Saviez-vous qu'il y a un immense océan souterrain caché sous nos pieds ? Les scientifiques viennent de découvrir ce qui pourrait être le plus grand réservoir d'eau souterrain de la Terre, enfoui à des centaines de kilomètres sous la surface. Cet océan caché n'est pas comme ceux que nous voyons : il est piégé à l'intérieur d'un type de roche spécial appelé ringwoodite, qui retient l'eau comme une éponge géante. En fait, il pourrait y avoir trois fois plus d'eau là-bas que dans tous les océans de surface réunis ! Cette découverte époustouflante pourrait changer notre compréhension du cycle de l'eau de la Terre et de l'origine de l'eau de notre planète. Qui sait, peut-être existe-t-il encore d'autres océans cachés qui attendent d'être découverts en profondeur ? Animation créée par Sympa.
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00:00Researchers have discovered the largest water reservoir in the Cascades chain, in Oregon.
00:06Hidden underground, it contains a volume of water more than double that of Lake Mead.
00:12To be precise, it contains at least 81 cubic kilometers of water,
00:16which is the equivalent of nearly 162 billion bottles.
00:20Due to a bottle per day, it would take you about 484 billion years to come to an end.
00:26It is therefore a surprising war that this discovery arouses so much enthusiasm.
00:30Spreading over about 1,100 kilometers, from Northern California to British Columbia,
00:35the Cascades chain houses the largest aquifer in the world.
00:39The high Cascades, located in Oregon, are made up of more recent volcanic rocks,
00:44aged about 8 million years, while the western Cascades, much older, date back 45 million years.
00:52They are distinguished by their deep canyons.
00:55Researchers have looked at the transition zone between these two formations,
00:59in order to analyze the circulation of water within the rock,
01:02and to study the evolution of volcanic processes over time.
01:06As part of this study, they measured the temperatures of the rocks at different depths.
01:11It was thus that they made the discovery of this immense underground aquifer.
01:16In principle, the temperature of the rocks increases with the depth,
01:19because they are close to the earth's core.
01:22However, in some areas, they remain surprisingly stable, even at great depths.
01:27This phenomenon indicates the presence of water circulating through the rock and cooling it.
01:32In other words, the Cascades act like a natural water castle,
01:36retaining and then gradually releasing water towards the rivers.
01:40These geological discoveries are of great importance for two reasons.
01:44On the one hand, they reveal an underground water reserve
01:47likely to become a strategic resource for the future.
01:50However, its evolution and its ability to resist environmental transformations remain uncertain.
01:56It is therefore essential to carry out in-depth research
02:00in order to ensure efficient and long-term management.
02:03In addition, volcanic activity is also influenced by this phenomenon.
02:07When water infiltrates deeply and reaches the magma,
02:11it evaporates instantly,
02:13generating extreme pressure that can cause explosive eruptions.
02:17A better understanding of the volume of water retained in the rock
02:20would allow us to anticipate these eruptions and assess the risks they pose.
02:24Although this discovery is fascinating, it still raises many questions.
02:29For example, how does this water circulate in the volcanic rock?
02:33What part of it is actually exploitable?
02:35This reservoir is fed by rainfall and snow melting.
02:39A succession of dry years could affect both water supply and the stability of the volcano.
02:45Researchers are working to better assess the extent of this phenomenon
02:48in order to ensure responsible management.
02:51Let us now look at the chain of waterfalls, a true geological wonder.
02:56Imagine a massive mountain mass stretching from North California to British Columbia,
03:01crossing Oregon in its heart.
03:03Just in this state, it extends over 420 km long and up to 150 km wide,
03:09covering nearly 44,000 km²,
03:12an area exceeding that of the nine smallest American states.
03:16What makes this chain even more impressive is that the part in Oregon
03:21was essentially shaped by volcanoes
03:24and contains at least one reservoir of prisoner water, volcanic rocks.
03:28It owes its existence to the subduction zone of Cascadia,
03:32where the tectonic plate Juan de Fuca,
03:34a fragment of terrestrial crust located under the Pacific Ocean,
03:38gradually sinks under North America.
03:41As it plunges, this plate undergoes extreme temperatures and pressures
03:45that expel the water contained in the oceanic rock.
03:48This phenomenon lowers the melting point of the terrestrial mantle,
03:51thus favoring the formation of magma.
03:53It then rises and feeds the volcanoes of the Cascades.
03:57This process takes place in the belt of fire,
03:59a vast volcanic network surrounding the Pacific,
04:02and illustrates the permanent dynamics of this gigantic geological system.
04:06The Cascades of Oregon are divided into two distinct groups.
04:09The Western Cascades and the High Cascades,
04:12which have very different characteristics.
04:15The Western Cascades, the oldest part,
04:18were formed about 45 million years ago.
04:22They are distinguished by a steep relief,
04:24deeply dug by the streams,
04:27some canyons reaching up to 1,100 meters deep.
04:31Once the seat of an intense volcanic activity,
04:34this region has since been shaped by erosion,
04:37which has gradually remodeled the landscape.
