The waves appear to move in groups because they are generated by wave trains, each having a slightly different period. This phenomenon creates the illusion that the waves are moving together.
When the wind blows across the surface of the sea, it creates friction that generates small ripples. These ripples gradually grow by absorbing the energy of the wind. Some waves capture more energy than others, move ahead, and begin to organize together. This gives rise to what are known as wave trains, groups of waves that travel together over long distances. The waves at the front of the group gradually lose energy, while those at the back gain it. As a result, the waves seem to constantly replace one another within the group, without the overall shape really changing. This phenomenon is particularly noticeable during long swells that traverse an entire ocean while maintaining this grouped organization.
When the wind creates waves on the open sea, each has its own wavelength, which directly influences its speed. This phenomenon is called dispersion: the longer waves, usually the biggest, speed ahead because they move much faster. The smaller waves struggle to keep up and lag behind. As a result, as they advance, the waves sort themselves out, grouping together by similar sizes, and form those famous sets that we observe from the shore. This mechanism explains why we often see a beautiful series of big waves followed by calmer periods.
When two waves meet, they can sometimes merge or partially cancel each other out: this is called interference. Specifically, if two wave crests overlap at just the right moment, it results in a taller wave (constructive interference). Conversely, when a crest meets a trough exactly at the same instant, they partially neutralize each other and create a less powerful wave (destructive interference). It is this interference effect between several waves arriving simultaneously that creates the characteristic groups visible to the naked eye, with series of large waves separated by calmer series. This is called wave trains. You can even feel this phenomenon when you swim or surf: calm moments alternate with series of big waves, then back to calm.
The strength, duration, and size of the wind zone directly influence wave behavior. A strong and consistent wind over a large distance produces longer and more organized wave sets. In contrast, light or variable winds lead to short, irregular, and chaotic waves. Distant storms can also create regular swells that travel to our shores, potentially surprising swimmers with their alternating rhythm of large waves and calmer periods. Even when the weather is nice at home, a distant storm out at sea can shape the profile of the waves observed on the beach.
When the waves approach the shore, the seafloor becomes shallower—and it disrupts everything. As a submerged relief approaches, the waves slow down, gain height, and become narrower. This change primarily affects the waves closest to the coast, creating natural clusters with areas where the waves intensify and others that are calmer. The shallower the depth, the stronger this accumulation and slowing phenomenon. The submarine relief (sandbars, reefs, submerged rocks) also guides the waves and enhances their grouping by creating specific areas of wave amplification visible from the beach.
The phenomenon of rogue waves, also known as monstrous waves or abnormal waves, is often related to constructive interference phenomena, which occur when at least two wave systems meet.
Contrary to what one might think, the water particles themselves hardly move horizontally with the waves; they primarily perform a circular motion in place.
The seabed can strongly influence the shape of a wave: a gentle slope will promote a regular, progressive wave, while a steep slope can create hollow and fast waves, which are highly favored by surfers.
The waves observed on the coasts generally do not originate nearby. They are often generated by storms located hundreds or even thousands of kilometers offshore.
As the waves encounter shallow waters, the seabed alters their speed, wavelength, and height. These changes in depth shape the regularity and coherence of wave groups, sometimes concentrating their energy and increasing their amplitude in specific areas.
No. In fact, each individual wave in a group generally moves faster than the group itself. The speed of the group (called group velocity) differs from the speed of individual waves (phase velocity), which creates the impression that the waves are forming at the back of the group and weakening at the front.
Sure! Here’s the translation: "Yes. Strong or irregular winds can alter the regularity, height, and spacing between waves, thereby influencing their behavior in groups. Rapid changes in wind often create irregular or fragmented groups."
Surfers generally wait for the most consistent and powerful sets or groups of waves. These sets provide them with more energy, more stable conditions, and better-defined waves that facilitate maneuvers and enhance their overall experience.
Within a group or train of waves, constructive and destructive interferences cause the amplitude of the waves to vary. Some waves thus become taller when several waves converge in phase, increasing their size.
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