Des scientifiques ont récemment enregistré la vague scélérate la plus folle jamais observée — c'était comme un immeuble de 10 étages surgissant de nulle part au milieu de l'océan. Ces vagues sont rares et imprévisibles, apparaissant soudainement et dominant largement la mer environnante. Cette vague particulière mesurait 58 pieds de haut, environ trois fois plus haute que les vagues qui l'entouraient, et c'est maintenant la plus extrême jamais mesurée officiellement. Les scientifiques étudient les vagues scélérates car elles sont extrêmement dangereuses pour les navires et les plateformes pétrolières, souvent frappant sans avertissement. Grâce à de meilleures technologies et données, les chercheurs se rapprochent de la compréhension de la formation de ces vagues monstres. Le but ultime ? Trouver des moyens de les prédire et de rendre les gens plus en sécurité en mer. Animation créée par Sympa.
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FunTranscript
00:00A four-story water wall, which only rises once every 1,300 years,
00:04has been recorded off the west coast of Canada.
00:07Some attribute to this type of wave the disappearances in the Bermuda Triangle.
00:12Accelerated waves can be powerful enough to make containers and oil platforms sink.
00:18This Canadian aquatic monster has not hurt anyone, but it has made a sensation.
00:22And it seems that we are about to see even higher and more powerful accelerated waves in the future.
00:29The Marine Labs team, the company that owns the buoy that was caught in the Bermuda Triangle wave,
00:34had a hard time believing the data collected.
00:36A huge force emerged from nowhere, pulled the buoy down,
00:40then brought it back to the top, before taking it even further.
00:44Thinking it was an accelerated wave,
00:46they sent the data to a scientist at the University of Victoria, a specialist in the field.
00:52He analyzed them and confirmed that it was not a technical error.
00:56The wave has officially become the most extreme accelerated wave ever recorded.
01:02It was three times higher than all the waves around it.
01:05For centuries, sailors reported seeing giant waves emerge from nowhere,
01:10but no one really believed them.
01:12In 1826, a French marine scientist and officer crossed the Indian Ocean aboard his ship, the Astrolabe.
01:20During a terrible storm, he saw several waves more than 30 meters high,
01:24almost the height of a ten-story building.
01:28The crew of the ship lost one of its members,
01:30but the remaining four people, including the captain, were able to regain the firm ground to tell their experience.
01:37At the time, scientists were hardly convinced that the waves could not go beyond 9 meters high.
01:42Everyone considered that their story was not standing up.
01:45And yet, more than a century later, the cargo ship MS Munchen mysteriously disappeared.
01:51People thought it was insubstantial, just like the Titanic.
01:55And so it was a real shock to learn that there was only one lifeboat left.
02:00When the experts analyzed the damage, they concluded that it must have been hit by a wave about 20 meters high.
02:06Witnesses have told many other stories of giant waves emerging from nowhere,
02:11but scientists have officially recognized the first accelerated wave only in 1995.
02:16It entered history under the name of the Draupner wave, or New Year's wave.
02:21This northern sea monster, 25.6 meters high, hit the Norwegian gas platform Draupner on New Year's Day.
02:30It was twice as big as the waves around it.
02:33The platform had been built to resist waves 19 meters high and had the most advanced sensors of the time.
02:41But the wave did not look like anything we had studied before.
02:45So they had to admit that accelerated waves did exist, and they gave them an official definition.
02:52It is a wave more than twice as high as the one around it.
02:55It can arise at the speed of light in an agitated sea, or appear without warning in calm waters.
03:02These waves have abrupt flanks and a deep hollow below,
03:07and they look like a wall of water emerging from the surface of the sea.
03:11They are so powerful that they can swallow lifeboats.
03:16In 2007, the National Oceanic and Atmospheric Administration
03:20submitted a list of 50 historical maritime tragedies that were most likely caused by accelerated waves.
03:27Some of the events on the list did not occur in the middle of the sea, but in lakes.
03:32The Upper Lake presents a phenomenon known as the Three Sisters.
03:36It is a series of three large waves, one after the other.
03:39The second wave covers the ships' decks before the first one disappears.
03:44The third wave sinks into the gap and adds more water.
03:48These Three Sisters completely overload the boats.
