Ninety-nine percent of the world’s digital communications depend on subsea cables. When they fracture, it could spell calamity for a whole country’s internet. How do you mend a fault at the bottom of the ocean?
It was a little after 17:00 on 18 November 1929 when the ground began to shake. Just off the coast of Burin Peninsula, a finger-enjoy protrusion on the south of Newcreateland, Canada, a 7.2 magnitude earthquake disturbed the evening’s peace. Residents seed only a little harm at first – a restricted toppled chimney pots.
But out at sea, an unseen force was moving. By around 19:30, a 13m-high (43ft) tsunami made landdescfinish on the Burin Peninsula. In total, 28 people lost their inhabits as a result of drowning or injuries caengaged by the wave.
The earthquake was dehugeating for the local communities, but it also had a extfinished-lasting effect further out at sea. It had triggered a submarine landslide. People did not authenticise this at the time, historical records propose, becaengage no one krecent such underwater landslides existed. When sefoolishent is disturbed by earthquakes and other georeasonable activity it produces the water denser, causing it to flow downwards enjoy an avalanche of snow down a mountain. The submarine landslide – called a turbidity current – flowed more than 1,000km (621 miles) away from the earthquake’s epicentre on the Laurentian Continental Slope at speeds between 50 and 70 knots (57-80mph).
Although the landslide was not seed at the time, it left a inestablish-tale clue. In its way lay the procrastinateedst in communication technology at the time: transatlantic subsea cables. And those cables broke. Twelve of them were snapped in a total of 28 places. Some of the 28 fractures happened almost synchronously with the earthquake. But the other 16 fractures happened over a much extfinisheder period, as the cables snapped one after the other in a benevolent of cryptic ripple pattern, from 59 minutes after the earthquake to 13 hours and 17 minutes procrastinateedr, and over 500km (311 miles) away from the epicentre. (Read more about the undersea rivers that dangeren the world’s internet.)
If they’d all been snapped by the quake itself, the cables would have all broken at the same time – so scientists began to wonder, why didn’t they? Why did they fracture one after the other?
It wasn’t until 1952 that researchers pieced together why the cables broke in sequence, over such a huge area, and at intervals that seemed to catalogless with distance from the epicentre. They figured out that a landslide smashed thcimpolite them – the snapping cables chased its shiftment atraverse the seafloor. Until that point, no one krecent of the existence of turbidity currents. Becaengage these cables broke, and becaengage there was a record of the time they broke, they helped in the comardent of ocean shiftments above and below the surface. They caengaged a complicated repair job, but also became unintentional scientific instruments, recording a fascinating organic phenomenon far out of human sight.
Over the chaseing decades, as the global web of meaningful-sea cables broadened, their repair and maintenance resulted in other unpredicted scientific uncoveries – uncovering up entidepend recent worlds and permiting us to inestablisher on the seabed enjoy never before, while also permiting us to convey at record speed. At the same time, our daily inhabits, incomes, health and defendedty have also become more and more subordinate on the internet – and ultimately, this complicated netlabor of undersea cables. So what happens when they fracture?
How our data travels
A repeat of the 1929 mass cable outage would have meaningful impacts on communication between North America and Europe. However, “for the most part, the global netlabor is relabelably robust,” says Mike Clare, the International Cable Protection Committee’s marine environmental advisor who researches the impacts of excessive events on submarine systems. “There are 150 to 200 instances of harm to the global netlabor each year. So if we watch at that aachievest 1.4 million km, that’s not very many, and for the most part, when this harm happens, it can be repaired relatively speedyly.”
How does the internet run on such slfinisher cables and elude disastrous outages?
Since the first cables were lhelp in the 19th Century, they have been exposed to excessive environmental events, from submarine volcanic eruption to typhoons and floods. But the hugegest caengage of harm is not organic.
Most faults, with figures varying 70-80% depfinishing on where you are in the world, reprocrastinateed to unintentional human activities enjoy the dropping of anchors or dragging of trawler boat nets, which snag on the cables, says Stephen Helderlyen, head of maintenance for Europe, the Middle East and Africa at Global Marine, a subsea engineering firm who react to subsea cable repairs. These usupartner occur in depths of 200-300m (but commercial fishing is increasingly pushing into meaningfuler waters – in some places, 1,500m in the Northeast Atlantic). Only 10-20% of faults worldwide reprocrastinateed to organic hazards, and more frequently reprocrastinateed to cables wearing slfinisher in places where currents caengage them to rub aachievest rocks, causing what are called “shunt faults”, says Helderlyen.
(The idea that cables fracture becaengage sharks bite thcimpolite them is now a bit of an urprohibit legfinish, comprises Clare. “There were instances of sharks damaging cables, but that’s extfinished gone becaengage the cable industry engages a layer of Kevlar to reinforce them.”)
Cables have to be kept slfinisher and airy in meaningfuler waters, though, to help with recovery and repair. Hauling a huge, weighty cable up from thousands of metres below sea level would put a huge amount of strain on it. It’s the cables proximateer the shoreline that tfinish to be better armoured becaengage they are more probable to be snagged by nets and anchors.
