Si vous remarquez que les arbres sont plus verts près d'un volcan, il est judicieux de quitter les lieux. Cette verdure supplémentaire est due à l'intensification de l'activité volcanique, qui libère plus de dioxyde de carbone, élément que les plantes adorent. Cependant, une fois que le volcan entre vraiment en éruption, ces plantes deviennent brunes à cause du dioxyde de soufre nocif et de la chaleur intense. Ainsi, des arbres plus verts peuvent être un signe précurseur indiquant que le volcan pourrait bientôt se réveiller. En gros, si le feuillage commence à éclater, il est peut-être temps de décamper ! Animation créée par Sympa.
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FunTranscript
00:00 Could plants with a brighter green color warn us when a volcano erupts?
00:04 Indeed, contrary to earthquakes, which are extremely unpredictable,
00:09 volcanoes can sometimes show some signs of a forerunner.
00:12 The plants growing around volcanoes seem more active when volcanic activity increases,
00:18 because they benefit from high levels of carbon dioxide,
00:22 a gas emitted by volcanoes during eruptions and through underground magma.
00:27 They also acquire a brown hue when volcanic activity reaches its peak,
00:33 probably due to harmful gases and heat that damage the vegetation.
00:37 Scientists have discovered all this thanks to our satellites,
00:41 which they analyzed the data covering the period from 1984 to 2022.
00:46 Future changes could also be followed thanks to this imagery.
00:50 It is difficult to measure this phenomenon directly,
00:54 especially when volcanoes are located in inaccessible and luxurious areas,
00:58 such as the Tahal Volcano in the Philippines and Etna in Italy.
01:02 Thus, plants could warn us for years before an eruption occurs.
01:07 Thanks to this new method, we could protect neighboring communities
01:11 by reinforcing security measures, minimizing material damage,
01:15 and improving evacuation plans.
01:17 Volcanoes and plants are often mysteriously connected.
01:21 For example, the volcanic eruptions of Krakatoa in Indonesia
01:25 had a surprising effect on the saguaro cactus of the Sonora Desert in Arizona,
01:29 although they were thousands of kilometers away.
01:33 When the famous Krakatoa volcano erupted in the 19th century,
01:38 these shock waves swept the world,
01:40 and suddenly contributed to feed an entire generation of saguaros.
01:45 These impressive cactus can reach up to 12 meters in height at an adult age.
01:50 But they begin their lives as young plants struggling to survive in the harsh desert conditions.
01:56 However, thanks to the fresher and more humid conditions
02:00 caused by volcanic eruptions such as those of Krakatoa,
02:03 they can experience extraordinary growth growths.
02:06 The cooler summers and milder winters following such eruptions
02:10 create ideal conditions for young saguaros,
02:13 which generally do not survive due to extreme heat and intense cold.
02:17 But volcanoes do not only influence plants.
02:20 They are also the jewels of the Earth.
02:22 Deep under the surface, in the heart of a volcano,
02:26 the conditions are ideal for forming dazzling gems.
02:29 And during volcanic eruptions, these treasures can be brought back to the surface.
02:34 One of the most famous jewels created by volcanic activity is the diamond.
02:39 This is generally found in a rare type of volcanic rock called kimberlite,
02:44 which forms deeply inside our planet
02:47 under extreme pressures and temperatures.
02:51 Millions of years ago, eruptions of kimberlite,
02:54 small but powerful volcanic events,
02:57 extracted diamonds from the depths of the Earth.
03:00 This created the source of many current diamond mines.
03:04 These eruptions did not occur anywhere,
03:07 but came from continental cores, also known as cratons,
03:11 and arose as deeply as 120 km underground.
03:15 Feeding on a mixture of carbon dioxide and water,
03:18 they were like natural rockets,
03:21 exploding through the crust of the Earth to form carotid-shaped chimneys,
03:26 filled with minerals rich in diamonds.
03:28 Recently, scientists have explored the reasons for these eruptions.
03:32 They suggested that the rupture of ancient supercontinents, like the Pangaea,
03:36 disrupted the flow of the Earth's mantle below,
03:39 triggering these spectacular kimberlite eruptions.
03:42 When a volcano containing kimberlite erupts,
03:45 it can project its precious stones to the surface,
03:48 where they will finally be discovered.
03:50 There are other gems found in solidified lava,
03:53 like peridot, a brilliant green stone
03:56 that forms in the rock in fusion with the upper mantle
03:59 and is brought to the surface by volcanic activity.
04:02 There is also obsidian, a shiny rock, similar to glass,
04:06 which forms when lava cools rapidly.
04:08 And some incredible rocks can even hold water in their breasts,
04:12 even in lava.
04:13 The deeper we explore the volcanoes,
04:16 the more rare gems we discover.
04:18 By diving into the thick layer that is the mantle,
04:20 we can find olivine, a green mineral as resistant as trivalent,
04:25 which constitutes about half of this layer.
