00:00You recognize this mountain?
00:01Yes, it's the Everest.
00:03It's the most high mountain of the world, right?
00:06Well, apparently, no.
00:08There are two mountains,
00:10about 100 times higher than this giant.
00:12But you don't find it so easily.
00:17But let's start with a little comparison.
00:20The Everest,
00:21located at the border between the Népal and China,
00:24culminates at 8 848 m.
00:26It's about the altitude
00:28to which the plane flew.
00:29And even more surprising,
00:31it would seem that the Everest would continue to grow.
00:33It's about 40 cm
00:36every 100 years.
00:37The mountain has between 50 and 60 millions of years
00:40and formed by the collision
00:42of Indian and Eurasian plates.
00:47All this seems very impressive, right?
00:49I guarantee you change your opinion
00:50when I tell you what follows.
00:54Two monstrous structures
00:55are at the border between the noyau
00:57and the mantle of our planet.
01:00The one is located
01:01under Africa,
01:02and the other,
01:03under the Pacific Ocean.
01:05They seem to be the most big mountain
01:06of the planet.
01:07But they are not the classic mountains.
01:10Not the kind that we imagine
01:11when we hear the word mountain.
01:15These are incredible mountains
01:17culminate at about 1000 km from above.
01:20For comparison,
01:21the space begins officially
01:23at the line of Karman,
01:24at a altitude of 100 km
01:26above the surface terrestrial.
01:29So, if these mountains
01:30were at the surface of our planet,
01:32they would reach the space.
01:34Instead of that,
01:36they are completely hidden
01:37under the surface.
01:38The scientists think
01:40that these mountains
01:41have at least 500 millions
01:42of years
01:43and that they could even
01:44move on to the formation
01:45of the Earth
01:46there,
01:46there 4 billion years.
01:48Now,
01:49look at it.
01:51We can see that these monsters
01:53are at the border
01:54between the earth
01:54and the mantle.
01:56This thick,
01:57thick and semi-solid
01:58is just under the ground.
02:00There is an enormous amount
02:02of magnetic material
02:03tectonics.
02:04These are the pieces
02:05of the earth
02:05that have been pushed
02:06to the bottom
02:07from the surface.
02:09This is produced
02:10by a process called
02:11the subduction
02:12when a tectonic
02:14falls under the other
02:15and falls
02:15at the incredible depths
02:16of the depths.
02:19The scientists
02:20discovered these mountains
02:21were hidden
02:22by studying
02:22the seismic waves.
02:24During the big waves,
02:25our planet vibrate
02:26and sends
02:27to the surface.
02:29If the mountains
02:30ralentisent
02:31or change
02:31of direction,
02:32it indicates
02:33to the scientists
02:33that there is something
02:34that is habituel
02:35in the profondeur.
02:37These mountains
02:38ralentisent
02:39the mountains.
02:40That's why
02:40the researchers
02:41call them Large,
02:42Low, Sheer, Velocity, Provencies.
02:46The scientists
02:47still try to understand
02:48these massive formations.
02:50They don't know
02:51if these mountains
02:51are temporary
02:52and will end up
02:54to dissolve
02:54or if they are there
02:56in depth
02:56for hundreds
02:57to millions
02:57to millions
02:58to billions
02:59of years.
03:00These are
03:01one of the biggest structures
03:03and most mysterious
03:04of our planet.
03:06But there is
03:07an element
03:07that could help us
03:08to determine
03:09the real age
03:10of these mountains.
03:11These giants
03:12are more
03:13cold
03:14than the tectonic
03:15and normal
03:16the zones
03:17chaudes
03:18ralentisent
03:19the waves
03:20and absorb
03:22a lot of energy
03:22which is
03:23a lot
03:24of
03:25But
03:25with these
03:26structures
03:26géantes,
03:27something
03:27cloche.
03:28The
03:28ones
03:29are
03:29strong
03:29and intense.
03:31In the
03:32same
03:32time,
03:33tectonic
03:33froids
03:34absorb
03:34a lot
03:36of
03:36energy
03:36in the place.
03:38The
03:38searchers
03:39compare it
03:39to
03:45and
03:45the
03:45small
04:02the
04:02and
04:03the
04:04sea
04:04the
04:07and
04:07the
04:07sea
04:08is
04:09rich
04:09and
04:09the
04:10sea
04:10scientists have concluded that these huge mountains LLSVP are much more ancient than the
04:16cemeteries of the tectonic subduities that surround them.
04:20Probably they are very ancient, niches at the border between the noyau and the manteau
04:25for hundreds of millions, even billions of years.
04:30What makes these mountains even more concerning, is that their existence does not correspond
04:34to what we know of our planet or what we believed to know.
04:39Look, our planet is made of couches.
04:42At the outside is the croûte.
04:44Then comes the manteau, and at the center, the noyau.
04:47They have two parts, the internal and external.
04:52The problem is that we can't see the interior of the Earth,
04:55nor forest deep enough to extract the manteau.
04:59So scientists determine what is happening in using the seismic ones as we mentioned earlier.
05:04In studying the speed of the ones, their deviations or their ralentissements,
05:09scientists can draw an image of the inside of the Earth.
05:14It's a bit like using an echography to see the inside of the human body without opening it.
