- 10 時間前
Catastrophic Disasters That Could Alter Our World
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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?
00:45They 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.
01:27At 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.
01:55The 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.
02:43Let's go back to 14 January 2020 and see for ourselves.
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,
03:02terrible flooding along the Congo River in late December 2019 and unusually large spring tides.
03:09This resulted in an avalanche of sand and mud.
03:12Its volume was equivalent to one-third of all the sediment produced annually by all the rivers in the world.
03:19This sediment avalanche accelerated,
03:22increasing 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,
03:30almost 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.
03:42The avalanche broke two seabed telecommunication cables,
03:46cutting internet data speeds all the way across West, Central, and South Africa.
03:52Now, before this disaster,
03:55scientists 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.
04:10They also concluded that how often underwater avalanches occurred
04:14depended on where the observer was.
04:17Seafloor canyons that are close to river mouths can experience several tiny avalanches per year.
04:23Other systems, far from river discharges like the Agadir Canyon,
04:27can only have one monster of an avalanche every 10,000 years or so.
04:33You're likely wondering,
04:34what 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,
04:55nor do they relate to the 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.
05:06Tens of thousands of people lost their lives during that disaster.
05:11But it only triggered a tiny underwater avalanche.
05:15And in 1929, a large earthquake off the coast of Newfoundland, Canada,
05:19triggered the largest underwater avalanche ever recorded.
05:23The flow traveled at a speed of 42 miles per hour, carrying boulders, sand, and mud.
05:29It snapped 11 seabed cables on its journey downhill.
05:34The avalanche was so powerful,
05:36it produced a tsunami that claimed the lives of 28 people along the coastline.
05:42Now, submarine avalanches are totally invisible
05:45because they happen deep under the ocean's surface,
05:48which makes them extremely hard to study.
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.
06:00So, 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,
06:15which is a fancy word for ocean mapping,
06:17they managed to reconstruct a massive submarine 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,
06:40imagine a skyscraper-sized avalanche zooming from Liverpool to London,
06:45cutting a trench 100 feet deep and 9 miles wide.
06:50Then, it's spread out over an area bigger than the UK,
06:54covering it with several feet of sand and mud.
06:57That's like burying a whole country.
07:00These findings are actually a big deal,
07:03because they show that even a small underwater landslide
07:06can turn into something massive and super destructive.
07:10But that's not the worst.
07:12Think about undersea internet cables,
07:14which are essential for global communication.
07:16There 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,
07:33the effects are usually super expensive and devastating.
07:37For example, in 2006,
07:40an earthquake in Taiwan triggered underwater avalanches
07:43that cut loads of seafloor cables
07:45connecting Southeast Asia with the rest of the world.
07:48The largest internet operator in China
07:51had a 90% loss of traffic to the USA at the peak of the event.
07:55As for Taiwan itself,
07:57it 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,
08:18which didn't give the full picture of how they actually behaved.
08:22The new research focused on how underwater flows interacted with mini basins,
08:27natural features on the ocean floor that look like shallow bowls.
08:31Despite being called mini,
08:33these bowls can be huge,
08:36up to 4 square miles.
08:39When turbidity currents flow into these mini basins,
08:42they don't just stop.
08:44No, they hit the far side and curl back around
08:47like water eddies in a stream.
08:49These swirling flows move the sediment around
08:52before it settles on the ocean floor.
08:55The size of the mini basin
08:57and the speed of the flow can change how the current behaves.
09:00If the basin is big and the current is slow,
09:03it starts to fill up with sediment.
09:05But if you crank up the flow speed or shrink the basin,
09:09the current starts to overflow,
09:10spilling over the basin.
09:13To study all this,
09:14the researchers created a mini version of a mini basin in a pool
09:18and used different speeds of flow
09:19to simulate turbidity currents.
09:22They even made their own sediment mixers
09:24to see how different sizes of particles would behave.
09:27In the end,
09:28they managed to mimic real-life ocean conditions,
09:31but on a smaller, manageable scale.
09:34Pretty cool, huh?
09:35The concrete of gigantic construction is cracking,
09:39barely keeping thousands of tons of water under control.
09:42That'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
09:51dashes through the rapidly growing ruptures,
09:54pressing on the crumbling wall of stone.
09:57Another moment,
09:58and the huge dam disappears
10:00among powerful waterfalls,
10:02rushing toward the village down in the valley.
10:04When a large dam hits 50 years old,
10:07it reaches its alert age.
10:09But it's basically a warning
10:10that maintaining the dam
10:11is going to get much harder,
10:13and the risk factor starts going up.
10:16A recent study by the UN Institute for Water,
10:19Environment, and Health
10:21discovered that the UK and Japan
10:23have the most dams in this alert age category.
10:27No wonder.
10:28In both countries,
10:29the average dam is over 100 years old.
10:32If you, like me,
10:34are wondering why so many dams
10:36are getting old at the same time,
10:38the answer is pretty simple.
10:39Back in the middle of the 20th century,
10:42there was a massive dam building boom.
10:44In the late 1950s through the 1970s,
10:48countries built over 1,100 dams every year.
10:51But after 1990,
10:52the construction frenzy slowed down.
10:55No more than 500 new dams appeared every year,
10:58and since 2000,
11:00this number has dropped even more.
11:02To below 300.
11:04But the huge problem
11:05is that many of the dams built
11:07during that mid-century boom
11:09are all aging at the same time.
