Si vous pensez que le mont Vésuve est effrayant, attendez d'entendre parler de Campi Flegrei ! Ce supervolcan a 24 cratères souterrains et fait paraître le Vésuve petit en comparaison. La partie folle ? Un demi-million de personnes vivent directement dans la zone de danger aujourd'hui ! Bien qu'il n'ait pas éclaté depuis 500 ans, les scientifiques ont remarqué qu'il devenait plus actif ces derniers temps. Avec plus de 1 000 petites secousses chaque mois, les gens commencent à prêter attention. Si Campi Flegrei explose, cela pourrait être une catastrophe majeure ! Animation créée par Sympa.
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FunTranscript
00:00The last eruption of this volcano dates back to about 500 years, but recently it began to emit small earthquakes very frequently.
00:08Scientists record more than 1,000 per month.
00:12Of course, I want to talk about the super volcano known as the Flegraean field, located in Italy.
00:18A few weeks ago, the region was shaken by an earthquake of a magnitude of 4.4, with 150 earthquakes in one night.
00:27This is the most powerful earthquake in more than 40 years.
00:31Many inhabitants spent the night in their cars.
00:34And in the morning, these earthquakes were followed by a second earthquake, a little weaker, of a magnitude of 3.6.
00:42Is Italy in danger?
00:45The earthquake itself was not significant enough to cause serious damage, but it caused panic.
00:52At the moment, local authorities are developing ambitious emergency plans.
00:56If the worst happens, they will have to evacuate hundreds of thousands of people.
01:01One of the reasons is the proximity of this area to Naples, which has more than 3 million inhabitants.
01:07Governments even consider paying people to leave their homes.
01:14For the moment, schools remain closed in the Flegraean field region.
01:18Authorities are allocating more than 500 million euros to ensure the safety of buildings and constructions.
01:25A yellow alert is still in force in the area, where 80,000 people live.
01:31There is also the red zone, the most dangerous.
01:351,250 houses are located there, and all are exposed to a high seismic risk in the event of an eruption.
01:42In addition, more than twice as many houses will be exposed to an average risk.
01:49Italy is a country subject to seismic activity.
01:52Epuzole is a densely populated city, located on one of the most dangerous volcanoes in Europe.
01:59The Flegraean fields have 24 underground craters.
02:03Next to them, the famous Vesuvius is rather pale.
02:07Yes, the volcano that made the Roman city of Pompeii disappear from the surface of the earth in 79 AD.
02:15This city flourished near the base of Vesuvius, in the bay of Naples.
02:19At the time of the first Roman Empire, 20,000 people lived in Pompeii.
02:24They were merchants, industrialists, farmers, etc.
02:28The soil of the region was rich and fertile, which explains the presence of many shepherds and vineyards.
02:34Curiously, no one knew that this black earth was the result of a previous eruption of Vesuvius.
02:41The region was one of the favorite summer destinations of the fortunate Romans.
02:45Unfortunately, on August 24, 79, at noon, all this prosperity disappeared.
02:51The top of Vesuvius exploded, projecting in the stratosphere a cloud of ash and sandstone of a height of 16 km.
02:59During the 12 hours that followed, the eruption wreaked havoc in the city.
03:05Volcanic ashes and a stone ridge, some of which were more than 7 cm in diameter, fell on Pompeii.
03:12The inhabitants of the city had to flee, terrorized.
03:15About 2,000 people hid in stone structures and in caves, paralyzed by fear.
03:21They hoped to be able to wait for the end of the eruption.
03:24Who knows, if they had decided to leave the city at the very beginning of the eruption, they might have had a chance to survive.
03:32A west wind protected the city from the first effects of the eruption.
03:36But soon, a gigantic cloud of ashes and burning gas unveiled the west side of Vesuvius.
03:42It engulfed the city, burning everything in its path.
03:46This devastating cloud was followed by a flood of mud and volcanic rocks that completely engulfed the city.
03:52As if the volcano wanted to make sure that no one would survive.
03:56A toxic gas cloud then poured into the city, putting an end to the lives of the few survivors on August 25.
04:03A stream of rocks and ashes followed, crushing roofs and walls and turning the city into a gigantic cemetery.
04:15When a supervolcano erupts, the consequences are usually catastrophic.
