Tonga volcano ruined 124 miles of underwater telecom cables

However, many of Earth's volcanoes lie beneath the ocean's surface, and despite their prevalence, our understanding of explosive underwater eruptions remains limited. This reality makes it challenging to assess associated risks accurately.

To bridge this knowledge gap, Michael Clare and a team of researchers analyzed observations of volcaniclastic flows triggered during the 2022 eruption of Hunga Tonga–Hunga Ha'apai in Tonga. 

They found that this event destroyed nearly 200 kilometers (124 miles) of vital subsea telecommunications cables.

To put the scale of this catastrophe into perspective, consider traveling in a car at a constant speed of 100 kilometers per hour (approximately 62 miles per hour). If you were to maintain that speed for two hours, you would cover a distance of 200 kilometers.

By combining data from cable breakages, repeated bathymetric surveys, eruption observations, and rock core sampling, Clare and his team uncovered the true nature of the disaster. 

They found that the ejected rock and ash from the Hunga eruption collapsed directly into the ocean, forming an exceptionally fast-moving and highly destructive underwater debris flow.

The shocking findings indicate that this submarine density current traveled more than 100 kilometers across the seafloor, reaching speeds of up to 122 kilometers (75 miles) per hour. 

100-meter-deep scours

Moreover, the force of these volcanoclastic currents significantly altered the underwater landscape around the Hunga volcano, creating scours and channels over 100 meters deep in the surrounding seabed.

Remarkably, similar landforms have been observed around many other submerged volcanoes, suggesting that powerful underwater flows like those witnessed during the Hunga eruption may have occurred at various sites worldwide during large eruptions.

The study's implications extend far beyond a single volcanic event. It underscores the need for enhanced monitoring and assessment of undersea volcanic activity, particularly in regions where critical telecommunications infrastructure is at risk. 

As our reliance on undersea cables for global communication continues to grow, understanding and mitigating these newfound threats becomes paramount.

The complete study was published in Science on September 7 and can be found here.

Study abstract:

Volcanic eruptions on land create hot and fast pyroclastic density currents, triggering tsunamis or surges that travel over water where they reach the ocean. However, no field study has documented what happens when large volumes of erupted volcanic material are instead delivered directly into the ocean. We show how the rapid emplacement of large volumes of erupted material onto steep submerged slopes triggered extremely fast (122 kilometers per hour) and long-runout (>100 kilometers) seafloor currents. These density currents were faster than those triggered by earthquakes, floods, or storms, and they broke seafloor cables, cutting off a nation from the rest of the world. The deep scours excavated by these currents are similar to those around many submerged volcanoes, providing evidence of large eruptions at other sites worldwide.