Offshore, the wind can blow over large expanses of water, allowing waves to form and disperse, resulting in a calmer sea. Near the coast, the effect of topography and land obstacles limits the dispersion of waves, leading to rough seas.
When waves travel in deep water, they move without being really hindered, as the depths are often very deep. The wave transfers its energy without losing much speed: it remains regular, long, and therefore quite calm. As it approaches the shore, the depth decreases and the water becomes shallower. There, the bottom of the wave gradually rubs against the seabed, which slows down the entire wave, reducing the speed of the bottom while the top continues to move forward. The result: the wave grows, becomes unstable, and can even break, producing foam. This phenomenon called swell explains why shallow areas near the coast often have a choppy sea, while far from the shore, over deep waters, it seems much more peaceful.
The wind blowing at the surface of the water generates waves through friction: in a way, it "grabs" the surface of the sea, causing the water to move. The longer this phenomenon lasts or the greater the distance, the larger the waves become. Offshore, the steady wind eventually creates long waves that propagate easily and remain organized. Near the coast, it's different: the wind loses its regularity and strength, it irregularly grabs the surface of the water, and these irregularities break the rhythm a bit, making the waves more disorderly and shorter. As a result, they appear more agitated. Also, far from land, without obstacles, the waves propagate quietly while slowly losing their energy, whereas close to shore, they constantly collide with irregularities of the seabed and coastline, increasing their agitation.
Near the coast, the seabed changes abruptly: it rises sharply. This forces the waves to slow down and compress upon themselves: as a result, they grow larger and become steeper. When the water is very shallow, like at beaches or reefs, this amplifies the phenomenon, and the waves are stronger and more breaking upon arrival. Conversely, a gentle slope of the seabed, without sudden changes, creates calmer and more regular waves. The rugged shapes of the coastline (cliffs, capes, creeks) also add to the turbulence: they deflect, concentrate, and sometimes even reflect the waves, causing very turbulent zones where currents and chop multiply.
Ocean currents play a significant role in the state of the sea. Offshore, regular, deep, and stable currents like the Gulf Stream mitigate wave formation by carrying wave energy over long distances and gradually spreading it out. Closer to shore, fast local currents abruptly alter the natural movement of waves, often causing visible turbulence and chop. The same idea applies to tides: offshore, they go almost unnoticed, while approaching the coast and in shallow areas, they create significant water movements, generate powerful currents, and markedly increase maritime agitation.
The open ocean waves, as impressive as they may seem, generally subside when they enter the shallow waters near the shore, but their height then significantly increases, which explains the characteristic 'breaking' phenomenon highly sought after by surfers.
The standard measure of wave height is called 'significant wave height,' which corresponds to the average of the highest third of the waves observed over a given period. It is used by sailors and meteorologists to predict sea conditions.
Tsunamis are not caused by wind, but by sudden movements of the ocean floor, typically an underwater earthquake or a landslide. These waves can travel at speeds exceeding 700 km/h offshore.
In maritime navigation, a 'cross sea' refers to the meeting of two wave systems coming from different directions, creating a particularly choppy and potentially dangerous sea for vessels.
Yes, certain highly protected areas such as deep bays, fjords, or regions located behind natural barriers (reefs, islands) can remain relatively calm, even under the influence of strong winds, due to the reduction of fetch and topographic protection.
The crashing of waves occurs when their base slows down upon contact with a shallow seabed while their crest continues moving forward. This phenomenon, being related to shallow depth, is common near the shore and rare in deep waters where the seabed is deep.
Yes, ocean currents can either amplify or dampen waves depending on their direction and intensity. Currents opposing the waves can increase their amplitude, while parallel or weak currents will have little noticeable effect on them.
The longer, stronger, and more distant the wind blows (known as 'fetch'), the more energy, size, and power the resulting waves gain. This is why, in the case of prolonged strong winds, the waves can reach significant heights.
Near the coast, the sea floor rises rapidly toward the surface, reducing the depth. This phenomenon compresses the energy of the waves, causing them to slow down and then swell in height, making them more visible and turbulent near the shore.
No one has answered this quiz yet, be the first!' :-)
Question 1/5
