00:00It's the 15th of January, 2022, 4.47 p.m. local time.
00:06It will start any moment.
00:07Here.
00:08Do you feel these jolts?
00:10The South Pacific is about to experience one of the most powerful volcanic eruptions ever
00:15recorded by modern instruments.
00:18The eruption begins at Hanga Tonga Hanga Ha'api, an underwater volcano in the Tongan Archipelago.
00:26The eruption itself is enormous.
00:28Its volcanic explosivity index is at least VEI 5, with the maximum being 8.
00:34It's as powerful as such historic catastrophes as Mount St. Helens in 1980 and Mount Vesuvius
00:41in 79 CE.
00:43The eruption releases a staggering 2.4 cubic miles of volcanic material and sends over
00:50150 million tons of water vapor into the stratosphere.
00:54This amount of water vapor would have been enough to fill 58,000 Olympic swimming pools.
01:00Additionally, the eruption generates the fastest underwater currents ever recorded and triggers
01:05large tsunamis that struck areas as far as Peru, more than 6,200 miles away from the
01:13volcano.
01:14And it takes at least four lives, with even more missing.
01:18But the craziest thing is that just before the eruption, 15 minutes ahead of time, there
01:23was a kind of warning.
01:26But as it often happens, people simply missed them.
01:30Two seismic stations about 466 miles away from the volcano, which is pretty far for
01:35this kind of thing, picked it up.
01:38They figured out it was a Rayleigh wave, which is a type of seismic wave that moves along
01:42Earth's surface.
01:44This wave was caused by a fracture in the ocean floor, where magma and seawater started
01:49to interact under a lot of pressure.
01:52That's likely what triggered the eruption.
01:55The crazy thing is that normally volcanic seismic signals are pretty small and can only
02:00be detected close to the volcano.
02:02But this Rayleigh wave traveled way farther than usual and was much stronger.
02:08It means there had to be a massive amount of movement going on beneath the surface before
02:13the eruption.
02:15While people on the ground didn't feel it, those distant sensors picked it up.
02:19This discovery is great for identifying volcanic threats earlier in the future and for improving
02:25early warning systems.
02:27If scientists can detect these seismic precursors, they could give a heads up before an eruption
02:32happens.
02:33That would give people time to evacuate and reduce the chances of injuries or property
02:37damage, especially for underwater volcanoes like this one, which can also trigger fatal
02:43tsunamis.
02:45Now, the eruption was big, but its impact was mostly contained.
02:50However, this discovery underlines how important seismic data is for predicting and preparing
02:56for these disasters.
02:59Even though this precursor wasn't used to issue a warning during this eruption, the
03:03idea that we could use this kind of information in real time during future eruptions is really
03:08promising, especially for underwater eruptions, which apparently might give us more warning
03:14time than we thought.
03:17Even though we wouldn't have been able to hear that precursor warning signal, there
03:21is a sound so loud it could actually finish you.
03:24And while such sounds are incredibly rare, the loudest noise ever recorded was indeed
03:30fatal to those who were close enough.
03:35On 27 August 1883, the eruption of the Krakatoa volcano in Indonesia created the loudest noise
03:43ever measured.
03:44It's thought to have been an astonishing 310 decibels at the source.
03:49To put this in perspective, a hand drill produces the sound of 98 decibels, the noise produced
03:56by a jet engine measures 140 decibels, and the sound of 180 decibels is capable of destroying
04:03your hearing tissue.
04:05So the sound Krakatoa produced reached more than 170 decibels at a distance of 100 miles,
04:13and sailors aboard a ship just 40 miles from the eruption had their eardrums burst from
04:18the sound.
04:20The explosion's reverberation was so powerful that it was heard 3,000 miles away.
04:26In fact, at a farm in Alice Springs, Australia, over 2,200 miles away, sheep farmers reported
04:33hearing what they thought were gunshots.
04:36The sound from Krakatoa traveled around the world multiple times.
04:40Although no one heard the explosion beyond 3,000 miles, spikes of atmospheric pressure
04:45were recorded in places as far away as Canada and England.
