Cette Catastrophe Océanique Pourrait Paralyser le Monde Entier

Sympa

Les avalanches sous-marines, ou "glissements de terrain sous-marins", peuvent sembler sortir tout droit d'un film de science-fiction, mais elles représentent un réel danger ! 🌊 Ces événements se produisent lorsque de grandes quantités de sédiments ou de débris glissent soudainement le long du fond océanique, provoquant d'énormes perturbations. La force de ces avalanches peut déclencher des tsunamis gigantesques, traversant l'océan et frappant les zones côtières avec peu d'avertissement. 🌊 Ce qui est effrayant, c'est qu'il est difficile de les prévoir, surtout parce qu'elles surviennent souvent dans des parties profondes et reculées de l'océan. Les scientifiques les étudient davantage pour comprendre les risques, mais le danger est bien réel. C'est un rappel que l'océan peut être aussi imprévisible et puissant que n'importe quoi sur terre !  Animation créée par Sympa. ---------------------------------------------------------------------------------------- Musique par Epidemic Sound https://www.epidemicsound.com   Pour ne rien perdre de Sympa, abonnez-vous!: https://goo.gl/6E4Xna​ ---------------------------------------------------------------------------------------- Nos réseaux sociaux : Facebook: https://www.facebook.com/sympasympacom/ Instagram: https://www.instagram.com/sympa.officiel/  Stock de fichiers (photos, vidéos et autres): https://www.depositphotos.com https://www.shutterstock.com https://www.eastnews.ru ----------------------------------------------------------------------------------------  Si tu en veux encore plus, fais un tour ici:  http://sympa-sympa.com

Transcript

00:00The snowy coat above you suddenly folds in two,

00:05unveiling the icy slope to its resting point well below.

00:10On its way, everything is crumbled under the enormous mass of snow and debris.

00:15You are witnessing an avalanche, one of the most dreadful natural disasters ever.

00:21And if you were told about another type of avalanche, just as terrifying as that of the mountains,

00:26what makes it particularly strange is that it occurs underwater.

00:31Underwater avalanches are natural phenomena of devastating power,

00:36often far more formidable than terrestrial ones.

00:39They can cause planetary chaos with dramatic consequences.

00:44The most disturbing is that they constantly occur under the surface of the oceans,

00:49invisible, unpredictable and extremely difficult to measure.

00:54These underwater avalanches can reach a magnitude 100 times greater than those of terrestrial avalanches

01:00and gravely threaten global communications,

01:03to the point of potentially depriving the entire planet of internet.

01:07But we will come back to this later.

01:09For now, let's go back 60,000 years in the past.

01:13Here we are off the northwest coast of Africa,

01:16about to discover the magnitude and devastating impact of a titanic underwater avalanche.

01:23It began with a simple slip of underwater terrain in the Agadir Canyon.

01:28Originally, it was only one and a half cubic kilometers of material.

01:33However, this mass was quickly multiplied by more than 100 by crossing the bottom of the Atlantic Ocean.

01:41As the avalanche gained speed and volume,

01:44it carried with it gravel, sand, rocks and mud.

01:48It dug a devastating trench through one of the largest underwater canyons in the world,

01:53eradicating any form of life on its way.

01:56The power of the destructive flow was such that it eroded a segment of 400 kilometers of the canyon,

02:01digging hundreds of meters into its walls and damaging a total area of 4,500 square kilometers,

02:07more than three and a half times the surface of New York.

02:10As for its strength, it projected huge rock blocks along the walls of the canyon,

02:15reaching heights of up to 130 meters.

02:19Before the scientists highlighted this devastating event,

02:23they had largely underestimated the extent of the destruction caused by underwater avalanches.

02:29In addition, these major disasters can occur not only offshore, in the ocean depths,

02:35but also near the estuaries.

02:38Let's go back to January 14, 2020 to examine this more closely.

02:42A current of turbidity, a rapid flow of water descending loaded with sediment,

02:46traveled more than 1,100 kilometers from the estuary of the Congo River to the abysses.

02:51This phenomenon was caused by two factors.

02:53Exceptional floods along the river at the end of December 2019

02:58and spring tides of an unusual magnitude.

03:01This generated a gigantic avalanche of sand and mud,

03:05of which the volume represented a third of all the sediments transported annually by all the rivers on the planet.

03:11This avalanche saw its speed increase,

03:14going from 5 meters per second in the upper part of the Congo Canyon

03:18to 8 meters per second at the end of the canal,

03:21after 1,200 kilometers from the coast.

03:24This journey made it the longest avalanche of sediment ever measured on Earth.

03:28Two days after its launch, the flow reached the abysses.

03:32The avalanche cut two underwater telecommunications cables,

03:36drastically slowing the transfer of Internet data

03:39across West, Central and South Africa.

03:43Before that, scientists considered it impossible to directly measure large-scale underwater avalanches.