04:20Supervolcanoes have experienced at least one eruption whose explosive index was 8, which is the highest ever recorded.
04:28Supervolcanoes are often extremely large and do not have many cones.
04:33This is explained by the fact that they are generally the remains of gigantic magmatic chambers that have once exploded, leaving behind a caldera.
04:42These chambers are generally located above hot spots and manifest when huge volumes of magma try to escape from the depths of the subsurface and end up bursting at the surface of the earth.
04:54Sometimes, all this magma remains blocked, unable to pierce the earth's crust.
04:59It is then that huge seas of magma under pressure gather at several kilometers deep.
05:05The pressure continues to increase as more and more magma tries to rise to the surface.
05:10At some point, a super-eruption occurs.
05:13The most recent known super-eruption took place in New Zealand.
05:17When I say recent, I mean that it occurred about 26,500 years ago.
05:23A supervolcano located on the surface of Lake Taupo projected more than 1,250 km3 of ashes and sandstone into the air.
05:32Imagine 500,000 large pyramids of geysers flying at the same time.
05:39It is to say the incredible power of this eruption.
05:42But the most fascinating and the most disconcerting in this eruption is that the Taupo volcano did not just go out like many others.
05:51At first, everything went as usual.
05:53Tons and tons of magma under pressure had accumulated under the surface and the pressure was getting stronger and stronger.
06:00But once the first cracks appeared and the first portion of lava came out of the crater, something went wrong and the supervolcano took a break.
06:09It was only a few months later that the disastrous eruption shook the ground.
06:14Thousands of tons of lava, rocks and ashes flew into the atmosphere.
06:19The unusual configuration of Lake Taupo still disconcerts scientists.
06:24The Indonesian eruption of the Toba caldera 75,000 years ago was the most important in the last two million years.
06:32Experts estimate that the eruption could have released hundreds of thousands of tons of sulfuric acid,
06:38which could even have caused a cooling of several degrees on the planet's surface.
06:43But today, the impact is difficult to detect due to the glaciers that covered the ground later.
06:49There are also several supervolcanoes that have not yet deserved this name because they have never produced super-eruptions.
06:56For example, in 1883, the Indonesian volcano Krakatoa exploded.
07:02The power of the eruption tore the walls of the volcano.
07:06The sea water then infiltrated its fusing entrails.
07:10The difference in temperature caused the volcano to explode in a deafening noise.
07:14We clearly heard it 4,800 km away, in Australia.
07:19It was worth the explosion the loudest noise in history.
07:24But even if the consequences of this event were really catastrophic,
07:28it turned out that it was not powerful enough to be considered a super-eruption.
07:33The volcanic explosiveness index was only 6.
07:39There is also the Mauna Loa.
07:41It is a shield volcano, which means that it does not produce explosive eruptions.
07:46But its size makes this monster an extremely dangerous volcano.
07:52For the moment, the volcano seems to be at peace with its environment.
07:55Research equipment shows no signs of activity.
07:59But if the Mauna Loa suddenly erupted,
08:02lava flows could reach the ocean and the most populated and touristic places,
08:06like Captain Cook's territorial area, very quickly, in a few hours only.
08:12The last time this volcano erupted, lava reached the outskirts of Hilo, on the other side of the island.
08:18This is where the University of Hawaii is located.
08:21Fortunately, the inhabitants had a few weeks in advance to prepare for the disaster.
08:26Throughout its history, the Mauna Loa has erupted quite regularly, almost every six years.
08:32On the other hand, the Big Island volcanoes are not very volatile.
08:36The reason is that they are shield volcanoes.
08:40These volcanoes have received this name because they are not very high,
08:43and that they look like a shield of warriors lying flat on the ground.
08:47Shield volcanoes are formed by a very fluid lava.
08:51They move much further and form much finer flows than the lava from a stratovolcano,
08:57which has a conical shape and is high, like the infamous Krakatoa in Indonesia.
09:02Therefore, if the Mauna Loa erupts one day,
09:06there will probably be no clouds of ash or tons of debris.
09:10It is the lava that will be the most dangerous.
09:12The Mauna Loa, being a shield volcano,
09:15its lava is extremely fluid and voluminous, which allows it to flow far and fast.