Coastal
Landscapes
and Change
Enquiry Question 2: How do characteristic coastal landforms
contribute to coastal landscapes?
,2B.4 Marine erosion creates distinctive coastal landforms and contributes to costal
landscapes.
Waves are caused by the friction between wind and water. They are extremely important
along any stretch of the coast as they directly influence the three marine processes of
erosion, transport and deposition.
Wave size and strength depends on:
The strength of the wind
The length of the the wind blows for
Water depth
Wave fetch
In open water out at sea, waves are simply energy moving through water. There is some
circular or orbital water particle motion within the wave, but no forward particle motion.
As waves approach the shoreline, the water shallows and the wave shape changes. At a
water depth of about half the wave length, the orbital motion of the wave touches the
seabed. This creates friction which slows down the wave. The wave length decreases and
wave height increases, so the waves bunch together.
Waves break in shallow water because the crest of the wave begins to move forward faster
than the wave trough which experiences significant friction with the seabed. Eventually the
wave crest outruns the trough and the wave topples forward - a breaker.
As the wave breaks, the water flows up the beach as the swash. The water then runs back
down the beach as the backwash, meeting the next oncoming wave.
The gravitational attraction of the moon causes the oceans to bulge out in the direction of
the moon. Another bulge occurs on the opposite side, since the Earth is also being pulled
towards the moon (and away from the water in the far side). Since the Earth is rotating
while this is happening, two tides occur each day.
If storms occur at the same time as spring tides (the highest high tides), storm surges can
occur when the sea can cause severe coastal erosion and flood low lying coastal areas, eg:
North Sea storm surge of December 2013.
, Constructive Waves Destructive Waves
Low frequency High frequency
Low energy High energy
Weak backwash Strong backwash
Strong swash Weak swash
More depositional More erosive
More dominant in summer More dominant in winter
The dynamic equilibrium of the beach (inputs and outputs are in balance and the beach is in
a stable state) can be upset by the changing weather and therefore wave type. This can
create negative and positive feedback.
In summer, constructive waves build up steep beaches (in equilibrium).
Winter storms upset the equilibrium.
Constructive waves replaced by destructive waves (high energy).
Destructive waves (strong backwash) erode sediment from the beach and move it to
the lower beach. Offshore bar formed.
Lower beach angle reduces wave steepness and the waves become more
constructive.
The cycle repeats.
Beach morphology (the shape of a beach, including its width and slope and features such as
berms and ridges and includes the type of sediment (single, sand, mud)) is strongly
influenced by the nature of the prevailing waves. But wave conditions can fluctuate over
time and bring with them changes to beach morphology. There are four diagnostic beach
features of prevailing wave conditions:
Storm beach: the result of constructive waves and high energy deposition during
stormy weather.
Berms: small ridges built by constructive waves during relatively calm weather.
Landscapes
and Change
Enquiry Question 2: How do characteristic coastal landforms
contribute to coastal landscapes?
,2B.4 Marine erosion creates distinctive coastal landforms and contributes to costal
landscapes.
Waves are caused by the friction between wind and water. They are extremely important
along any stretch of the coast as they directly influence the three marine processes of
erosion, transport and deposition.
Wave size and strength depends on:
The strength of the wind
The length of the the wind blows for
Water depth
Wave fetch
In open water out at sea, waves are simply energy moving through water. There is some
circular or orbital water particle motion within the wave, but no forward particle motion.
As waves approach the shoreline, the water shallows and the wave shape changes. At a
water depth of about half the wave length, the orbital motion of the wave touches the
seabed. This creates friction which slows down the wave. The wave length decreases and
wave height increases, so the waves bunch together.
Waves break in shallow water because the crest of the wave begins to move forward faster
than the wave trough which experiences significant friction with the seabed. Eventually the
wave crest outruns the trough and the wave topples forward - a breaker.
As the wave breaks, the water flows up the beach as the swash. The water then runs back
down the beach as the backwash, meeting the next oncoming wave.
The gravitational attraction of the moon causes the oceans to bulge out in the direction of
the moon. Another bulge occurs on the opposite side, since the Earth is also being pulled
towards the moon (and away from the water in the far side). Since the Earth is rotating
while this is happening, two tides occur each day.
If storms occur at the same time as spring tides (the highest high tides), storm surges can
occur when the sea can cause severe coastal erosion and flood low lying coastal areas, eg:
North Sea storm surge of December 2013.
, Constructive Waves Destructive Waves
Low frequency High frequency
Low energy High energy
Weak backwash Strong backwash
Strong swash Weak swash
More depositional More erosive
More dominant in summer More dominant in winter
The dynamic equilibrium of the beach (inputs and outputs are in balance and the beach is in
a stable state) can be upset by the changing weather and therefore wave type. This can
create negative and positive feedback.
In summer, constructive waves build up steep beaches (in equilibrium).
Winter storms upset the equilibrium.
Constructive waves replaced by destructive waves (high energy).
Destructive waves (strong backwash) erode sediment from the beach and move it to
the lower beach. Offshore bar formed.
Lower beach angle reduces wave steepness and the waves become more
constructive.
The cycle repeats.
Beach morphology (the shape of a beach, including its width and slope and features such as
berms and ridges and includes the type of sediment (single, sand, mud)) is strongly
influenced by the nature of the prevailing waves. But wave conditions can fluctuate over
time and bring with them changes to beach morphology. There are four diagnostic beach
features of prevailing wave conditions:
Storm beach: the result of constructive waves and high energy deposition during
stormy weather.
Berms: small ridges built by constructive waves during relatively calm weather.
