00:00The snowpack over your head splits in two right in front of your eyes and starts tumbling
00:06down in the frozen slope to its resting place far, far below.
00:10Anything in its way is crushed under the immense mass of snow and debris.
00:15You're witnessing an avalanche, one of the most dangerous natural disasters.
00:21But what if I tell you about another kind of avalanche, no less blood-chilling than
00:24the mountain one?
00:26And the most bizarre thing about it is that it occurs underwater.
00:32Underwater avalanches are powerful and disastrous natural phenomena, often much more dangerous
00:37than land ones.
00:39They have the potential to wreak havoc on the entire planet, leading to catastrophic
00:43consequences.
00:44The most alarming thing?
00:46They occur all the time under the surface of the ocean, impossible to see, predict,
00:51and extremely difficult to measure.
00:55Such avalanches can get 100 times larger than land ones, and they pose a great risk
01:00to the world's communications, capable of leaving the entire planet without the internet.
01:06But we'll talk about it a bit later.
01:09First let's go 60,000 years back into the past.
01:13We're near the northwest coast of Africa, ready to witness the colossal scale and devastating
01:19impact of a ginormous underwater avalanche.
01:22It started as a quite small underwater landslide in the Agadir Canyon.
01:28At first it was just 0.35 cubic miles of material, but in no time this mass increased more than
01:36100 times in size while traveling across the Atlantic ocean floor.
01:41As the avalanche sped up and grew, it picked up gravel, sand, rocks, and mud.
01:47It carved a devastating path through one of the world's largest submarine canyons, wiping
01:52out all forms of animal and plant life on its way.
01:56The disastrous flow was so powerful that it literally eroded a 250 mile stretch of the
02:02canyon, cutting hundreds of feet into its sides and damaging a total area of 1,740 square
02:09miles.
02:10That's the area of more than three and a half New York cities!
02:15As for the force of the flow, it was so immense that it propelled massive boulders up the
02:20canyon walls to heights of up to 430 feet.
02:25Before scientists discovered the evidence of this catastrophic event, they had seriously
02:30underestimated the scale of destruction caused by submarine avalanches.
02:36By the way, these devastating catastrophes can start not only far away in the ocean,
02:41but also at estuaries.
02:44Let's go back to 14 January 2020 and see for ourselves.
02:49A turbidity current, a rapid, downhill flow of water containing a lot of sediment, rushed
02:55more than 680 miles from the Congo River estuary in the deep sea.
03:00This current appeared due to two factors, terrible flooding along the Congo River in
03:05late December 2019 and unusually large spring tides.
03:10This resulted in an avalanche of sand and mud.
03:13Its volume was equivalent to one third of all the sediment produced annually by all
03:17the rivers in the world.
03:20This sediment avalanche accelerated, increasing in speed from 17 feet per second in the upper
03:25part of the Congo Canyon to 26 feet per second when it reached the end of the channel, almost
03:30700 miles away from the coastline.
03:34This route made it the longest avalanche of sediment ever measured on our planet.
03:39Two days later, the flow reached the deep ocean.
03:43The avalanche broke two seabed telecommunication cables, cutting internet data speeds all the
03:48way across West, Central, and South Africa.
03:52Now, before this disaster, scientists considered that measuring powerful deep sea avalanches
03:59was impractical.
04:00But the sediment flow in the Congo Canyon could be monitored directly, finally allowing
04:05researchers to assess how major river floods connected to the deep sea.
04:10They also concluded that how often underwater avalanches occurred depended on where the
04:15observer was.
04:18Seafloor canyons that are close to river mouths can experience several tiny avalanches per
04:22year.
04:23Other systems, far from river discharges like the Agadir Canyon, can only have one monster
04:29of an avalanche every 10,000 years or so.
04:33You're likely wondering, what can trigger an avalanche under the surface of the ocean?
04:38Well, earthquakes, typhoons, high tides, river floods, and even volcanic eruptions.
04:45And due to our changing climate, such events become more and more frequent and intense.
04:50At the same time, these triggers don't mean that an avalanche is bound to happen, nor
04:55do they relate to the scale of the event.