03:50However, the flow of sediment observed in the Congo Canyon

03:54allowed to monitor the phenomenon,

03:56offering researchers a better understanding of the link

03:59between large riverbanks and ocean depths.

04:03They also determined that the frequency of underwater avalanches

04:07depended on the location of the observer.

04:10Submarine canyons, located near the mouth of rivers,

04:13can detect several small avalanches each year.

04:16However, systems far from riverbeds, such as the Agadir Canyon,

04:21only experience a titanic avalanche every 10,000 years or so.

04:26You may be wondering about the possible causes of an underwater avalanche.

04:31Earthquakes, typhoons, high tides, river floods

04:35and even volcanic eruptions can be responsible.

04:39In addition, with climate change, these phenomena become more and more frequent and violent.

04:45However, the presence of these triggers does not guarantee that an avalanche will occur

04:50or determine its magnitude.

04:52Let's take an example.

04:53In 1755, a powerful earthquake hit the Portuguese coast,

04:58devastating Lisbon and causing tens of thousands of deaths.

05:02However, this event only caused a small underwater avalanche.

05:07However, in 1929, a major earthquake off Newfoundland, Canada,

05:12triggered the largest underwater avalanche ever documented.

05:17The flow, traveling at 70 km per hour,

05:20carried rocks, sand and mud while breaking 11 underwater cables.

05:26The power of the avalanche also generated a tsunami,

05:29causing the death of 28 people along the coast.

05:33Underwater avalanches are invisible because they occur in depth,

05:37which makes their study extremely complex.

05:40However, their understanding is crucial.

05:42These flows transport sediments, nutrients and even pollutants through the seabed,

05:48playing an essential role in oceanic ecosystems.

05:52A team of researchers from Liverpool then started to solve this mystery.

05:57Over the past four decades,

05:59they have collected more than 300 samples from the ocean floor,

06:03associating them to seismic and bathymetric data.

06:06In other words, to the cartography of the seabed.

06:09They were able to reconstruct a huge underwater avalanche,

06:12a first at this scale.

06:15What makes the event even more fascinating

06:17is that it started relatively modestly

06:19before transforming into a gigantic avalanche,

06:22reaching more than 200 meters in height.

06:25To imagine the magnitude,

06:26think of an avalanche the size of a skyscraper in Liverpool, London,

06:30digging a trench 30 meters deep and 15 kilometers wide.

06:35Finally, it spread over a surface higher than that of the United Kingdom,

06:40covering everything with a thick layer of sand and mud.

06:43It's like burying an entire country.

06:46These discoveries are truly crucial,

06:49because they reveal that a low-magnitude undersea landslide

06:53can evolve into a gigantic and highly destructive phenomenon.

06:57But the most worrying are the underwater internet cables,

07:01essential to global communication.

07:04There are more than 550 active cables on the seabed,

07:07totaling an incredible length of 1,400,000 kilometers,

07:11which is enough to surround the Earth 35 times.

07:15When such an avalanche damages underwater cables,

07:18the consequences are often catastrophic and costly.

07:22In 2006, a typhoon in Taiwan caused underwater avalanches

07:26that cut several cables linking Southeast Asia to the rest of the world.

07:31This led to a loss of 90% of internet traffic

07:35between China and the United States at the peak of the event.

07:38Taiwan, on the other hand,

07:40experienced traffic interruptions going from 74% to 100% to neighboring islands.

07:45You now understand why it is essential to know more about this natural phenomenon.

07:50Fortunately, researchers at the University of Tulane

07:54have found a way to analyze it in three dimensions.

07:57So far, studies have only considered undersea avalanches in two dimensions,

08:02which did not fully capture their behavior.

08:07Researchers have focused their efforts on the interaction of undersea flows

08:11with mini-pools, natural formations on the ocean floor

08:15resembling shallow bowls.

08:17Despite their name, these pools can be vast,

08:20reaching up to 10 square kilometers,

08:23which is about twice the area of Central Park in New York.

08:27When currents of turbidity enter these mini-pools,

08:31they do not simply move.

08:33On the contrary, they hit the opposite wall

08:36and return in the form of whirlpools,

08:38similar to tides in a watercourse.

08:41These whirling movements redistribute the sediments

08:45before they settle.

08:47The size of the pool and the speed of the current

08:50strongly influence this process.

08:53If the pool is large and the current is slow,

08:56it gradually fills up with sediments.

08:58But if the current accelerates or if the pool is reduced,

09:01the flow overflows,

09:03spreading beyond its limits.

09:06To further their research,

09:08scientists have created a replica of a mini-pool in a swimming pool

09:12and tested various flow speeds

09:15to simulate currents of turbidity.

09:17They even designed specific sediment mixtures

09:20to observe the behavior of particles of various sizes.

09:24Finally, they succeeded in reproducing oceanic conditions,

09:28but on a controllable scale and adapted to their experiments.

09:32Fascinating, isn't it?

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