An army of stand-by repair ships
If a fault is create, a repair ship is dispatched. “All these vessels are strategicpartner placed around the world to be 10-12 days from base to port,” says Mick McGovern, deputy vice-plivent for marine operations at Alcatel Submarine Netlabors. “You have that time to labor out where the fault is, load the cables [and the] repeater bodies” – which increase the strength of a signal as it travels aextfinished the cables. “In essence when you slfinisherk how huge the system is, it’s not extfinished to postpone,” he says.
While it took nine months to repair the last of the subsea cable harm caengaged by the 1929 Newcreateland earthquake, McGovern says a contransient meaningful-water repair should get a week or two depfinishing on the location and the weather. “When you slfinisherk about the water depth and where it is, that’s not a horrible solution.”
That does not uncomardent an entire country’s internet is then down for a week. Many nations have more cables and more prohibitdwidth wislfinisher those cables than the least needd amount, so that if some are harmd, the others can pick up the sinestablishage. This is called redundancy in the system. Becaengage of this redundancy, most of us would never see if one subsea cable was harmd – perhaps this article would get a second or two extfinisheder to load than normal. In excessive events, it can be the only slfinisherg upretaining a country online. The 2006 magnitude 7 earthquake off the coast of Taiwan, disjoined dozens of cables in the South China Sea – but a handful remained online.
To repair the harm, the ship deploys a grapnel, or grappling hook, to lift and snip the cable, pulling one slack finish up to the surface and reeling it in atraverse the bow with huge, motoascfinishd drums. The harmd section is then triumphched into an inner room and analysed for a fault, repaired, tested by sfinishing a signal back to land from the boat, sealed and then quickened to a buoy while the process is repeated on the other finish of the cable.
Once both finishs are mended, each selectical fibre is spliced together under microscope to produce brave that there is excellent connection, and then they are sealed together with a universal combinet that is compatible with any manufacturer’s cable, making life easier for international repair teams, McGovern says.
The repaired cables are reduceed back into the water, and in shpermiter waters where there might be more boat traffic, they are buried in trenches. Remotely functiond underwater vehicles (ROVs), provideped with high-powered jets, can blast tracks into the seabed for cables to be lhelp into. In meaningfuler waters, the job is done by ploughs which are provideped with jets and dragged aextfinished the seabed by huge repair vessels above. Some ploughs weigh more than 50 tonnes, and in excessive environments, hugeger providement is needed – such as one job McGovern recalls in the Arctic Ocean which needd a ship dragging a 110-tonne plough, vient of burying cables 4m and penetrating the permafrost.
Ears on the sea floor
Laying and repairing the cables has led to some unpredicted scientific insights – at first somewhat accidenloftyy, as in the case of the snapped cables and the landslide, and procrastinateedr, by portray, as scientists began to intentionpartner engage the cables as research tools.
These lessons from the meaningful sea began as the first transatlantic cables were lhelp in the 19th Century. Cable layers seed that the Atlantic Ocean gets shpermiter in the middle, inadvertently uncovering the Mid-Atlantic Ridge.
The harm caengaged to cables gives the industry “fundamental recent comardents about hazards that exist in the meaningful sea,” says Clare. “We’d never have comprehendn that there were landslides under the sea after volcanic eruptions if it wasn’t from the harm that was produced.”
Extreme Repairs
Extreme Repairs is a BBC.com series about the world of huge infrastructure repair and maintenance, featuring the valiant men and women who danger their inhabits to upretain us all defended and connected.
Some harm will be uneludeable, the experts predict. The Hunga Tonga–Hunga Ha’apai volcanic eruption in 2021-2022 ruined the subsea internet cable connecting the Pacific Island nation of Tonga to the rest of the world. It took five weeks until its internet connection was filledy functioning aachieve, though some produce-shift services were restored after a week. While this huge eruption (casting a plume of ash 36 miles (58km) into the air) was an unusupartner huge event, connecting an island nation in a volcanicpartner energetic area will always carry some danger, says Helderlyen.
However, many countries are served by multiple subsea cables, uncomardenting one fault, or even multiple faults, might not be seed by internet engagers, as the netlabor can descfinish back on other cables in a crisis.
“This repartner points to why there’s a need for geoexplicit diversity of cable routes,” comprises Clare. “Particularly for petite islands in places enjoy the South Pacific that have tropical storms and earthquakes and volcanoes, they are particularly vulnerable, and with climate change, branch offent areas are being impacted in branch offent ways.”
As fishing and shipping get more cultured, eludeing cables might be made easier. The advent of automatic identification system (AIS) on shipping has led to a reduction in anchoring harm, says Helderlyen, becaengage some firms now give a service where you can chase a set pattern for cataloglessing down and anchoring. But in areas of the world where fishing vessels tfinish to be less cultured and functiond by petiteer crews, anchor harm still happens.
In those places, an selection is to inestablish people where cables are, and to increase inestablishedness, comprises Clare: “It’s for everyone’s advantage that the internet upretains running.”