04:28 It appreciates high temperatures and easily forms in lava,
04:32 finally crystallizing into zinc rocks
04:35 that can be found on the Earth's surface thanks to eruptions.
04:38 As the olivine cools, it begins to crystallize.
04:41 Sometimes these crystals are tiny,
04:43 but other times they become larger
04:45 and can be polished into magnificent precious stones,
04:48 used in jewelry or in industrial processes such as metal melting.
04:53 However, by going deeper,
04:55 about 400 km underground,
04:58 olivine undergoes a fascinating transformation.
05:01 Here we meet the layer known as the transition zone.
05:05 In this region, the pressure is intense,
05:07 and the heat never stops growing.
05:09 This is where olivine metamorphoses into exotic minerals
05:12 such as wadsleyite and ringwoodite,
05:15 which have a beautiful green tint and a bright glow.
05:18 Although they are too rare and too small to be used in jewelry,
05:22 these minerals have the unique ability to hold water,
05:26 not in the form of droplets,
05:27 but as a compound of hydrogen and oxygen,
05:30 representing up to 3% of their volume.
05:33 It turned out that the transition zone
05:35 was not just a minute's walk for minerals,
05:38 it was a real giant sponge
05:40 that enclosed an immense underground water reservoir.
05:43 This revolutionary discovery suggests
05:45 that huge amounts of water would be stored deep underground,
05:49 even if they do not form oceans as we know them.
05:53 Volcanoes help us learn more about them,
05:55 not only on our own planet,
05:57 but also on other worlds.
05:59 In the burning heart of the Poas volcano,
06:01 in Costa Rica, is the Caliente Laguna.
06:05 This hydrothermal crater lake
06:07 is one of the most arid environments on Earth.
06:10 It presents a cocktail of burning temperatures,
06:13 toxic metals and water so acidic
06:16 that it is capable of corroding metal.
06:18 Despite these extreme conditions,
06:20 some resistant microorganisms manage to thrive there.
06:24 Their remarkable survival capacity
06:26 has caught the attention of scientists,
06:28 because it could well contain signs of life on Mars.
06:32 Scientists study these extremophile microbes,
06:35 who have developed a multitude of genetic adaptations
06:38 to resist their hostile environment.
06:40 They have genes that help them treat sulfur,
06:43 iron, carbon and bioplastic granules.
06:47 These adaptations could be crucial
06:49 in environments as difficult as Mars.
06:52 The NASA's Perseverance rover
06:55 is currently exploring the edge of the G0 crater on Mars.
06:59 Previously, research was focused on the ancient river beds
07:04 and other river deltas.
07:06 However, the discovery of the Caliente Laguna
07:09 suggests that we should also look for life
07:12 in the remains of ancient Martian thermal springs,
07:15 which could have once offered the ideal conditions
07:18 of heat, water and energy,
07:20 which are considered essential to life.
07:22 Volcanoes can support life in many ways,
07:25 but they can also destroy it.
07:27 Researchers think that volcanic activity
07:29 would be one of the main causes
07:31 of at least 3 of the 5 mass extinctions on our planet.
07:34 Let's take the example of the extinction of dinosaurs,
07:37 often attributed to the Chicksulub meteorite,
07:40 but which could also have been caused
07:42 by a series of volcanic eruptions.
07:44 The consequences of these eruptions
07:46 can be truly terrifying.
07:48 The Tambora, located on the Indonesian island of Sumbawa,
07:51 erupted in 1815,
07:53 marking the most powerful eruption ever recorded.
07:56 This colossal eruption projected
07:58 between 33 and 46 cubic kilometers of material,
08:01 and it was so strong that the sound of the eruption
08:04 could be heard up to Sumatra,
08:06 more than 2600 km away.
08:08 Before this catastrophic eruption,
08:11 the Tambora had been asleep for centuries,
08:14 and its magmatic chamber had slowly cooled
08:17 and crystallized, accumulating immense pressure.
08:20 It was finally released
08:22 during a series of large-scale events,
08:24 which began on April 5, 1815,
08:27 culminating on April 10
08:29 with the emission of gigantic columns of ash
08:31 and stone dust into the atmosphere.
08:34 The consequences of the eruption were disastrous.
08:37 Tsunamis ravaged the surroundings,
08:39 and about 4,600 people died
08:41 from the immediate consequences of the eruption.
08:44 The ash falls affected the air quality
08:46 and the water sources in the region.
08:48 This event is known to have been
08:50 "the year without summer"
08:52 due to the large amount of sulfur dioxide
08:54 that the Tambora has released into the stratosphere.
08:57 This created a "sail of aerosols"
08:59 that reflected the sunlight,
09:01 considerably lowering the temperatures of the globe.
09:04 A similar phenomenon occurred 66 million years ago
09:08 during the extinction of dinosaurs,
09:10 when the sky darkened for months.
09:12 Of course, no one was there to see it.
09:15 But that's what's being told.