What lies beneath The growing threat to the hidden network of cables that power the internet

It was the opening days of 2022, in the aftermath of a huge volcanic eruption, when Tonga went dark.

- Jonathan Yerushalmy

The underwater eruption - 1,000 times more powerful than the bomb that was dropped on Hiroshima - sent tsunami waves across Tonga's nearby archipelago and blanketed the island's white coral sands in ash.

The strength of the Hunga Tonga-Hunga-Ha'apai eruption severed internet connectivity with Tonga, causing a communication blackout at just the moment that a crisis was unfolding.

When the undersea cable that provides the country's internet was restored weeks later, the scale of the disruption was clear. The lack of connectivity had hampered recovery efforts, while at the same time devastating businesses and local finances, many of which depend on remittances from abroad. The disaster exposed the extreme vulnerabilities of the infrastructure that underpins the workings of the internet.

Contemporary life is really inseparable from an operational internet, said Nicole Starosielski, a professor at the University of California, Berkeley, and the author of The Undersea Network.

Modern consumers have come to imagine the internet as something unseen in the atmosphere - an invisible "cloud" just above our heads, raining data down upon us.

Because our devices aren't tethered to any cables, many of us believe the whole thing is wireless, said Starosielski, but the reality is far more extraordinary.

Almost all internet trafficincluding Zoom calls, movie streams, emails and social media feeds - reach us via high speed fibre optics laid on the ocean floor. These are the veins of the modern world, stretching almost 1.5m km under the sea. Speaking via WhatsApp, Starosielski explained that the data transmitting her voice would travel from her mobile phone to a nearby cell tower. "That's basically the only wireless hop in the entire system," she said.