The formation of headlands and bays
The coastline consisted of parallel bands of hard and soft rock which were perpendicular to the sea. As a result of differential erosion, the bands of soft rock were eroded much more quickly than the bands of resistant rock to form bays and headlands. The headlands will be eroded back as a result of wave refraction. Caves, arches, stacks and stumps will form which will eventually be eroded away. The bays will advance as deposition will take place at their heads to form Bay-head Beaches. Eventually, the coastline will become straight again and the whole process of differential erosion will resume again to result in an irregular coastline.
The major features of the coast
Headland Features
Wave Cut Platforms
Waves
A BEACH PROFILE
This is the shape of the beach. Some beaches may be steeper than others, some may be wider and some may have a short distance between the sea and cliff.
All these differences are a result of how waves break on the beach.
WAVES
If you blow across a glass of water, ripples will form. The same process forms waves at sea (obviously a much bigger wind source! - well, some people have enough I suppose!!).
The size of the waves depends on:
The strength of the wind
How long the wind blows for (time)
The length of water the wind blows over (the FETCH)
Some waves have massive fetches - the coast of Cronwall receives a fetch from Florida - that's about 6000km!
SUMMER WAVES
In the summer, waves are small. They are shorter in height (small amplitude) and there is a larger space between each wave (longer wavelength).
They are called SPILLING or CONSTRUCTIVE waves.
They have:
a strong swash
a gentle backwash
They transport material onto the beach and help make the beach larger by depositing sediment.
WINTER WAVES
In the winter, waves are large. They are taller in height (large amplitude) and come in to shore quicker as there is less space between each wave (shorter wavelength).
They are called PLUNGING or DESTRUCTIVE waves.
They have:
a weak swash
a strong backwash
They erode sand from the beach and take it away into the sea by the rip current (the backwash that travels under the incoming swash). This makes the beach steep and can create an offshore bar
Longshore Drift
The main way sediment is transported is by LONGSHORE DRIFT.
This happens when waves break at an angle to the coast. The swash (the movement of water up the beach) moves diagonally due to the direction of the wind and the backwash (the movement of water down the beach) goes straight back out because of gravity.
This creates a movement along the beach called longshore drift and sediment can be dragged hundreds of miles before being deposited.
Material gets carried along the coast by LONGSHORE DRIFT.
If the coast changes direction (e.g. at a headland) the sediment may get deposited across an open stretch of water (like a river mouth). This is a SPIT. If the wind direction changes the spit may curve at the end.
If the longshore drift does this over a bay it creates a BAR (a huge block of sand) and leaves a LAGOON behind it.
Quick videos showing how a spit may stretch out to an island and create a tombolo and showing how spits, dunes and marshes form using examples from Wales.