11:11And a lot of countries
11:12are facing infrastructure problems at the moment.
11:15Because what happens
11:16when these dams get too old?
11:18If they're not maintained,
11:20they'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.
11:31And like in the real thing,
11:32we need to make sure those pieces don't fall.
11:37A disaster like the one we're talking about
11:39happened to the Bancha'a Dam built in 1952.
11:43This structure collapsed in 1975
11:45after catastrophic rains from Typhoon Nina,
11:49leading to the loss of up to 240,000 lives.
11:54One of the reasons was the dam's poor design.
11:57It wasn't built to withstand extreme conditions.
12:00So, when the region faced unprecedented downpours,
12:03the dam overflowed and collapsed.
12:06I bet you're now super eager to know
12:08whether that dam near your home is going to fail.
12:11Well, if you find it on our list
12:13of the world's most dangerous dams,
12:15maybe it's time to relocate.
12:18The Hoover Dam is one of the highest dams in the USA,
12:22standing on the Colorado River
12:24at the border between Nevada and Arizona.
12:27Towering at over 726 feet,
12:30it's a stunning sight,
12:32as well as a powerhouse of energy.
12:34Its base is as thick as two soccer fields are long,
12:37and each spillway can handle the volume of water
12:40that flows over Niagara Falls.
12:42But experts warn that
12:44if the gigantic Hoover Dam breaks down,
12:47it'll most likely lead to catastrophic consequences,
12:50putting millions of 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,
13:09and its main purpose is to control the flow of the river torment.
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,
13:31is 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.
13:41This structure carries immense responsibility,
13:45producing between 16 and 18 billion kilowatt-hours annually.
13:51The average U.S. household consumes about 11,000 kilowatt-hours per year.
13:56It means that the energy produced by the Jinping Hydropower Station
13:59is enough to supply around 1.6 million households.
14:04The Kariba Dam is a colossal structure
14:07built on the Zambezi River between Zambia and Zimbabwe.
14:10Multiple authorities carry out its maintenance,
14:13but according to reports,
14:15if repairs are not conducted as soon as possible,
14:18the dam could lead to terrible destruction in 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,
14:44but it's still a crucial site of concern.
14:48The Iduki Dam, located in Kerala, India,
14:51is a magnificent, double-curvature arch-dam standing on the Periyar River.
14:56It's one of the highest arch-dams in Asia,
14:59and it holds a huge volume of water.
15:01If a problem occurs at this dam,
15:03the consequences will be tragic for large areas.
15:07Such 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,
15:20and the world's biggest hydroelectric power station,
15:23completed 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,
15:36that 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,
15:46this dam poses a serious risk to the environment and safety.
15:50For one thing, it was built in an earthquake-prone area.
15:54Yikes!
15:56Plus, sediment buildup in the reservoir
15:58might make the construction less stable.
16:01Also, when they were building this dam,
16:03they had to relocate over a million people
16:06and significantly change the ecosystem.
16:09Famous for its beauty
16:11The Monticello Dam in the USA
16:13attracts thousands of visitors each year.
16:16One of the reasons people are so eager to come there
16:19is its captivating glory hole.
16:21Indeed, at first sight,
16:23it may look like a picturesque feature.
16:26But in reality,
16:27this glory hole is actually a doorway to danger.
16:31It's basically a giant concrete funnel
16:33sticking up out of the dam.
16:35When the lake's surface level
16:36rises over 440 feet above sea level,
16:40which is close to overflowing the dam,
16:42the water starts draining out through the funnel
16:44as if from a bathtub.
16:46It creates a hypnotizing swirl,
16:48but you wouldn't want to get too close
16:50and get lost in the process.
16:53Nestled on the Columbia River in Washington,
16:56the Grand Coulee Dam
16:57has been powering the Pacific Northwest since 1942.
17:01It contains nearly 12 million cubic yards of concrete,
17:05which is enough to build a sidewalk
17:064 feet wide and 4 inches thick
17:08and wrap it twice around the equator.
17:11But this magnificent structure
17:12has some worries too.
17:14It's an aging structure,
17:16and at over 80 years old,
17:18it needs lots of TLC.
17:20It's located in a seismically active zone,
17:23which brings its stability into question.
17:26The Kurobe Dam in Japan
17:28is a stunning 610 feet tall.
17:31It was finished in 1963,
17:33so the structure is already pretty old.
17:36Japan's earthquakes
17:37makes this dam a bit nervous too.
17:40And last but not least,
17:42the area is prone to heavy rainfall.
17:44Intense rain might put extra pressure on the structure.
17:48On the Indus River,
17:50the Tarbella Dam
17:51is the largest earth-filled dam in the world.
17:54It was completed in 1976.
17:57Its issues include sediment buildup,
17:59which reduces its storage capacity.
18:01Plus, climate change has altered water flow,
18:04threatening the stability of the dam.
18:07The main reason we build dams is for irrigation.
18:10They help get water to our crops,
18:12and 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,
18:24turning flowing water into electricity.
18:27Then we have water supply,
18:29flood control,
18:29and even such fun activities as boating and fishing.
18:32But since dams are getting older,
18:35something needs to be done
18:36to protect people living close to them.
18:38The U.S. is leading the way
18:40in something called dam removal,
18:42having taken down more than 1,200 dams
18:44in the last 30 years.
18:46Old dams are not only risky,
18:48but also expensive to maintain.
18:50So taking them down
18:52is often the smartest and cheapest move.
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