04:40Conversely, the High Cascades are much more recent
04:43and much less eroded.
04:45About 8 million years ago,
04:47the volcanic activity moved,
04:49causing new eruptions that filled old canyons
04:52and softened the relief.
04:54The continuous accumulation of lava
04:56prevented the rivers from digging valleys as deep
04:59as in the Western Cascades,
05:01giving this area a more homogeneous appearance.
05:03Thus, when comparing these two regions,
05:06one appears fractured and chaotic,
05:08while the other seems more uniform
05:10and edified by successive eruptions.
05:12It is in the High Cascades that some of the most
05:15emblematic volcanoes in Oregon are located,
05:17including Mount Hood, Mount Jefferson,
05:19the Three Sisters and Crater Lake.
05:22The latter is from the collapse of Mount Mazama
05:24after a gigantic eruption.
05:26Unlike the small volcanoes,
05:28which briefly emerge and spit a little lava
05:31before disappearing in a few years,
05:33these vast volcanic centers have been active
05:35for millennia.
05:37And because of their size,
05:39they house magmatic systems
05:41of great complexity.
05:43They produce a wide variety of magma,
05:45ranging from basalt, a fluid and fast lava,
05:48to andesite, dacite and rhyolite,
05:50the latter being responsible
05:52for the most violent eruptions.
05:54Thus, if some volcanoes are content
05:56to let lava flows escape,
05:58others are likely to cause
06:01explosions of devastating magnitude.
06:03Another fascinating aspect of these volcanoes
06:05with exceptional longevity
06:07is that their underground magmatic chambers
06:09retain their heat for an extremely long time.
06:12This is what makes the Cascades
06:14one of the best sites to exploit
06:16geothermal energy.
06:18A huge reserve of heat
06:20rests just below the surface,
06:22waiting to be used.
06:24Not to mention the volcanic water reservoir
06:26of the Cascades,
06:28one of the world's most explosive zones.
06:30Imagine a gigantic arch
06:32in the shape of an iron horse,
06:34encircling the Pacific Ocean
06:36for about 40,000 km.
06:38It is one of the most active regions
06:40of the globe,
06:42where the earth's tectonic plates
06:44constantly move,
06:46colliding and collapsing
06:48one under the other.
06:50This process is the origin
06:52of earthquakes,
06:54earthquakes and earthquakes.
06:56This process is the origin
06:58of earthquakes of unimaginable power,
07:00major volcanic eruptions
07:02and the formation of deep oceanic pits.
07:04The belt of fire
07:06follows the lines of contact
07:08between several plates,
07:10including the Eurasian,
07:12North American,
07:14Juan de Fuca,
07:16Cocos, Caribbean,
07:18Nazca, Antarctic,
07:20Indian, Australian and Philippine plates.
07:22They encircle the vast Pacific plate.
07:24The tectonic plates never remain still.
07:26They move continuously,
07:28colliding or sliding
07:30one under the other
07:32at the level of their borders,
07:34known as faults.
07:36This movement generates a diversity
07:38of spectacular phenomena.
07:40Abyssal pits with volcanoes
07:42and devastating earthquakes.
07:44One of the most impressive examples
07:46of this tectonic activity
07:48is the Marian pit,
07:50located east of Guam.
07:52It is the deepest oceanic pit in the world.
07:54It results from a phenomenon
07:56called subduction,
07:58in which one plate is forced
08:00to plunge under another,
08:02progressively sinking
08:04into the terrestrial mantle.
08:06The Marian pit remains
08:08one of the most enigmatic places
08:10on Earth.
08:12From a dizzying depth,
08:14it is subjected to crushing pressure
08:16and total darkness,
08:18which has long been believed
08:20In 2005, researchers
08:22have highlighted the existence
08:24of tiny unicellular organisms
08:26in the Challenger Deep,
08:28the deepest point of the Marian pit.
08:30They have also observed
08:32strange sea cucumbers
08:34as well as rock formations
08:36with unexpected shades.
08:38In addition, the pit houses
08:40hydrothermal chimneys,
08:42a real hot underwater source
08:44where water,
08:46despite extreme temperatures
08:48can be found.
08:50The Marian pit is also
08:52at the origin of 90%
08:54of the world's earthquakes.
08:56Some of the most devastating
08:58earthquakes in history
09:00took place there,
09:02notably the Valdivia earthquake
09:04in Chile in 1960,
09:06which holds the record
09:08of the most powerful ever recorded
09:10with a magnitude of 9.5
09:12on the Richter scale.
09:14But seismic activity
09:16is also at the origin
09:18of 75% of the world's volcanoes.
09:20Some of the most striking
09:22eruptions in history
09:24took birth there,
09:26like the terrible explosion
09:28of the Tambora in Indonesia.
09:30In short, the fire belt
09:32is among the most hostile
09:34regions of the globe.
09:36However, it remains
09:38an irresistible source
09:40of fascination.
09:42Who knows what major discoveries