00:00Ah, the sea is agitated today. Nothing alarming, but enough to cause some discomfort.
00:08A diffuse anxiety invades you, a kind of foreboding. Something serious seems to be about to happen.
00:14And suddenly, panicked screams resound.
00:17When you turn around, you see a huge wave, much higher than all the others.
00:22Could it be a tsunami?
00:24That's right. When we speak of devastating waves, it is usually tsunamis that immediately come to mind.
00:31However, the one that is about to hit your ship is not one.
00:35It is a stormy wave.
00:37Although tsunamis and stormy waves can both cause disasters,
00:41they differ so much by their origin that by the places where their devastation is exercised.
00:46Imagine now a colossal wave, reaching 18 meters in height, projected on your ship.
00:52It is a miracle that the ship does not sink.
00:55This massive wave, a celerate wave, seems to have materialized suddenly, as if it came from nowhere.
01:02As disturbing, unpredictable and isolated as they may seem,
01:06celerate waves are not as rare as one might think.
01:10To better visualize, take the average height of a room in your house.
01:14The ceiling is probably a little less than 3 meters.
01:16A two-story house usually measures between 6 and 9 meters.
01:20As for the Statue of Liberty, it reaches 34 meters if you measure from the feet to the head.
01:25With these benchmarks, you can get an idea of the dimensions of the celerate waves,
01:30whose highest measurements are 15 to 30 meters.
01:33For a wave to be classified as celerate, it must arise unexpectedly and exceed the surrounding waves in height.
01:40But the exact measurement of this gap remains unresolved.
01:43Some specialists believe that a celerate wave must be at least twice as high as the other major waves nearby,
01:50while others do not share this opinion.
01:53Celerate waves are also distinguished by their steeper slopes compared to classic waves,
01:58which generally adopt the shape of a large swell.
02:02This configuration allows ships to sink such waves, even when they are very high.
02:07A celerate wave, on the other hand, looks like a real water wall.
02:12Because of its steeper slope, it hits the ships with colossal force,
02:17sometimes being able to roll over the building.
02:20Celerate waves remain partly mysterious,
02:23especially because no one has ever filmed their formation or followed their entire life cycle.
02:28We have some photographs of these exceptional waves.
02:31However, for centuries, their existence was based only on legends and stories of sailors who survived such encounters.
02:39Scientists have not yet elucidated the exact mechanism at the origin of celerate waves.
02:44A theory evokes a phenomenon of wave reinforcement.
02:48This occurs when two waves interact and their heights combine.
02:53For example, if a 5-meter wave crosses another 10 meters, let's do the math,
02:58it can give birth to an ephemeral wave reaching 15 meters.
03:02Celerate waves are not limited to the oceans.
03:06On November 10, 1975, on Lake Superior,
03:09a group of three celerate waves, nicknamed the Three Sisters,
03:13could have caused the shipwreck of the SS Edmund Fitzgerald, an American cargo ship sailing on the Great Lakes.
03:19This disaster led to the loss of the ship and all its crew members.
03:24These waves followed each other at an interval too close,
03:27preventing the ship from stabilizing and cutting the water brought by the first before the next hit.
03:33The captain of a ship close to the Fitzgerald reported that his building had been hit by two waves from 9 to 10 meters high.
03:40These waves, presumably followed by a third,
03:43would then have pursued their course towards the Fitzgerald, contributing to its shipwreck.
03:48Let's leave this subject aside and go back to the tsunami.
03:51These natural disasters represent an extreme danger and radically differ from celerate waves.
03:57In most cases, a tsunami is caused by an underwater earthquake.
04:01When it is formed, it usually measures only a few meters in height.
04:05However, as it approaches the coast, it increases in size.
04:09By entering shallow waters, it begins to slow down.
04:13The first wave then hits the coast, its summit moving faster than its base,
04:18which explains its height and its dizzying slope.
04:21The lowest point of the wave hits the earth first,
04:24generating a vacuum effect that sucks water away from the shore, exposing the bay and the seabed.
04:30People able to identify this first sign of a tsunami can still have a chance to save their skin.
04:36A few minutes later, a gigantic water wall falls on the coast, destroying everything in its path.
04:42But it is not a single wave.
04:44A train of waves is formed, composed of multiple successive waves.
04:49The speed of this train does not depend on the distance to the epicenter, but on the depth of the ocean.
04:55At sea, tsunamis can reach the speed of a jet plane.
04:59However, when they enter shallow waters, their progression slows down considerably.
05:05The first wave of a tsunami is usually not the most powerful.
05:09However, many people are unaware of this fact and make the mistake of releasing their vigilance after it passes.
05:15They believe in the remote danger, which exposes them to the following waves,
05:19often much more imposing and destructive, which take them by surprise.
05:23A tsunami can sometimes manifest itself in the form of a torrent of boiling water.
05:27At other times, it causes a sudden retreat of the sea, leaving behind failed fish and overturned boats.
05:34In addition, a slight rise in the sea level can also indicate the imminent arrival of a tsunami.
05:40If the first wave reaches the shore, the second, often larger, can occur after a certain delay.
05:47You can also observe the boiling, turbulent sea water and form strange patterns.
05:53It is another indisputable clue that a tsunami is imminent.
05:56Repeated successive waves can also indicate the approach of a tsunami.
06:01If you notice unusual swells following each other at regular intervals,
06:05it would be wise to quickly head to an elevated area.
06:09Surprisingly, some of the most gigantic tsunamis have been caused by landslides.
06:16A striking example is that of the Lituya Bay, in Alaska,
06:20where a landslide generated a wave of 520 meters high, one of the most impressive ever recorded.
06:26This colossal wave swept across the peninsula, carrying trees, vegetation and sweeping the ground to the bare rock.
06:34Its height was equivalent to more than half that of the Burj Khalifa, the highest structure in the world.
06:40Likewise, when a third of the Hawaiian volcano, East Molokai, collapsed in the Pacific Ocean,
06:46it triggered a tsunami reaching 610 meters, or the height of the Shanghai Tower, one of the highest skyscrapers in the world.
06:54Another strange and potentially dangerous oceanic phenomenon is that of the crossed sea.
06:59It is formed when two distinct wave systems meet at right angles,
07:04which often occurs near peninsulas, or where two seas or oceans meet.
07:09This spectacle may seem impressive, but only from the shore.
07:13It is strongly not advisable to throw yourself into the water to interact with these waves.
07:17The countercurrents that are there can easily drag the most experienced swimmers under the surface.
07:23Square waves have also been responsible for many maritime disasters over time.
07:28In addition, if you see agitated waves, mixed with marine debris and algae, abstain from swimming.
07:34These signs can reveal the presence of a powerful torrent, capable of dragging you ashore.
07:40We now come to a much larger phenomenon, and even on a truly planetary scale.
07:44The Rossby waves. There are two types, oceanic and atmospheric.
07:49But given the theme of the day, let's focus on those related to the oceans.
07:54The Rossby waves, which move slowly, are completely different from surface waves.
07:59They are nothing like the waves that wave on the beaches.
08:03These are gigantic ocean movements, which extend horizontally over hundreds of kilometers across the planet, always to the west.
08:10Their magnitude is such that they can influence global climatic conditions, cause high tides, and even cause floods in certain regions.
08:19Their complex movement depends on their location.
08:22In the Pacific, the waves located near the equator take a few months to a year to cross the ocean.
08:28While those located further away from the equator may take more than 10 years to complete this same journey.
08:34So, when a wave passes, don't forget to give it a little sign.
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