As previously mentioned, waves can be sorted superficially into two branches: destructive and constructive. Also as aforementioned, constructive waves build up beaches and destructive waves take away their material.
Constructive waves have a larger force in their swash than they do in their backwash; this simply means that the power with which they approach a beach is greater than the power with which they retreat. If the sea is carrying a pebble, the pebble will be pushed onto the beach with a greater force than the one that attempts to draw it back, often meaning it is deposited onto the beach- this is how beaches grow. Furthermore, constructive waves can be even further categorised: they have less energy in general than destructive waves; they have less height and frequency than destructive waves (generally being under one metre tall and delivering anywhere between six and ten waves per minute).
On the other hand, destructive waves have a smaller force in their swash than in their backwash; this means that the power with which these waves approach a beach is less that the power with which they retreat. Will you welcome another example? Said pebble from earlier is sat on the beach during a storm, and the swash comes in with a substantial force, but the backwash retreats with an even larger force, taking our pebble back into the sea. In addition, there are also features to a destructive wave: they have more energy is general than constructive waves; they have more height and more frequency than constructive waves (typically exceeding one metre in height and ranging between ten and fourteen waves a minute in frequency). This means that it is usually destructive waves that are the cause of erosion and occur during storms. However, both types of wave can erode beaches- we will get to that in section three.
Our strange obsession with categorising every singe thing under the sun means that the naïve topic of 'Types Of Wave' cannot do justice to the myriad of variants of waves that exist. Nonetheless, important ones shall be mentioned.
Breaking waves can be of various power, but the undertone is that the top half of them collapses when they get within a certain proximity of the shoreline. This causes a crash of water- the breaking of the wave. They are caused when the bottom half of the wave has more friction applied to it by the floor of the seabed than the top half of the wave, meaning the top half proceeds with a greater motion than the lagging bottom. Of course, breaking waves can be subcategorised into many other wave types, but these are not essential for understanding the complexity of the coasts.
The last wave that will actually come into play later on in this book is the tsunami- a name you have likely heard based on the devastation they can cause. Most tsunamis are the result of earthquakes, though some are the product of other massive marine interruptions: volcanic eruptions or landslides. These waves likely are one of the most damaging to the coastline and its people- the dubbed 'Boxing Day Tsunami' of 2004 took 230,000 lives directly and indirectly.
In summary, waves can be constructive and destructive, but are easily broken down into further categories. Other waves types may be touched upon more if it is needed, but for now that is it.
YOU ARE READING
Coasts: An Encyclopaedia
No FicciónCoasts: An Encyclopaedia is a guide to the processes, landforms and alterations that are happening across the most rapidly changing landscapes on the planet. The book will explore the processes in detail, the remarkable features that are created as...
