00:00Something enormous is just in Hawaii,
00:03deeper deep than any one can ever reach.
00:06This strange strange island,
00:08at about 2.900 km of depth,
00:11reveals the details of the formation of the islands
00:14and could cause an eruption that affects thousands of lives.
00:20The scientists call these strange formations
00:23zones at ultra-bass speed.
00:25When the waves are happening,
00:27they send vibrations across the planet,
00:30which quickly traverse the most of the rocks,
00:32but ralentisent considerably,
00:34passing by some deep couches.
00:36This ralentissement indique to the geologist
00:39that something unusual is there.
00:41The giant mass in Hawaii
00:43belongs to the biggest category of its structures,
00:46a mega-zone at ultra-bass speed,
00:49a huge amount of material
00:51located directly at the frontier
00:52between the Earth's manteau and its loyau.
00:55To discover what really looks like this monster,
00:58scientists have followed
00:59two different types of sismic types.
01:02The first type,
01:03the ones of pressure,
01:04comprise the rocks like a ressort that we're going through.
01:07The other type,
01:08the ones of cisaillement,
01:10make oscillate the rocks from haut and bas,
01:11like when we're going through a cord.
01:13In combining the two signals,
01:15the researchers have been able to dress
01:16a much more precise portrait
01:17of what is in the depths of Hawaii.
01:19The scientists thought
01:21that this mass was molle
01:23and partially fondue,
01:24like the lava épaisse
01:26coming towards the surface.
01:28But these new data sismic
01:29have shown that the mass
01:31is not at all viscous.
01:32It's especially
01:33a solid, dense,
01:36dense,
01:36lourd
01:36and gorgé de fer.
01:38This discovery
01:39helps explain
01:40a real mystery
01:40which has intrigued
01:41the scientists
01:42for decades.
01:43Most of the volcanoes
01:44are formed
01:45along the borders
01:46of the Arctic.
01:47But Hawaii
01:48is not located
01:49anywhere
01:49near its frontiers.
01:51The archipel
01:52flotting
01:53in the middle
01:53of the Pacific Pacific.
01:54And yet,
01:55the islands
01:56are formed
01:56from certain
01:57of the most active
01:59of the planet.
02:00We explained it
02:01by a hot
02:01point
02:02hot,
02:02a column of heat
02:03coming from the
02:04depths of the Earth,
02:05like a chalimau
02:07fondant lentement
02:08its way towards the top.
02:09But it seems
02:10that this giant mass
02:11giant
02:11rich in fer
02:13encre the
02:13panache
02:13of the heat
02:14in place,
02:15like the base
02:15of a lamp
02:16to lava
02:16which maintains
02:17the flow
02:18regularly
02:18for millions of years.
02:21The material
02:22which is composed
02:23could even
02:24be a vestige
02:25of an ocean
02:26magmatic
02:26basal,
02:27a gigantic
02:28cloud
02:29of the Earth
02:31during its formation.
02:33When this ancient
02:34ocean
02:35is cold
02:35and crystallized,
02:37the elements
02:37lourds
02:38like the fer
02:39have been
02:39created
02:39deep
02:40and the mass
02:43of Hawaii
02:44could be one
02:45of its survivors.
02:46Or,
02:47the structures
02:48like this
02:48do not remain
02:49in place
02:50forever.
02:52The heat
02:53constantly
02:53in the earth
02:55and when these
02:56flux change,
02:57they can
02:58tire
02:58on the surface
02:59and sometimes
03:02destabilize.
03:03If the system
03:04under Hawaii
03:05came to change
03:06significantly,
03:07it could
03:08intensify
03:09the volcanic activity
03:09in the surface.
03:11We already see
03:12signs of this
03:13agitement.
03:14Hawaii
03:14has thousands
03:15of eruptions
03:16every year.
03:17Most of them
03:18are minuscules,
03:19as weak as
03:20only the sensitive instruments
03:21detect them.
03:22In average,
03:23Hawaii
03:24has about
03:24100 eruptions
03:25of magnitude 3
03:26per year.
03:28Those are
03:29very strong
03:29to be felt
03:30by the population.
03:31Environ
03:3110
03:32séismes
03:32reach
03:33magnitude 4
03:34each year.
03:35And about
03:351
03:36of magnitude 5
03:37secoue
03:38every year.
03:39The most important
03:41events
03:41are more rare,
03:42but they
03:42are still
03:43happening.
03:44The essential
03:44of this activity
03:45is around
03:46the Grand Isle,
03:47which includes
03:48several volcanoes.
03:49At the beginning
03:50of March
03:502026,
03:52the Kilauea
03:52has projected
03:53the mountains
03:54of the lava
03:54at about 400
03:55meters
03:56in the air.
03:58The red
03:58red
03:58red
03:58rocks
03:59in fusion
04:00have fallen
04:00into the sky.
04:01The
04:06authorities have
04:07temporarily
04:08closed the parts
04:09of the national park
04:09and the sections
04:11of the highway
04:1211,
04:12because the
04:13retombées
04:13of the debris
04:14created dangerous conditions.
04:16The eruption
04:17has not directly
04:18impeded
04:18the buildings,
04:19but it has
04:19caused real problems.
04:21The cindes
04:22have spread
04:23on the communities
04:24and the minuscules fragments
04:26of the roads
04:26and the toits.
04:28This activity
04:30is linked
04:30to the same
04:31deep
04:31the point
04:33hot
04:33encased
04:34by this enormous
04:34mass rich
04:35in fer
04:36at 2.900
04:37kilometers
04:38under the
04:39sea.
04:40Now,
04:41we are going
04:41to the north
04:42where something
04:43quite
04:43scary
04:44is found
04:45beneath
04:45the west
04:45of the
04:46North.
