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These alarming scenarios highlight the potential risks that could disrupt life as we know it, from devastating oceanic disasters to dams that threaten to flood entire cities. Understanding these dangers is crucial to preparing for a safer future.
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00:00The snowpack over your head splits in two right in front of your eyes and starts tumbling down in the
00:06frozen 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.
00:20But what if I tell you about another kind of avalanche, no less blood-chilling than the mountain one?
00:25And the most bizarre thing about it is that it occurs underwater.
00:31Underwater avalanches are powerful and disastrous natural phenomena, often much more dangerous than land ones.
00:38They have the potential to wreak havoc on the entire planet, leading to catastrophic consequences.
00:44The most alarming thing?
00:46They occur all the time under the surface of the ocean, impossible to see, predict, and extremely difficult to measure.
00:54Such avalanches can get 100 times larger than land ones, and they pose a great risk to the world's communications,
01:02capable of leaving the entire planet without the Internet.
01:06But we'll talk about it a bit later.
01:08First, 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 impact of a ginormous underwater
01:21avalanche.
01:21It started as a quite small underwater landslide in the Agadir Canyon.
01:28At first, it was just 0.35 cubic miles of material.
01:32But in no time, this mass increased more than 100 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 out all forms of animal and
01:54plant life on its way.
01:56The disastrous flow was so powerful that it literally eroded a 250-mile stretch of the canyon,
02:02cutting hundreds of feet into its sides and damaging a total area of 1,740 square miles.
02:09That'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 canyon walls
02:21to heights of up to 430 feet.
02:25Before scientists discovered the evidence of this catastrophic event,
02:29they had seriously underestimated the scale of destruction caused by submarine avalanches.
02:35By the way, these devastating catastrophes can start not only far away in the ocean, but also at estuaries.
02:48A turbidity current, a rapid, downhill flow of water containing a lot of sediment,
02:54rushed more than 680 miles from the Congo River estuary in the deep sea.
02:59This current appeared due to two factors.
03:03Terrible flooding along the Congo River in late December 2019, and unusually large spring tides.
03:09This resulted in an avalanche of sand and mud.
03:13Its volume was equivalent to one-third of all the sediment produced annually by all the rivers in the world.
03:19This sediment avalanche accelerated, increasing in speed from 17 feet per second in the upper part of the Congo Canyon
03:26to 26 feet per second when it reached the end of the channel, almost 700 miles away from the coastline.
03:33This route made it the longest avalanche of sediment ever measured on our planet.
03:38Two days later, the flow reached the deep ocean.
03:41The avalanche broke two seabed telecommunication cables, cutting internet data speeds all the way across West, Central, and South Africa.
03:52Now, before this disaster, scientists considered that measuring powerful deep sea avalanches was impractical.
04:00But the sediment flow in the Congo Canyon could be monitored directly,
04:04finally allowing researchers to assess how major river floods connected to the deep sea.
04:09They also concluded that how often underwater avalanches occurred depended on where the observer was.
04:17Seafloor canyons that are close to river mouths can experience several tiny avalanches per year.
04:22Other systems, far from river discharges like the Agadir Canyon, can only have one monster of an avalanche every 10
04:30,000 years or so.
04:33You're likely wondering, what can trigger an avalanche under the surface of the ocean?
04:37Well, earthquakes, typhoons, high tides, river floods, and even volcanic eruptions.
04:44And 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 do they relate to
04:56the scale of the event.
04:58See for yourself.
04:59In 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 a tiny underwater avalanche.
05:15And in 1929, a large earthquake off the coast of Newfoundland, Canada, triggered the largest underwater avalanche ever recorded.
05:23The 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 along the coastline.
05:42Now, submarine avalanches are totally invisible because they happen deep under the ocean's surface, which makes them extremely hard to
05:50study.
05:50But we must find a way, because these flows are super important.
05:55They 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 managed to reconstruct a massive
06:20submarine avalanche.
06:21It 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.
06:30But it quickly evolved into a colossal avalanche that grew to more than 650 feet tall.
06:38To put that into perspective, imagine a skyscraper-sized avalanche zooming from Liverpool to London,
06:45cutting a trench 100 feet deep and 9 miles wide.
06:50Then, it spread out over an area bigger than the UK, covering it with several feet of sand and mud.
06:57That's like burying a whole country.
07:00These findings are actually a big deal, because they show that even a small underwater landslide can turn into something
07:07massive and super destructive.
07:10But 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.
07:26That's enough to wrap around our planet 35 times.
07:30When a submarine avalanche breaks seafloor cables, the effects are usually super expensive and devastating.
