On January 15, 2021, Hunga Tonga–Hunga Ha’apai – a volcano located 65 kilometres north of Tongatapu, Tonga’s main island – spectacularly erupted, killing at least three people and sending an ash plume high into the atmosphere.
The blast devastated nearby islands, covering them in ash and triggering tsunamis that destroyed or damaged 600 Tongan buildings and reached as far as Peru, where a two-metre wave killed two people.
It is believed to be the largest eruption of the twenty-first century and the largest recorded since Mount Pinatubo erupted in the Philippines in 1991.
The blast ruptured the 872-kilometre-long undersea fibre-optic cable linking Tonga to Fiji, cutting communications and plunging the island nation into radio silence.
The cable, first laid in 2013 and financed by World Bank Group and the Asian Development Bank, was Tonga’s sole source of fast and reliable internet.
The lack of internet left authorities unable to ascertain the extent of damage across the archipelago and left friends and family in Australia and elsewhere unable to check in with loved ones in Tonga.
Reconnecting Tonga to the world
The country had no internet at all for five days following the eruption until a satellite connection was established, which provided limited coverage to 85 per cent of the population. However, according to Reuters, the use of satellite phones was impaired by the volcanic ash blanketing the country, meaning people could dial out but were unable to receive calls.
On January 20, CS Reliance, a repair ship owned by undersea cable laying company SubCom, left Port Moresby headed for Tonga.
“There are very few vessels that are equipped to lay and repair undersea cables,” Amanda Watson, a researcher at the Australian National University’s Department of Pacific Affairs, told The New York Times.
To repair damaged cables, the repair team uses light pulses to locate the breakage. Next, deep-sea hooks known as grapnels retrieve the severed ends of the cable, which are then repaired on deck. “A technician splices the glass fibres and uses glue to attach the new section of the cable,” Reuters reports. “This fibre optic splicing can take up to 16 hours and is the most crucial aspect of the repair work.”
Once spliced, the cable is wrapped in protective layers. The repaired cable, around the width of a garden hose, is then gently lowered to the seabed. In some cases, a sea plough is used to bury the cable.
In Tonga, the repair process was made more complex by the threat of further volcanic activity and the effects of the COVID-19 pandemic, which has disrupted global supply chains.
Internet was finally restored to Tonga on February 22, five weeks after the eruption.
The global submarine cable network
The highly connected modern world relies on undersea cables like the one linking Tonga to Fiji, with more than 95 per cent of global data transfer passing through 885,000 kilometres of fibre-optic cables that criss-cross the world’s oceans.
“These cables cluster in narrow corridors and pass between so-called critical ‘choke points’ which leave them vulnerable to a number of natural hazards including volcanic eruptions, underwater landslides, earthquakes and tsunamis,” writes Dale Dominey-Howes, Professor of Hazards and Disaster Risk Sciences at the University of Sydney, in The Conversation.
Ship anchors and fishing trawlers are also responsible for damage to cables. “Breakage or interruption to this critical infrastructure can have catastrophic local, regional and even global consequences,” he writes.
Tonga’s disconnection from the world following the Hunga Tonga eruption highlights the weaknesses of the global undersea cable network.
Broken cables can take weeks – sometimes months – to repair, resulting in extended outages. “At times of crisis, such outages make it much harder for governments, emergency services and charities to engage in recovery efforts,” Dominey-Howes explains.
Australia, connected to the network via points in Sydney and Perth, is vulnerable to communications outages in the event of damage to submarine cables.
Dominey-Howes argues that more research is needed to quantify and evaluate the risk to submarine cables in particular places on the ocean floors and to different natural hazards.
“At the same time,” he writes, “governments and the telecommunication companies should find ways to diversify the way we communicate, such as by using more satellite-based systems and other technologies.”