What are traveling waves? The famous walls of water so feared by sailors

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abnormal wave
From a scientific point of view, an anomalous wave is defined as a wave that is greater than the height of a significant wave, i.e. the arithmetic mean of the highest waves.
Daniel Ingemi Daniel Ingemi 7 minutes

Apart from the devastation caused by it “tsunami” and from the so-called “rogue waves”, seas and oceans can, under certain conditions, create impressive “walls of water”, sometimes unpredictable, better known as “rogue waves”.

From a scientific point of view an anomalous wave is defined as a wave that is greater than the height of a significant wave, i.e. the arithmetic mean of the highest waves. Unfortunately, very often the term “rogue wave” is mistakenly associated and confused, especially in the journalistic world, with a tsunami.

The difference between wild waves and tsunamis

But in fact, from a scientific point of view, these are two phenomena of different origin and nature.

Tsunamis, unlike anomalous waves, are triggered by violent surface earthquakes that have an epicenter in the sea or in the middle of the ocean, by strong explosive underwater volcanic eruptions, or by colossal underwater landslides (these are the ones that hit the Mediterranean Sea) triggered by volcanic eruptions. or large earthquakes (such as in Messina and Reggio Calabria in 1908).

They also act differently than rogue waves. The displaced water gradually spreads to the surface and creates very long surface waves, even several hundred kilometers, extending over the entire surface of the ocean (like when you throw a stone into a pond).

Different distribution in the ocean

Just to give you some numbers, tsunami waves, when they cross a very large stretch of ocean like the Pacific, they can be around 250-300 kilometers long and reach an impressive speed of propagation, even 600-700 km/h.

waves
Among the most common “anomalous waves” we find the so-called “Sgambetto waves”, also known in some areas of the Mediterranean Sea.

Unlike tsunamis, the dynamics of rogue waves are a bit different. Rogue waves are generated and driven by the interaction of winds, currents and seafloor morphology. Generally, these waves develop in very deep water in the ocean and come from several different directions than the direction of the wind and traditional wave motion.

Where are these waves easy to observe?

Such walls of water, which can exceed 18-20 meters in height, they are also born in those seas where all the elements necessary for their formation are rarely found. Examples include the North Sea, the Mediterranean Sea, or even the North American Great Lakes basin along the border between the United States and southern Canada, where the phenomenon of “constructive interference” or the joining of waves of different origin and direction is relatively rare.

Among the most common “anomalous waves” we find the so-called “Sgambetto Waves”, also known in some areas of the Mediterranean Sea. This type of wave is created when a strong ocean current collides with a series of large, long waves that travel in the opposite direction of the current.

The phenomenon of the cut-off wave

When long waves encounter a strong countercurrent, they tend to slow down their propagation speed. The sea current in the depths acts as a kind of brake that prevents its movement.

This process creates a kind of true “trip” that can lead to surface waves overlapping each other, creating a large giant wave that can reach considerable heights compared to the average wave height at a given time.

Travel waves
The phenomenon of “stripping” is very common off the coast of South East Africa, especially off the coast of East South Africa, where there are strong upwelling sea currents exceeding 5-6 km/h.

The phenomenon of “stripping” is very common off the coast of South East Africa, especially near the coast Eastern South Africawhere there are strong upwelling sea currents exceeding 5-6 km/h. PUSH The “Agulha Current” stands out for its remarkable speed, which can reach a maximum of over 4-5 mph off the coast of eastern South Africa.

Under certain conditions, this strong current, when it meets a series of large waves in the opposite direction, rising from the southern Indian Ocean (raised by strong S-SW and SW storms developing behind the southern cold front), acts as a brake in depth, slows down their propagation speed and creates gigantic, rather steep waves, even more than 5-6 meters high, which may pose a serious threat to maritime navigation in the stretch of ocean off the South African coast.

The churning waves of the Strait of Messina

But a phenomenon “trip” it is also known in the Mediterranean, especially in the area of ​​the Strait of Messina, they are subject to persistent and strong tidal currents that often move against the prevailing wind and wave motion.

Strait of Messina
Archival image of the Strait of Messina as seen from the Calabrian coast.

This happens especially in the Strait of Messina, thanks to the “Venturi effect”, intense southerly winds are channeled, pushing the wave motion up to the central and northern part of the channel, between Reggio Calabria and Messina.

Often meeting the current “decreasing”, which moves from north to south in the opposite direction to southerly winds, these waves are slowed down as they move north and turn into very steep and irregular waves, very difficult to navigate, which can exceed a height of 3-4 meters.



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