07:37For example, in 2006, an earthquake in Taiwan triggered underwater avalanches that cut loads of seafloor cables connecting Southeast Asia
07:47with the rest of the world.
07:48The largest internet operator in China had a 90% loss of traffic to the USA at the peak of
07:55the event.
07:55As for Taiwan itself, it experienced between 74% to 100% loss in traffic to neighboring islands.
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 full picture of how they actually behaved.
08:22The new research focused on how underwater flows interacted with mini-basins, natural features on the ocean floor that look
08:30like shallow bowls.
08:31Despite being called mini, these bowls can be huge, up to 4 square miles.
08:39When turbidity currents flow into these mini-basins, they don't just stop.
08:44No, they hit the far side and curl back around like water eddies in a stream.
08:49These 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.
09:00If the basin is big and the current is slow, it starts to fill up with sediment.
09:05But if you crank up the flow speed or shrink the basin, the current starts to overflow, spilling over the
09:11basin.
09:13To study all this, the researchers created a mini-version of a mini-basin in a pool and used different
09:19speeds of flow to simulate turbidity currents.
09:22They even made their own sediment mixers to see how different sizes of particles would behave.
09:27In the end, they managed to mimic real-life ocean conditions, but on a smaller, manageable scale.
09:33Pretty cool, huh?
09:36The concrete of gigantic construction is cracking, barely keeping thousands of tons of water under control.
09:43That's when a tiny quake shakes the ground.
09:46It becomes a game-changer.
09:48The old dam gives up.
09:50An enormous amount of water dashes through the rapidly growing ruptures, pressing on the crumbling wall of stone.
09:57Another moment, and the huge dam disappears among powerful waterfalls, rushing toward the village down in the valley.
10:05When a large dam hits 50 years old, it reaches its alert age.
10:09But it's basically a warning that maintaining the dam is going to get much harder, and the risk factor starts
10:15going up.
10:16A recent study by the UN Institute for Water, Environment, and Health discovered that the UK and Japan have the
10:23most dams in this alert age category.
10:27No wonder.
10:28In both countries, the average dam is over 100 years old.
10:32If you, like me, are wondering why so many dams are getting old at the same time, the answer is
10:39pretty simple.
10:39Back in the middle of the 20th century, there was a massive dam-building boom.
10:44In the late 1950s through the 1970s, countries built over 1,100 dams every year.
10:51But after 1990, the construction frenzy slowed down.
10:55No more than 500 new dams appeared every year.
10:58And since 2000, this number has dropped even more, to below 300.
11:04But the huge problem is that many of the dams built during that mid-century boom are all aging at
11:10the same time.
11:11And a lot of countries are facing infrastructure problems at the moment.
11:15Because what happens when these dams get too old?
11:18If they're not maintained, they're likely to start to fail.
11:22And that's a real disaster.
11:24Both for water supplies and safety.
11:27It's like a ginormous water-based game of Jenga.
11:30And like in the real thing, we need to make sure those pieces don't fall.
11:37A disaster like the one we're talking about happened to the Bansha'a Dam built in 1952.
11:43This structure collapsed in 1975 after catastrophic rains from Typhoon Nina, leading to the loss of up to 240,000
11:53lives.
11:54One of the reasons was the dam's poor design.
11:57It wasn't built to withstand extreme conditions.
11:59So, when the region faced unprecedented downpours, the dam overflowed and collapsed.
12:06I bet you're now super eager to know whether that dam near your home is going to fail.
12:11Well, if you find it on our list of the world's most dangerous dams, maybe it's time to relocate.
12:17The Hoover Dam is one of the highest dams in the USA, standing on the Colorado River at the border
12:25between Nevada and Arizona.
12:27Towering at over 726 feet, it's a stunning sight, as well as a powerhouse of energy.
12:34Its base is as thick as two soccer fields are long, and each spillway can handle the volume of water
12:40that flows over Niagara Falls.
12:42But, experts warn that if the gigantic Hoover Dam breaks down, it'll most likely lead to catastrophic consequences, putting millions
12:51of lives at risk.
12:53The problem is, the dam is getting old.
12:56Plus, it's located in a seismically active area.
13:01The Almendra Dam is the highest dam in Spain.
13:05It was constructed between 1963 and 1970, and its main purpose is to control the flow of the River Tormez.
13:13This dam is no joke.
13:15Just a small manipulation could unleash a wave of destruction.
13:20So, it's actually a serious concern for those living downstream.
13:26The Jinping Dam, often referred to as the Jinping First Cascade, is the tallest dam in the world.