05:20The Earth's surface surface is formed.
05:22The surface surface is formed.
05:24The surface surface is formed.
05:25It's a big part of the manteau and the croûte.
05:27It's formed of about 15 tectonics.
05:30What does it look like?
05:32Just now, everything goes well.
05:33Let's continue.
05:33Few sustainable areas for place superficially,
05:37and from millions of years, theyue.
05:39L'Asténosphère.
05:40La roche chaude de l'Asténosphère
05:43se déplace lentement en courant,
05:45poussant les plaques.
05:46Les plaques tectoniques bougent à des vitesses différentes,
05:50généralement entre 2 et 15 cm par an.
05:53Ça semble très lent, non ?
05:55Et pourtant, sur des millions d'années,
05:57ça peut créer des formations extraordinaires.
06:00Par exemple,
06:01l'Himalaya, en Asie,
06:03est apparue quand deux plaques sont entrées en collision.
06:06Le rift est-africain
06:07s'est formé là où les plaques s'écartaient.
06:10Et la faille de San Andreas,
06:12en Californie, est l'endroit
06:13où les plaques glissent l'une contre l'autre.
06:17Mais les scientifiques ont remarqué quelque chose de curieux.
06:20La plupart des volcans apparaissent
06:22au-dessus des zones de subduction.
06:24Et c'est logique.
06:25Mais certains volcans se forment loin
06:27de toute frontière de plaques.
06:29Pourquoi ?
06:30En 1963, un géologue canadien
06:34a proposé une réponse.
06:35Il a dit que ces volcans
06:37apparaissaient au-dessus de points chauds dans le manteau.
06:40Un point chaud est une zone relativement fixe et très chaude,
06:43enfouie profondément dans la terre.
06:46Le magma du point chaud
06:47remonte à travers la plaque en mouvement au-dessus.
06:50Résultat ?
06:51Un volcan apparaît.
06:53Et à mesure que la plaque se déplace lentement
06:55au-dessus du point chaud,
06:56une chaîne d'îles volcaniques peut se former,
06:58comme les îles d'Hawaï.
07:00Mais revenons aux plaques tectoniques.
07:02Quand elles flottent sur le manteau
07:04et frottent les unes contre les autres à leur bord,
07:07cela déclenche des séismes.
07:09Vous vous souvenez sûrement
07:10que parfois, une plaque glisse sous une autre.
07:13Et au fil de millions d'années,
07:14des plaques entières peuvent s'enfoncer
07:16profondément dans le manteau.
07:19Les scientifiques avaient déjà étudié
07:21ces plaques englouties.
07:22Et à chaque fois, elles se trouvaient aux endroits
07:24où la subduction a lieu.
07:25Ce qui est logique.
07:29Cette fois, les chercheurs ont utilisé
07:31une nouvelle technique d'imagerie 3D
07:33appelée Full Waveform Inversion
07:35et ont découvert une structure géante
07:37sous le Pacifique.
07:39Mais il y avait un problème.
07:40Il n'y avait aucune zone de subduction
07:42au milieu du Pacifique.
07:44Donc, cette anomalie ne colle pas
07:46avec l'image habituelle du fonctionnement
07:48de notre planète.
07:50C'est comme si un médecin trouvait
07:52une artère au mauvais endroit dans un corps.
07:54Ça ne devrait pas exister.
07:56Et pourtant, c'est bien là.
07:57Alors, de quoi est faite cette anomalie ?
08:00Les scientifiques ont quelques idées,
08:02mais rien n'est certain pour l'instant.
08:04Il pourrait s'agir de roches anciennes
08:06riches en silice, présentes depuis
08:08la formation du manteau il y a environ
08:094 milliards d'années.
08:11Une autre hypothèse ?
08:12Ce serait des roches riches en fer
08:14qui se seraient lentement accumulées
08:16sur des milliards d'années avec les mouvements du manteau.
08:19Quoi qu'il en soit, cela nous montre
08:21que l'intérieur de la Terre est bien plus complexe
08:23qu'on ne le pensait.
08:25Dans tous les cas, la technique
08:27Full Waveform Inversion est extrêmement utile,
08:29car elle offre aux scientifiques
08:31une vision tridimensionnelle
08:32bien plus nette du manteau.
08:35Ces découvertes pourraient complètement
08:37changer notre compréhension
08:38des couches internes de la Terre.
08:40Étudier le manteau terrestre est vraiment
08:42essentiel si l'on veut comprendre
08:44comment notre planète a évolué
08:46au fil du temps.
08:48Ça aide aussi à expliquer ce qui se passe en surface,
08:51comme les volcans et la formation
08:53des montagnes.
08:55Le manteau agit comme le moteur
08:57de notre planète, alimentant
08:58tous ces phénomènes.
09:00Un exemple, ce qu'on appelle un panache menthélique.
09:03C'est comme une lampe à lave !
09:05De grosses masses de matière
09:07brûlantes remontent lentement
09:09des profondeurs de la Terre.
09:10Et quand elles atteignent enfin la surface,
09:13elles peuvent provoquer des irruptions volcaniques
09:15et remodeler le paysage.
09:17Il est essentiel de comprendre ces phénomènes
09:20pour se préparer aux catastrophes imminentes.
09:22C'est parti !
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