A Volcano Erupted in Tonga We Discuss Undersea Cable Repairs

Hunga Tonga Hunga Ha Apai Volcano Eruption Credit US NWS
Hunga Tonga Hunga Ha'apai Volcano Eruption Credit US NWS

To start 2022, the Hunga Tonga-Hunga Ha’apai volcano erupted in a spectacular fashion. One of the stories coming out of the island nation of Tonga is a loss of connectivity. Undersea fiber-optic cables carry data to many islands and across oceans. We often take for granted that there are several points in the world where there are only a few cables (and some satellite) connections with the rest of the world. As one would expect, those cables sometimes need repairs.

Disclosure: At STH, we do not cover volcanic activity often, but from the images online a volcano that disrupted an area roughly the size of Poland and sent shockwaves and tsunami waves to distant parts of the Earth seems like it was a significant and devastating event. I have seen lava flows SCUBA diving in Hawaii, and hiked active volcanos in places like Guatemala, but the amount of energy being released here is not comparable and hard to comprehend. Others may not think this is a large eruption, but we are going to call it one.

A Volcano Erupted in Tonga We Discuss Undersea Cable Repairs

While one may lay multiple undersea cables for redundancy, even if those cables are many kilometers apart can still be impacted by explosions where the volcanic blast radius is well over 100km. Even though the Tonga Cable Ltd cable was situated dozens of kilometers offshore, it was still damaged as a result of the eruption.

For those that do not know, generally, the way these types of faults are fixed is that a pulse is sent from the end of the cable and is timed. Operators can use the time until some of the pulse energy is returned to get a fairly accurate estimate of the distance between the terminal (usually on land) and the cable breakpoint in the ocean. This is conceptually similar to some of the features we have been using on the Fluke Networks Versiv 2 units that we have been using, just scaled (WAY) up. Different gear is used for the undersea cables as one would imagine.

Fluke FiberInspector Pro FI 3000 Showing Up On Versiv 2
Fluke FiberInspector Pro FI 3000 Showing Up On Versiv 2

A ship is then sent to the impacted area. That ship then uses the pulse timing estimate to locate the undersea cable and retrieve the cut cable or both ends of the cable. Undersea cables have many layers of shielding to prevent not just saltwater and marine growth, but also anchor and other damage.

The cable is then brought aboard and usually repaired on a rocking boat in the ocean. Regular readers will note that at STH we usually just buy pre-terminated cables to not have to splice on land, let alone at sea.

Generally, this process takes quite some time. A ship needs to be dispatched, arrive at the location, locate the cable, determine the necessary repairs, and execute the repair work. That practically means that high-capacity fiber connectivity will be offline for more than a week to Tonga. Beyond the normal repair process, the repair ship will also need to get the OK to enter the space given the volcanic activity. A safety hold can push repairs back further.

If you want to learn more about how undersea cables are repaired, I watched this documentary a few months ago and certainly learned a lot:

It is not as action-packed as an Avengers movie, but it is interesting to have on in the background if you are not watching STH YouTube (shameless plug.)

Final Words

Hopefully this year we are going to get more into how the Internet works at a low level. As we have been planning that series, something we are factoring into the discussion is that many people see pervasive Internet access as a fact without thinking about how the connectivity is delivered. Stay tuned to STH for that.

More importantly, STH does not have an enormous readership in Tonga, but best wishes to those impacted with recovering. Many of our readers now take communication as a given, but this type of cable break means that there is limited connectivity to get in touch with those on the ground.


  1. Not only was the Tonga Net link damaged, so was the split off the Tonga Net had set up to serve another locale. The split requires extensive repair and may need all out replacement. The link to one of the trans-oceanic fiber cables was under repair shortly after the blast, but the first attempt failed apparently. I was waiting to hear what the next steps were going to be.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.