* Volcanic eruption unleashed tsunamis, severed connectivity
* Specialist repair ship could take days to get to fault site
* Submarine cables carry over 99% of international data traffic
By Praveen Menon and Tom Westbrook
WELLINGTON/SYDNEY, Jan 18 (Reuters) - The South Pacific archipelago of Tonga could spend days, or even weeks, cut off from the rest of world because of difficulties in repairing its sole undersea communications cable, which an operator said was ruptured during a massive volcanic eruption.
The challenge underlines the vulnerability of undersea fibre-optic cables, which have become the backbone of global communications, thanks to a capacity to carry data that is about 200 times that of satellites.
Saturday's explosion of the Hunga Tonga-Hunga Ha'apai volcano sent tsunami waves across the Pacific Ocean so that connectivity was lost on the line, operated by Tonga Cable Ltd, in waters about 37 kilometres (23 miles) offshore.
But the repair of Tonga's critical 827-km (514-mile) fibre-optic link to Fiji depends on the arrival of a specialised ship now days away in Port Moresby, the capital of Papua New Guinea.
"Typically, all things going well, it would take around two weeks," said Craige Sloots, marketing and sales director at Southern Cross Cable Network, which connects to the Tonga cable at Fiji.
That covers the eight or nine days the Reliance, the specialist cable repair ship in Port Moresby, will take to reach the affected area, while the crew also needs safety clearance for the repairs, he added.
"Its ability to repair would also be dependent, as you would expect, on any volcanic activity," Sloots, who is based in Sydney, told Reuters.
"Fault-finding by Fintel and Tonga Cable Ltd on Sunday afternoon seems to confirm a likely cable break," added Sloots, referring to Fiji's telecoms provider.
The Reliance, owned by U.S. firm SubCom, a builder of underwater cable networks that is the repair contractor for more than 50,000 km (31,070 miles) of cable in the South Pacific, has completed five-yearly maintenance in Singapore.
It is in Port Moresby en route to its base in New Caledonia.
SubCom, owned by U.S. private equity firm Cerberus Capital Management, said it was working with Tonga Cable Ltd to mobilise the Reliance for the cable repairs, while it evaluated crew and ship safety.
Fixing a break in a fibre-optic cable on land is easy for an experienced technician, but repairing a cut in one on a seabed is far more complicated.
Cable operators must first locate the fault by seeing how far a pulse of light travels down the cable before it bounces back at the break.
Then a repair ship heads to the site of the break, where it sends down a submersible or deep water hook to grab the cable and pull it up to make the repair.
GLOBAL SUBSEA NETWORK
More than 99% of global international data traffic is still carried on a network of about 280 submarine cables stretching more than a million kilometres (621,000 miles).
In 2019, Tonga spent more than a week cut adrift from the web, when the undersea cable was damaged, reportedly by a ship's anchor. After that outage, it signed a 15-year deal for satellite connectivity.
But prohibitive costs limit the use of satellites across the archipelago for most people apart from government, officials and some businesses.
The use of satellite phones has also been affected by the ash still blanketing the country after the eruption.
Australia and New Zealand Banking Group Pacific spokeswoman Victoria Kanevsky said Tonga country head David Dudley could only dial out on his satellite phone, and get signals only when he was down at the waterfront in the capital, Nuku'alofa.
Digicel, an international mobile network provider, said it had set up an interim system on the main island of Tongatapu using the University of the South Pacific's satellite dish, which could allow limited 2G coverage.
Worried relatives overseas still face an agonising wait for news.
"We just wait and pray and hope that communications come back soon because we don't know anything," said Pauline Lavulo, whose husband Aqulia is a pastor to the Tongan community in Sydney.
"Every Tongan ... wherever we are in the globe, we still have family back home."
(Reporting by Praveen Menon and Tom Westbrook; Writing by Jane Wardell; Editing by Clarence Fernandez)
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