The eruption of the Hunga Tonga–Hunga Ha’apai submarine volcano on January 15, 2022, triggered one of the most unusual tsunamis in recorded history. Unlike most tsunamis, which are caused by earthquakes, this one was driven in part by atmospheric pressure waves that raced around the globe, pushing sea levels up thousands of kilometers from the eruption site and catching coastal communities and warning systems off guard. The event killed several people in Tonga and as far away as Peru, severed Tonga’s only international communications link, and injected an unprecedented volume of water vapor into the stratosphere, with climate effects researchers are still tracking years later.
What Happened Beneath the Surface
Hunga Tonga–Hunga Ha’apai is a submarine volcano in the South Pacific, located about 65 kilometers north of Tonga’s main island of Tongatapu. The volcano had been rumbling for weeks before the climactic eruption on January 15, but nothing hinted at the scale of what came next. Seafloor mapping conducted before and after the event revealed that the center of the volcano collapsed by more than a kilometer, displacing roughly 9 cubic kilometers of material in a single catastrophic episode.1Nature Geoscience. Sudden collapse of submarine volcano drives extreme hazards That sudden collapse is what drove the extreme hazards that followed: the massive tsunami, the eruption column that shot into the stratosphere, and the severing of submarine telecommunications cables on the ocean floor.
The explosion itself was staggering. Atmospheric pressure sensors and seismic stations worldwide recorded signals comparable in magnitude to those produced by the 1883 eruption of Krakatoa, an event that holds a near-mythic place in the history of natural disasters.2PubMed. Atmospheric waves and global seismoacoustic observations of the January 2022 Hunga eruption, Tonga A surface-guided pressure wave known as a Lamb wave was observed circling Earth four times in one direction and three more times off the opposite side, persisting for six days.3Pure and Applied Geophysics. TIMING Analysis of the Multiple Passages of the Pressure Wave Generated by the 2022 Hunga Tonga-Hunga Ha’apai and Comparison with the 1883 Krakatoa Pressure Wave The eruption also produced long-range audible sound detectable over 10,000 kilometers away and infrasound that registered on monitoring stations across every continent.
How Atmospheric Waves Spread the Tsunami Worldwide
Most tsunamis travel through the ocean as gravity waves, pushed along by the displacement of water from an earthquake or landslide. The Tonga tsunami did that too, but what made it exceptional was a second mechanism running in parallel. The atmospheric Lamb wave, a fast-moving pressure disturbance that hugged Earth’s surface, pressed down on the ocean as it traveled, generating sea-level rises far from the volcano at speeds much faster than any conventional ocean wave could travel.
Simulations confirmed that this Lamb wave drove the leading rise in sea height at distant coastlines, arriving well before the slower ocean-borne tsunami would have.4PubMed. Global fast-traveling tsunamis driven by atmospheric Lamb waves on the 2022 Tonga eruption The coupling between the atmosphere and the ocean surface was most efficient over deep water. When the pressure wave crossed shallower continental shelves, the air-sea coupling weakened and the wave amplitude shrank. Japanese data showed the atmosphere-driven tsunami was initially generated at a speed of about 0.31 kilometers per second, matching the speed of the Lamb wave, but split and slowed when it passed over the continental slope, transitioning into a conventional ocean gravity wave.5Geophysical Research Letters. Tsunami Triggered by the Lamb Wave From the 2022 Tonga Volcanic Eruption and Transition in the Offshore Japan Region The scattering of these waves off underwater features like ridges and seamounts in the Pacific produced long-lasting secondary tsunamis that continued arriving at coastlines for hours.
This mechanism matters because it broke the assumptions built into existing tsunami warning systems. A conventional earthquake tsunami radiates outward from a point source in the ocean. Forecasters can calculate when it will reach each coastline based on ocean depth and distance. But the Lamb-wave-driven tsunami traveled through the atmosphere at roughly the speed of sound, arriving at distant shores hours earlier than models predicted for an ocean-only wave.6Geoscience Letters. Atmospheric Lamb wave inversion from the 2022 Hunga Tonga–Hunga Ha’apai eruption for tsunami prediction For people on the ground, this meant sea-level anomalies appeared with little or no advance notice.