03:51According to a theory, this phenomenon caused the shipwreck of the Edmund Fitzgerald cargo ship in 1975.
03:58Two main theories aim to explain the phenomenon of accelerated waves.
04:03The first is the theory of linear addition.
04:06Imagine waves moving in the ocean at their own speed.
04:10When these waves cross, they come together and become stronger,
04:14which gives birth to an accelerated wave.
04:17Then there is the theory of non-linear focalization.
04:20According to this theory, some waves form groups,
04:24and in this way, they exchange energy.
04:27Sometimes, this exchange of energy gives rise to an accelerated wave.
04:31To predict the formation of these strange waves,
04:34scientists would need an innovative radar system
04:37capable of constantly monitoring the waves near the boats.
04:42They would collect all the data and integrate it into a mathematical model
04:46that would create a real-time image of the ocean surface.
04:50The model would perform new calculations every five minutes.
04:54Thus, the crew could know if extreme waves are preparing to attack them.
04:58Such a system does not exist yet,
05:01but considerable progress has been made in this direction.
05:04Scientists from the University of Melbourne went on an expedition to Antarctica
05:09and discovered that violent winds played an important role in the formation of accelerated waves.
05:14Apparently, they would result from a mixture of violent winds
05:18and the random movement of the waves that interact with each other.
05:22This idea was first tested in a laboratory,
05:25before being confirmed in real situations,
05:27that is, in the oceans.
05:29To study these waves, scientists used 3D cameras.
05:33These cameras work like human eyes,
05:36taking many consecutive images
05:38and thus creating a 3D image of the ocean surface.
05:42The study has shown that accelerated waves
05:45occur more often when the waves are young,
05:48in other words, when they are just starting to form
05:51and are more influenced by the wind.
05:53When strong winds blow on the rising swell,
05:56they reinforce it, raise it, and make it accelerate in an inhomogeneous way.
06:01And some waves come to steal the energy of the neighboring waves,
06:04and they then grow considerably,
06:07turning into accelerated waves.
06:09Scientists noticed that these giant waves
06:11occurred about once every six hours.
06:14They did not record any accelerated waves in quieter seas,
06:18where the wind does not have as much influence.
06:20Scientists fear that accelerated waves
06:23will no longer occur more often in the future,
06:25because the atmosphere and the oceans still contain more energy.
06:29And it seems that these waves can become
06:31much more powerful than we had imagined.
06:34These researchers managed to recreate the famous
06:37Dropner wave in a laboratory for the first time in 2018.
06:41This allowed them to study these mysterious waves closely
06:44and to show that their secret lies in the way they form.
06:48We like to contemplate the quiet waves of the seaside,
06:51but the studied phenomenon occurs offshore,
06:54when waves from different directions meet.
06:57When this happens, the water is pushed upwards,
07:00which creates what is called a partially stationary or transversal wave.
07:04This phenomenon can occur at the junction of two seas,
07:07or when the direction of the wind suddenly changes,
07:10like during a hurricane.
07:11The study has shown that the greater the angle between the waves,
07:14the higher the transversal wave.
07:16Normally, when a wave breaks, it forms a white and spiky peak,
07:20and then it stops growing.
07:22But if a wave is formed with water from several directions,
07:25it can continue to grow even after breaking.
07:28These particular waves can reach a height
07:31twice as high when breaking.
07:34They are then already much more imposing than the so-called normal waves.
07:37And if we add all the power of the waves that meet like this,
07:42we get an object four times higher than what we are used to.
07:45This discovery could change the way we build our wind turbines
07:50and our oil platforms in the ocean,
07:52in order to make them safer.
07:54At present, many companies concerned
07:57do not fully account for these huge multidirectional waves.
08:01There seems to be a lot of similarity between these two phenomena,
08:05but tsunamis are different.
08:07They occur during earthquakes, volcanic eruptions,
08:10or landslides.
08:12These phenomena disturb the entire water column.
08:15At sea, you may not even notice that a tsunami
08:19is occurring.
08:20But near the shore,
08:22when they come into contact with shallow waters,
08:25these waves can reach unthinkable heights.
08:28Accelerated waves form on the surface.
08:32However, they can sometimes form in the depths.
08:36And we are talking about internal accelerated waves.