04:58See for yourself.
05:00In 1755, a powerful earthquake hit the coast of Portugal, wiping out large parts of Lisbon.
05:07Tens of thousands of people lost their lives during that disaster, but it only triggered
05:12a tiny underwater avalanche.
05:15And in 1929, a large earthquake off the coast of Newfoundland, Canada triggered the largest
05:21underwater avalanche ever recorded.
05:24The flow traveled at a speed of 42 miles per hour, carrying boulders, sand, and mud.
05:30It snapped 11 seabed cables on its journey downhill.
05:34The avalanche was so powerful, it produced a tsunami that claimed the lives of 28 people
05:40along the coastline.
05:41Now, submarine avalanches are totally invisible because they happen deep under the ocean surface,
05:48which makes them extremely hard to study.
05:51But we must find a way, because these flows are super important.
05:56They transport sediments, nutrients, and even pollutants across the ocean floor.
06:01So, a research team from Liverpool decided to unravel this mystery.
06:06Over the last 40 years, they've collected more than 300 samples from the ocean floor.
06:12Combined with seismic and bathymetric data, which is a fancy word for ocean mapping, they
06:17managed to reconstruct a massive submarine avalanche.
06:22It was the first time an underwater avalanche of this size was mapped out.
06:26An even cooler thing, the event itself started off pretty modestly, but it quickly evolved
06:32into a colossal avalanche that grew to more than 650 feet tall.
06:39To put that into perspective, imagine a skyscraper-sized avalanche zooming from Liverpool to London,
06:46cutting a trench 100 feet deep and 9 miles wide.
06:51Then it spread out over an area bigger than the UK, covering it with several feet of sand
06:56and mud.
06:57That's like burying a whole country.
07:01These findings are actually a big deal, because they show that even a small underwater landslide
07:06can turn into something massive and super destructive.
07:11But that's not the worst.
07:12Think about undersea internet cables, which are essential for global communication.
07:17There are more than 550 active seafloor cables around the world.
07:22Their combined length is a whopping 870,000 miles.
07:27That's enough to wrap around our planet 35 times.
07:31When a submarine avalanche breaks seafloor cables, the effects are usually super expensive
07:36and devastating.
07:38For example, in 2006, an earthquake in Taiwan triggered underwater avalanches that cut loads
07:44of seafloor cables connecting Southeast Asia with the rest of the world.
07:49The largest internet operator in China had a 90% loss of traffic to the USA at the peak
07:54of the event.
07:56As for Taiwan itself, it experienced between 74 to 100% loss in traffic to neighboring
08:02islands.
08:04So now you probably get why we need to learn more about this natural phenomenon.
08:09Luckily, researchers at Tulane University have found a way to study it in 3D.
08:15Previous studies only looked at submarine avalanches in 2D, which didn't give the
08:20full picture of how they actually behaved.
08:23The new research focused on how underwater flows interacted with mini-basins, natural
08:28features on the ocean floor that look like shallow bowls.
08:32Despite being called mini, these bowls can be huge, up to 4 square miles.
08:40When turbidity currents flow into these mini-basins, they don't just stop.
08:45They hit the far side and curl back around, like water eddies in a stream.
08:50These swirling flows move the sediment around before it settles on the ocean floor.
08:55The size of the mini-basin and the speed of the flow can change how the current behaves.
09:01If the basin is big, and the current is slow, it starts to fill up with sediment.
09:06But if you crank up the flow speed or shrink the basin, the current starts to overflow,
09:11spilling over the basin.
09:13To study all this, the researchers created a mini-version of a mini-basin in a pool and
09:18used different speeds of flow to simulate turbidity currents.
09:22They even made their own sediment mixers to see how different sizes of particles would
09:27behave.
09:28In the end, they managed to mimic real-life ocean conditions, but on a smaller, manageable
09:33scale.
09:35Pretty cool, huh?
09:36That's it for today!
09:38So hey, if you pacified your curiosity, then give the video a like and share it with your
09:42friends.
09:43Or if you want more, just click on these videos and stay on the Bright Side!
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