04:46The scientists
04:51think
04:52that two
04:53big
04:53big
04:53seismic
04:54areas
04:54are not
04:56on the coast
05:00but could
05:01influence
05:02mutually
05:02and act
05:03like
05:03the
05:04Pacific
05:04the
05:06west
05:06Pacific
05:06goes
05:06along the
05:07nearby
05:07California.
05:12The scientists
05:13have found
05:13evidence
05:14of the
05:14sea.
05:16They have
05:17extravagant
05:18buried
05:19at the
05:20And these carottes are like books of geological history
05:23which concern the couches of debris of the ancient ships.
05:27In these couches, researchers have observed
05:29that the pairs of seismic ships are almost overposed.
05:34The geologists call them the double.
05:37Two massive ships are produced so close in the time
05:41that the ocean has just a time to stabilize between the two.
05:44And this discovery points directly
05:47towards the one of the tectonics the most chaotic planet,
05:50the triple jonction of Mendocino.
05:53It's there that the three tectonics enter in collision
05:56and grinds the unes against the other,
05:58like the engrenages in a machine.
06:00It's also the exact place where the faille of San Andreas
06:03meets the zone of subduction of Cascadia.
06:07Or, when a faille se rom,
06:09she sends waves of contraintes through the croûte.
06:13This contraintes can destabilize the faille voisine
06:15and the poussée towards the rupture at his turn.
06:18A mega-séisme of Cascadia,
06:20a lui-seul,
06:21could reach a magnitude 9 or more.
06:24This type of seismic
06:25could open 600 to 700 miles of fonds marins
06:28and send a massive tsunami to the Pacific.
06:33And if Cascadia se rom in the first,
06:35the transfer of contraintes
06:37could cause the faille of San Andreas a little later.
06:39In the worst case,
06:41the inhabitants of California
06:42could feel a huge disaster,
06:45see the buildings oscillate
06:47and the auto-routes be broken,
06:48then experience a second catastrophe
06:50a few minutes later.
06:52And the inverse sequence could also occur.
06:55The faille of San Andreas
06:57could see in the first,
06:58distribute the pressure in the croûte
07:00and push Cascadia to the rupture.
07:03In this case,
07:04the inhabitants of the touch zone
07:05could survive the first seismic,
07:07then see the ocean
07:09suddenly retire from the rivage.
07:11And it's the signal glaçant
07:12that a tsunami could arrive
07:14in about 20 minutes.
07:17The scientists know,
07:19thanks to the analysis of the sediment,
07:20that this sequence is already produced.
07:22There were at least 10 seismic
07:24in the last 3100 years.
07:28The most frightening,
07:29it's not a question of if,
07:33but strictly of when.
07:35Now,
07:36we're going to go to the Atlantic
07:37to the south of Italy.
07:39Just to the west of Naples,
07:40there is a mass mass system
07:42called the Caldera
07:43of Campi Flegrei.
07:45It means something like
07:47the
07:47and this name was well worth it.
07:50It's about 109000 years ago,
07:53an enormous eruption
07:54has projected
07:54the sand and the roches
07:55across the whole region.
07:57It has evacuated
07:58more than 150 km3
08:00of magma
08:01under the surface.
08:03It's a volume
08:04close to the massive eruption
08:05that formed the Caldera
08:07of Campi Flegrei
08:08it's about 40.000 years ago.
08:10This eruption
08:11anterior
08:11has creased
08:12a craté
08:12of about 15 km
08:13large and dispersed
08:15from volcanic cendres
08:16over many parts of Europe.
08:19Today,
08:20more than 400000 people
08:21live directly
08:22inside this ancient crater.
08:23The soil
08:25is incredibly fertile
08:26because the cultures
08:28poussent
08:28on the volcanic cendres
08:29decomposed
08:30for centuries.
08:31But the same geology
08:33which makes these
08:34fertile
08:34also
08:35a colossal energy
08:37under the surface.
08:39The researchers
08:39have recently studied
08:41the ancient
08:41couches rocheuses
08:42preserved in the mountains
08:43and the forages
08:44profonds
08:45of the region.
08:46It's so that
08:46they discovered
08:47that the Campi
08:48Flegrei
08:49produce perhaps
08:50some of the eruptions
08:53that doesn't mean
08:55that an eruption
08:55catastrophic
08:56is imminent.
08:57But it changes
08:58the way
08:59the researchers
08:59perceive the danger
09:01to long term.
09:03When these eruptions
09:04are happening,
09:05they don't behave
09:06like an eruption
09:06of the ordinary.
09:08They generate
09:09an eruption
09:09of pyroclastics,
09:10an avalanches
09:11of gas
09:12burning,
09:12of cendres
09:13and of roches
09:14which devalent
09:15the soil
09:15at the speed
09:16of an autoroute.
09:18Some of the ancient
09:20eruptions
09:20of this eruption
09:21datant
09:21of more than 100.000
09:23atteignent
09:23près de 2 mètres
09:24d'épaisseur
09:25par endroit,
09:25ce qui prouve
09:26à quel point
09:27l'explosion
09:27fit violente.
09:31Quand on relie
09:32toutes ces découvertes,
09:33on voit une fois
09:34de plus
09:35que notre planète
09:36ne reste pas
09:36tranquillement
09:37immobile
09:38sous nos pieds.
09:39Elle bouge,
09:40elle respire
09:40et parfois
09:41elle nous rappelle
09:42qui commande
09:43vraiment ici.
09:45Et la plupart
09:45du temps,
09:46les plus grandes forces
09:47qui façonnent
09:48notre monde
09:48se cachent
09:49à des milliers
09:50de kilomètres
09:51sous nos pieds.
09:52Sous-titrage Société Radio-Canada
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