The Hunga Volcano eruption in January 2022 off the coast of Tonga did more than produce a spectacular explosion visible from space. It exposed a category of natural disaster that scientists have long worried about but rarely witnessed in full: the cascading, far-reaching destruction that submarine volcanoes can inflict on the seafloor, on global communications infrastructure, and on coastlines thousands of kilometers away. Submarine volcanoes exist by the thousands in every ocean, yet the vast majority remain unmonitored, raising hard questions about whether the next major eruption could catch the world even less prepared.
How Density Currents Reshaped the Seafloor
When Hunga erupted, the blast did not simply send ash and gas into the atmosphere. It triggered what volcanologists call volcaniclastic density currents, turbulent flows of volcanic debris that raced across the ocean floor at high speed. A peer-reviewed reconstruction published in Nature Communications documented how these flows caused seafloor change and cable damage extending beyond 100 km from the eruption site. The study estimated that nearly 10 km cubed of seafloor material was removed, a volume large enough to reshape underwater terrain across a wide swath of the Pacific and to carve new channels where none had been mapped before.
The consequences were not limited to geology. The same research found that seafloor communities were wiped out in mapped areas, meaning that organisms living on and within the seabed were buried or swept away. Undersea telecommunications cables, which carry more than 95 percent of intercontinental data traffic, were severed along those same corridors, leaving physical gaps that had to be bridged by emergency repairs and rerouting. For Tonga, that meant weeks of near-total communications blackout, with banking, government services, and contact with the diaspora all severely hindered. The practical takeaway is stark: a single submarine eruption can simultaneously destroy ecosystems, cut off digital connectivity for entire nations, and rearrange the physical landscape of the deep ocean in ways that take years to fully survey.
Atmospheric Waves and Distant Tsunamis
The seafloor destruction was only part of the story. The Hunga eruption also generated atmospheric disturbances that circled the globe multiple times. Research summarized by the U.S. Geological Survey documented globally observed Lamb waves, infrasound signals, and ionospheric perturbations, all produced by a single underwater blast. Lamb waves are pressure pulses that travel along the Earth’s surface at the speed of sound, and they were detected by barometric sensors on every continent, showing up as sharp, repeating spikes in air-pressure records as the wave fronts passed overhead again and again.
What makes this finding especially alarming is the mechanism it revealed. The coupling between atmospheric waves and the ocean surface can drive fast-arriving tsunamis that reach distant coastlines before traditional seismic tsunami models would predict. In the case of Hunga, some coastal areas far from Tonga recorded unexpected water-level surges that arrived ahead of schedule, driven not by the seafloor displacement itself but by the atmospheric pressure wave pushing on the ocean. This means that conventional tsunami warning systems, which rely on seismic detection and ocean buoy networks, may not provide adequate lead time for eruption-driven waves. The gap in preparedness is not theoretical: it played out in real time during the Hunga event, forcing emergency managers to interpret unfamiliar signals on the fly, and it could recur anywhere a large submarine volcano sits near populated coastlines.
Monitoring the Few While Thousands Go Unwatched
One bright spot in this otherwise sobering picture is the work being done at Axial Seamount, an active submarine volcano off the coast of Oregon. The Ocean Observatories Initiative operates a cabled network of instruments on and around Axial that produces a near-real-time, continuously updated earthquake catalog. This system demonstrates that submarine volcanoes can be instrumented and tracked via seismic precursors, giving scientists a window into building eruptions before they happen. Axial has already shown patterns of inflation and seismicity that preceded past eruptions, offering a proof of concept for early warning and for tying changes in seafloor shape to what the instruments record.
The problem is scale. Axial Seamount is one of a tiny handful of submarine volcanoes with this level of instrumentation. Scientists have noted that submarine volcanoes are found by the thousands in every ocean, and the overwhelming majority have never been surveyed in detail, let alone wired with sensors. The Tonga disaster made clear that these features pose real dangers, yet international investment in submarine volcano monitoring remains a fraction of what goes toward land-based volcanic and seismic networks. Extending Axial-style monitoring even to the most active submarine volcanic arcs in the Pacific would require significant new funding, shared standards for data, and multinational coordination, none of which has materialized at the necessary pace.
Why Current Risk Models Fall Short
A common assumption in hazard planning is that submarine eruptions are primarily a local concern, dangerous to nearby islands but unlikely to affect distant populations. The Hunga event challenged that assumption on multiple fronts. The density currents damaged infrastructure over 100 km away. The atmospheric coupling sent tsunami-like surges to coastlines across the Pacific and beyond. And the communications disruption affected not just Tonga but global data routing, since undersea cable networks have limited redundancy in certain regions and traffic had to be pushed through already congested paths. Treating submarine volcanoes as isolated, local hazards misreads the evidence and encourages underinvestment in both mapping and resilience.
A more honest framing is that we have built critical global infrastructure—cables, shipping lanes, coastal cities—on top of and around geological features we barely understand. The research teams working in the Tonga region, including New Zealand’s Niwa, which is well placed to investigate Hunga’s impact given the seismically active waters they operate in, are doing essential work to fill that gap. But their efforts also highlight how much remains unknown: vast stretches of seafloor have never been mapped at high resolution, many cable routes cross uncharted volcanic terrain, and hazard models still struggle to integrate processes like density currents and atmospheric-ocean coupling. The risk is not just that another Hunga-scale eruption will surprise us, but that it will do so in a place where our blind spots are even larger.
Building a More Realistic Preparedness Strategy
Preparing for the next major submarine eruption will require a shift in both mindset and investment. On the scientific side, the Hunga event argues for prioritizing detailed bathymetric mapping along critical infrastructure corridors, especially where cables and shipping routes intersect known volcanic arcs. It also makes the case for expanding permanent seafloor observatories beyond showcase sites like Axial, at least to a network of representative volcanoes that can serve as analogs for broader regions. Combining such observatories with satellite remote sensing, ship-based surveys, and rapid post-eruption mapping campaigns would create a feedback loop, improving models each time a submarine volcano shows signs of unrest.
On the policy and infrastructure side, governments and industry face hard choices. Cable operators can reroute some future lines away from the most hazardous slopes, but many chokepoints are unavoidable, making redundancy and rapid repair capacity crucial. Coastal communities, meanwhile, need tsunami guidance that explicitly accounts for atmospheric-triggered waves, not just earthquake-driven ones, and warning centers must be trained to interpret the unusual signals that eruptions like Hunga produce. None of these steps will eliminate the danger posed by submarine volcanoes. They can, however, narrow the gap between the scale of the threat and the thin layer of monitoring and planning that currently stands between an underwater blast and its far-flung consequences.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
