil creep is a very slow movement, occurring on very gentle slopes because of the way soil particles repeatedly expand and contract in wet and dry periods. When wet, soil particles increase in size and weight, and expand at right angles. When the soil dries out, it contracts vertically. As a result, the soil slowly moves downslope.