13:33Its height is 1,001 feet.
13:36You'll find it in China.
13:38It was constructed to regulate the flow of the Yedlong River.
13:42This structure carries immense responsibility, producing between 16 and 18 billion kilowatt-hours annually.
13:50The average U.S. household consumes about 11,000 kilowatt-hours per year.
13:56It means that the energy produced by the Jinping Hydropower Station is enough to supply around 1.6 million households.
14:04The Kariba Dam is a colossal structure built on the Zambezi River between Zambia and Zimbabwe.
14:11Multiple authorities carry out its maintenance.
14:13But, according to reports, if repairs are not conducted as soon as possible, the dam could lead to terrible destruction
14:20in the surrounding regions.
14:22It's crucial to keep an eye on this giant.
14:26The Mosul Dam is one of the most dangerous dams in the world.
14:30It's constructed of loose mud instead of concrete.
14:33This design mishap has led to ongoing erosion.
14:36The mud gets washed away by the river slowly and steadily.
14:41People work around the clock to repair and maintain the dam, but it's still a crucial site of concern.
14:48The Iduki Dam, located in Kerala, India, is a magnificent, double-curvature arch dam standing on the Periyar River.
14:56It's one of the highest arch dams in Asia, and it holds a huge volume of water.
15:01If a problem occurs at this dam, the consequences will be tragic for large areas.
15:06Such a disaster is likely to wipe out countless lives.
15:10So, the upkeep of the dam is crucial for everyone's safety.
15:16The Three Gorges Dam in China is one of the largest dams in the world, and the world's biggest hydroelectric
15:22power station, completed in 2012.
15:25The dam is nearly 600 feet tall and stretches for 7,660 feet.
15:30That's more than half the width of Manhattan.
15:33The construction is so huge and powerful that experts say it's even had serious impacts on Earth itself.
15:41For example, affecting the rotation of our planet.
15:45However great it is, this dam poses a serious risk to the environment and safety.
15:51For one thing, it was built in an earthquake-prone area.
15:54Yikes!
15:56Plus, sediment buildup in the reservoir might make the construction less stable.
16:01Also, when they were building this dam, they had to relocate over a million people and significantly change the ecosystem.
16:09Famous for its beauty
16:11The Monticello Dam in the USA attracts thousands of visitors each year.
16:16One of the reasons people are so eager to come there is its captivating glory hole.
16:21Indeed, at first sight, it may look like a picturesque feature.
16:26But in reality, this glory hole is actually a doorway to danger.
16:31It's basically a giant concrete funnel sticking up out of the dam.
16:35When the lake's surface level rises over 440 feet above sea level, which is close to overflowing the dam,
16:42the water starts draining out through the funnel as if from a bathtub.
16:46It creates a hypnotizing swirl, but you wouldn't want to get too close and get lost in the process.
16:53Nestled on the Columbia River in Washington, the Grand Coulee Dam has been powering the Pacific Northwest since 1942.
17:01It contains nearly 12 million cubic yards of concrete, which is enough to build a sidewalk 4 feet wide and
17:084 inches thick and wrap it twice around the equator.
17:10But this magnificent structure has some worries, too.
17:14It's an aging structure, and at over 80 years old, it needs lots of TLC.
17:20It's located in a seismically active zone, which brings its stability into question.
17:26The Kurobe Dam in Japan is a stunning 610 feet tall.
17:31It was finished in 1963, so the structure is already pretty old.
17:36Japan's earthquakes makes this dam a bit nervous, too.
17:39And last but not least, the area is prone to heavy rainfall.
17:44Intense rain might put extra pressure on the structure.
17:48On the Indus River, the Tarbella Dam is the largest earth-filled dam in the world.
17:54It was completed in 1976.
17:57Its issues include sediment buildup, which reduces its storage capacity.
18:01Plus, climate change has altered water flow, threatening the stability of the dam.
18:07The main reason we build dams is for irrigation.
18:10They help get water to our crops, and a whopping 40% of the food we eat around the globe
18:15depends on these big water-holding structures.
18:20Next on the list is hydropower.
18:22Dams are like giant batteries, turning flowing water into electricity.
18:27Then we have water supply, flood control, and even such fun activities as boating and fishing.
18:32But since dams are getting older, something needs to be done to protect people living close to them.
18:38The U.S. is leading the way in something called dam removal, having taken down more than 1,200 dams
18:45in the last 30 years.
18:46Old dams are not only risky, but also expensive to maintain.
18:50So taking them down is often the smartest and cheapest move.
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