Coasts

WAVES

Waves are eliptical or circular movements of water near the surface of the sea.  They are composed of crests and troughs.  Waves are the main source of energy along the coast.

Waves are formed by the friction of the wind blowing over the surface of the sea.  In deep water out to sea, the water particles are in circular orbit.  As the water becomes shallower near the shore, the circular orbit becomes flattened.  The bottom of the wave is slowed down by friction with the sea bed, so the top of the wave moves faster than the bottom.  This causes the wave to collapse and break.

The size and energy of a wave is affected by these factors:

• Wind velocity
• Duration for which the wind blows
• The size of the fetch - the area of open water over which the wind can blow
• The depth

The swash is the movement of water up the beach due to the energy of the wave.  The backwash is the movement of water down the beach due to gravity.

Constructive waves are formed when the force of the swash is greater than the force of the backwash.  The gradient of the beach is gentle, so the waves break gently and spill up the beach.  The swash pushes beach material up the beach, making the gradient steeper. The backwash soaks into the sand.  The gentle gradient means that gravity has less impact.  The wave frequency is low.

Destructive waves are formed when the force of the backwash is greater than the force of the swash.  The gradient of the beach is steep, so the waves break violently and plunge downwards.  There is a strong backwash due to the steep slope and gravity, so the backwash pulls material down the beach, making the gradient less steep.  The frequency of destructive waves is high.

COASTAL PROCESSES

Erosion is the wearing away and removal of rocks by rivers, glaciers, waves or the wind.

There are four erosional processes:

• Hydraulic action - where the force of the water pushes air into cracks in the rocks and pulls material away
• Abrasion - particles of different sizes collide with the cliffs and bash material away
• Solution - certain rocks are dissolved by the slightly acidic sea water (eg chalk, limestone)
• Attrition - particles in the sea collide with each other, making each other rounder and smaller

Attrition does not affect the cliff face.

Weathering is the breakdown and weakening of rock where it is.

Mechanical weathering is the breakdown of rock into smaller parts.  There is no chemical change in the structure of the rock.  Freeze thaw is an example of mechanical weathering.  Meltwater runs into cracks in rocks and freezes in the cold weather.  The water therefore expands, making the cracks wider.  When the water thaws, the pressure is released.

Salt weathering is the process of porous…