The deep-sea 'emergency service' that keeps the internet running
Ninety-nine percent of the world's digital communications rely on subsea cables. When they break, it could spell disaster for a whole country's internet. How do you fix a fault at the bottom of the ocean?
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There are 1.4 million km (870,000 miles) of telecommunication cables on the seafloor, covering every ocean on the planet. Laid end to end, these cables would span the diameter of the Sun, and are responsible for the transfer of 99% of all digital data. But for something so important, they are surprisingly slender - often little more than 2cm in diameter, or about the width of a hosepipe.
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Since the first cables were laid in the 19th Century, they have been exposed to extreme environmental events, from submarine volcanic eruption to typhoons and floods. But the biggest cause of damage is not natural.
Most faults, with figures varying 70-80% depending on where you are in the world, relate to accidental human activities like the dropping of anchors or dragging of trawler boat nets, which snag on the cables, says Stephen Holden, head of maintenance for Europe, the Middle East and Africa at Global Marine, a subsea engineering firm who respond to subsea cable repairs. These usually occur in depths of 200-300m (but commercial fishing is increasingly pushing into deeper waters - in some places, 1,500m in the Northeast Atlantic). Only 10-20% of faults worldwide relate to natural hazards, and more frequently relate to cables wearing thin in places where currents cause them to rub against rocks, causing what are called "shunt faults", says Holden.
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In some places, climate change is making matters more challenging. Floods in West Africa are causing an increase in canyon-flushing in the Congo River, which is when large volumes of sediment flows into a river after flooding. This sediment is then dumped out of the river mouth into the Atlantic and could damage cables. "We know now to lay the cable further away from the estuary," says McGovern.
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