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Coastal processes

The British Isles are surrounded by coastline and we are an island nation. The processes operating at the coast therefore have a very big impact upon our Island.
Coasts are dynamic environments that have inputs of sediment and losses of sediment. Indeed, they can be viewed as an open system as they receive sediment from outside of their locality. Coasts are in constant change, and numerous factors can affect our coast such as:

1) The type of wave hitting the coastline (destructive or constructive). Constructive waves have strong swash (the movement of the wave up the beach) and weaker backwash (the movement of a wave and sediment down the beach towards the sea). This builds material up at the landward side of the beach. Destructive waves have weak swash and stronger backwash, this carries material away from the beach and can lead to gentle beach profiles or shapes.
2) The rock type and structure of the coastline - some rocks are stronger than others at resisting wave attack. Igneous rocks such as Granite are much tougher than weak clays which are easily eroded. Jointed rocks such as Limestone and sandstone are susceptible to erosion as waves can attack the joints and bedding planes in the rock.
3) The fetch and prevailing wind operating upon the wave. The fetch is the distance over which the wave has travelled, the longer the fetch the bigger the waves and the more destruction caused. The prevailing wind is the dominant or main wind direction, and determines where the wave strikes on the coastline.
4) The geomorphology or shape of the coast in front of the beach or cliff - if a coastline shelves steeply in front of a cliff or beach waves can break directly on that beach causing more damage. A gently sloping beach profile can result in waves breaking sooner and protection of the coastline.
5) The climate of the area - temperature and rainfall can affect which weathering processes occur.

The major processes operating at the coastline are;
Coastal DEPOSITION - Deposition occurs when wave velocities slow, or when ocean currents slow due to encountering frictional forces such as the sea bed, other counter currents and vegetation. Deposition is simply the laying down of preciously eroded and weathered material. We encounter deposition in slow wave environments such as in bays, where contrasting sea currents or river currents slow water down, and why there are low winds (and hence low wave velocities).

Mass movement - Once weakened by weathering mass movement can then deliver this material to beaches and the sea to be eroded. Some mass movement processes occur slowly, such as soil creep and solifluction, but some are very rapid such as rock falls.

Ln
Landslides occur where layers of rock dip towards the sea, and whole blocks of land slips down towards the sea. Slumping occurs in areas with alternating layers of permeable and impermeable rock.

Rotational Cliff Slumping

Erosion
This is the wearing away of the land by moving agents such as the sea. There are several types operating at the coast including: 

  • Hydraulic Power - this is where water from a wave enters cracks in the cliff face, compresses air within the cracks and causes pressure to be exerted on the surrounding rock, which weakens and breaks off.
  • Corrosion - weak acids within the sea can react with certain rocks types at the coast and cause them to dissolve slowly, this is particularly important for Limestone and chalk coastlines.
  • Abrasion - This is where rocks picked up and carried within waves are thrown onto the beach and cliffs
  • Attrition - This is where rocks and pebbles carried within the sea hit against one another and break down into smaller particles.

Weathering  

This is the breakdown of rocks INSITU. This means that the rock structure is weakened by elements of the weather but the rocks remain where they are. There are 2 basic types:

  1. Mechanical -  Weathering processes that cause physical disintegration or break up of exposed rock without any change in the chemical composition of the rock, for instance freeze thaw. This is one process where water enters cracks, freezes (often overnight), expands by 9.05% and exerts pressure on the rock, weakening it.
  2. Chemical - this involve the chemical alteration of the structure of rocks, processes include carbonation (were weak carbonic acids attack rocks) and hydration (where water swells the structure of rock)
    FreezeThaw
Coastal TRANSPORT

This is the movement of material along a coastline. Sediment can be moved by 4 basic processes:

Traction - where large stones are rolled along the sea bed
Saltation - where stones are bounced along the sea bed in a hopping motion
Suspension - where fine material is held within the water mass
Solution - where rocks and minerals are dissolved within the water.

 

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