undersea data cables -- 1/26/26

26 Jan 2026

undersea data cables -- 1/26/26

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Today's selection -- from The Web Beneath the Waves by Samanth Subramanian. The oceans of the world are now crisscrossed by millions of miles of data cables:

“In the abyssal depths of the ocean, a data cable is a scrawny, lightly clothed thing. Its core consists of fibers of glass, each no thicker than a human hair, through which light transmits information at roughly 125,000 miles per second. Around the fibers, there is first a casing of steel for protection, then another of copper to carry electricity to keep the light moving, and then a final sheath of nylon soaked in tar. All this swaddling may sound like plenty of protection, but the layers are all thin, and the final product is—to use the image I heard most often from people in the subsea cable industry—no fatter than a garden hose. Some veterans draw this comparison in tones of both guilt and marvel, as if they're ashamed of consigning this delicate thing to the sea and astonished that it performs (for the most part) as reliably and unfussily as it does.

“Beneath miles and miles of water, these cables sit on the sea floor, conducting 95 percent of all the world's internet traffic. Humans have laid 870,000 miles of fiber optic cables under the ocean, connecting and reconnecting the eyelets on our shorelines, lacing the earth tightly together. Cables set out from places like Crescent Beach in Rhode Island, Wall Township in New Jersey, and Island Park in New York, and end in places like Penmarch in France, Bilbao in Spain, and Bude in the United Kingdom. Cables run between Milton in Newfoundland and Nuuk in Greenland, and between Toamasina in Madagascar and Saint-Marie in Reunion, and between Tarakan and Manado in Indonesia. Among the shortest cables anywhere is the forty-one-mile tyke between the Isle of Man and Northern Ireland; among the longest is 2Africa, which spans 28,000 miles and has branches into too many countries to list here. One brief cable stretches between Guningtou in Taiwan and Dadeng Island in China, countries that otherwise want little to do with each other. Another cable starts in the state of Washington and lands in Alaska, because sometimes it's easier or cheaper to put down cable under the sea than over land. Longyearbyen, in Svalbard, has not one but two cables linking it to the Norwegian mainland. Even tiny St. Helena, population 4,439, got hooked up to an undersea cable in 2023. Cables have acronymic names like SAFE and AAE, or functional names like Greenland Connect and Pacific Crossing-a, or mythopoeic names like JUPITER and Honomoana, or historical names like Leif Erikson and Grace Hopper. There are roughly 550 such submarine cables around the planet, and more are being built every day. A Finnish company planned to spend a billion or so dollars to lay cable under the Arctic Ocean—a task made easier by how rapidly its ice cover is melting. Upon completion, the cable was designed to shave twenty to sixty milliseconds off the speed of trades made by banks in Tokyo and London. For now, Antarctica is the only major uncabled landmass on Earth, but it won't be for long. The US has plans.

World map showing submarine cables in 2015

“The cable that connects Tongatapu to Fiji and thence to the world, 515 miles long and part of a cable network called Southern Cross, was switched on in 2013. A 250-mile domestic cable between Tongatapu and the northern island of Vava'u began operating in 2018. In general, this pocket of the Pacific is a rough neighborhood for undersea cables. ‘Ideally, you'd route around seamounts—but what happens if your island itself is a volcano, as happens in the Caribbean or the Pacific?’ Clare said. ‘And if you're looking at standoff distances’—by which he meant the gap that a cable maintains between itself and a hazard—‘if you make your standoff distance one hundred kilometers in an area like this, you've already hit the next volcano.’ The cable could have been plotted to land not in the west of Tongatapu but in the east—but that would have meant negotiating a steep underwater slope with plenty of canyons and a reputation for earthquakes. ‘So that's a really gnarly place to lay a cable. You have to go with the least worst option.’”