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According to the CSEC Syllabus, the specific objectives related to Coastal Processes are as follows:
Describe wave processes
Explain the formation of coastal landforms
As such, we will follow these objectives for this unit.
The Creation of waves
The Creation of waves
Definition: Waves are most commonly formed by friction as the wind blows over the surface of the sea. They can also be formed by earthquakes, volcanic eruptions or underwater landslides. These events though rare, can end up causing a tsunami.
What causes waves to break?
Since we understand that waves are created by friction caused by winds blowing over the water (this is definitely physics at work), we need to know how the friction stops, causing the waves we see when we're at the beach. So here's the process:
As the sea gets near the shore, the circulation rotation of the waves underneath is disrupted due to the shallow and presence of the seabed.
The water motion becomes more elliptical (oval shaped)
The waves grow in varying height dependent on several factors leading to the strength of the wave (energy), and begins to topple forward
Eventually the wave breaks on the shore and water moves up the beach as swash and retreats/drains back down the beach as backwash.
So what are these factors that influence the power of the waves? As the waves approach the coastal area, several factors influencing its power include the following:
Distance of open water over which the wind has blown - Much like an airport runway where planes need to get up to a certain speed to take off, the distance of open water forms what is called a fetch. The longer the fetch, the more powerful the wave as it approaches the coast. This is because it picks up energy as it moves.
Strength of the wind - The stronger the wind, the more powerful the waves. This is because more friction is created dependent on the strength of the wind.
Duration of the wind - If strong winds have blown over a long period of time, this will result in powerful waves. Given that the waves have the propelling force of the wind consistently, they will have a source to gain more energy in the long run.
Presence of obstacles in the water - Whilst the wind influences the energy through which waves gather and move, the presence of coral reefs close to the surface would disrupt the circular rotation thus weakening the wave.
Diagram of Waves approaching the Coast (Taken from CSEC Study Guide pg 76)
Types of waves
There are effectively two different types of waves and they are as follows:
Constructive Waves - these waves are low (smaller in height) but powerful waves that have a strong swash (water surging up the beach after breaking) that pushes material up the beach thus helping to build up the coastal area. These waves have a weak backwash (waves retreating back to sea) thus having little erosion as the force is not strong enough to drag materials back to sea.
Constructive waves are created by storms or strong winds miles away from the coast. These waves travel fast across the ocean transporting material to the top of the beach.
Diagram of a Constructive Wave (Taken from CSEC Study Guide pg 77)
Destructive Waves - Unlike Constructive waves, destructive waves are taller in height and tend to crash down on the beach instead of surging that leads to a cutting effect into the coastline area. Destructive waves have little swash but the backwash is extremely powerful leading to erosion of the lower beach. Destructive waves are usually formed during local storms that are centered close to the coast.
Diagram showing the formation of Destructive Waves
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