04:50Those must have been the sound waves produced by the eruption traveling around the globe.
04:58Sound above 150 decibels can potentially cause life-threatening harm.
05:02In particular, sounds between 170 and 200 decibels can result in lethal conditions,
05:09including burst lungs.
05:12Anything over 240 decibels could cause fatal injuries, and you don't even want to know
05:17what those are.
05:18I'll just say that those sometimes happen to cartoon characters, but rarely to people.
05:24The scientific explanation behind this is that sound is essentially a wave of pressure
05:29which can travel through both solids and liquids, and, in the case of an incredibly loud sound,
05:36pass right through the human body.
05:38If the pressure from such a sound is high enough, it can rupture eardrums and internal
05:42organs, causing significant, and often fatal, damage.
05:49Now you probably know how volcanoes sometimes have small earthquakes before they erupt.
05:54Well, they often produce this weird sound called a harmonic tremor.
05:59The sound kind of hums, and the frequency of the hum gets higher and higher until it
06:04suddenly stops just before the volcano erupts.
06:07The sound has been recorded at a bunch of volcanoes around the world, but the thing
06:12about Redoubt Volcano in Alaska is that its tremor is so intense people can actually hear
06:18it.
06:19It's like the volcano is letting out this crazy scream right before the eruption.
06:25According to a geophysicist at the University of Washington, the frequency of Redoubt's
06:30harmonic tremor is so high that it is barely perceptible as a low bass hum, and that's
06:36at its highest pitch.
06:38All because the pitch of Redoubt's tremor exceeds that of any other recorded volcano.
06:43It questions the limits of the existing models used to explain these phenomena.
06:48That's why researchers had to propose a new model to account for these unusually high-pitched
06:53tremors.
06:55Most volcanoes produce sound when magma bubbles vibrate as they rise through cracks in Earth's
07:00crust.
07:01But in the case of Redoubt, scientists believe that the harmonic tremor and associated earthquakes
07:06occur when magma is forced through a narrow opening under immense pressure.
07:11The thick magma sticks to the rock surface inside the conduit, a channel or a pipe that
07:16carries magma from a reservoir or chamber to the vent.
07:20As the pressure builds, the magma moves upward.
07:23This makes it stick again, until the pressure forces it to move once more.
07:27These sudden movements cause small earthquakes, which as the pressure increases, occur more
07:33rapidly and blend into a continuous, rising noise.
07:37So it's actually the rocks making the sounds.
07:41This new model is important, because it could help scientists better understand the eruptive
07:45cycles of volcanoes like Redoubt.
07:48It could also serve as a limited early warning system.
07:51By the time Redoubt began to scream like this, the volcano had already been erupting for
07:56a few days, so the tremor might only provide a few minutes or hours of warning before the
08:02next explosion.
08:03The harmonic tremor at Redoubt reaches an extremely high frequency, then falls eerily
08:09silent before the volcano erupts again.
08:12This pause occurs when the earthquake activity slows down and the two sides of the fault
08:17slip smoothly against one another.
08:19Maybe that's when even earthquakes can't keep up anymore.
08:23The new model may also apply to other volcanoes, such as the Soufrière Hills volcano on the
08:28Caribbean island of Montserrat.
08:32The research team is now planning to investigate why the pressure at Redoubt is concentrated
08:36in one specific spot.
08:38To move ahead in their research, the scientists have created two recordings of Redoubt's seismic
08:43activity.
08:44The first, a 10-second recording, compresses about 10 minutes of seismic sounds and harmonic
08:49tremors, sped up 60 times.
08:53The second, a 1-minute recording, condenses roughly an hour of activity, including more
08:58than 1,600 small earthquakes that had occurred before Redoubt's first explosion with harmonic
09:04tremor.
09:05These recordings could provide crucial insight into the dynamics of volcanic eruptions and
09:10the signals that precede them.
09:13That's it for today!
09:16So hey, if you pacified your curiosity, then give the video a like and share it with your
09:20friends!
09:21Or if you want more, just click on these videos and stay on the Bright Side!
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