Devastation Close to Home
For the people of Tonga, the tsunami was immediate and overwhelming. Modeling of the wave field around Tongatapu showed that the southern coast bore the worst of it, with water levels reaching roughly 15 meters along stretches of shoreline close to the island.7Scientific Reports. The near-field tsunami generated by the 15 January 2022 eruption of the Hunga Tonga-Hunga Ha’apai volcano and its impact on Tongatapu, Tonga The northern coast fared better in most areas, averaging about 1.5 meters close to shore, in large part because a broad zone of shallow coral reef acts as a natural barrier that dissipates wave energy before it reaches land. But even on the north side, localized spots on the western coast reported water levels near 15 meters.
The eruption also destroyed Tonga’s connection to the outside world. Two submarine telecommunications cables connect Tongatapu to the rest of the kingdom and to the global internet via Fiji and Australia. Both were severed on the day of the eruption, the domestic cable breaking first and the international cable following about an hour later. When backup satellite links finally kicked in five days later, data capacity was less than one percent of normal levels.8PubMed Central. Volcanic eruptions and the global subsea telecommunications network For days, the outside world had almost no information about conditions on the ground. Aid coordination was hampered, families abroad had no way to reach relatives, and the Tongan government struggled to communicate even within its own island chain. The communication blackout was itself a humanitarian crisis layered on top of the physical destruction.
A Tsunami Felt Across the Pacific and Beyond
The combination of ocean-borne and atmosphere-driven waves meant the Tonga tsunami registered on tide gauges across the Pacific, the Caribbean, the Mediterranean, and even the Atlantic. But its most consequential far-field impact happened in Peru, more than 10,000 kilometers from the volcano.
About 15 hours after the eruption, tsunami waves arrived at the port of La Pampilla in Callao, Peru. A moored oil tanker’s lines failed under the stress, releasing over 11,000 barrels of crude oil into the sea.9Natural Hazards and Earth System Sciences. Volcano tsunamis and their effects on moored vessel safety: the 2022 Tonga event Researchers who later analyzed the event found that the peak energy in the wave spectrum off Peru corresponded to an unusually long wave period of about 120 minutes. Waves with that kind of period can produce large, slow shifts in water level inside port basins, creating forces on moored vessels that exceed the breaking strength of standard mooring lines. The timing of these long-period arrivals matched the moment the tanker broke free. The resulting oil spill contaminated beaches and marine habitats along the Peruvian coast and became one of Peru’s worst environmental disasters in recent years, all triggered by a volcano thousands of kilometers away.
The Peru event highlighted a hazard that port engineers and maritime authorities had not fully reckoned with. Tsunami warnings for coastal populations typically focus on wave run-up height at the shoreline. But the Tonga event showed that even modest wave heights can generate dangerous currents and water-level oscillations inside harbors, with consequences for industrial infrastructure.
An Eruption That Reshaped the Stratosphere
Because Hunga Tonga–Hunga Ha’apai is a submarine volcano, its eruption column ripped through a vast volume of seawater on its way into the atmosphere. The result was a plume that carried an extraordinary quantity of water vapor to extreme altitudes. Satellite-based stereo methods showed the eruption plume’s overshooting tops reaching 50 to 55 kilometers above the surface, the highest volcanic plume ever measured in the satellite era.10Geophysical Research Letters. Stereo Plume Height and Motion Retrievals for the Record‐Setting Hunga Tonga‐Hunga Ha’apai Eruption of 15 January 2022
What the plume carried into the stratosphere was equally remarkable. Measurements showed the eruption injected at least 50 teragrams of water vapor directly into the stratosphere, raising the global amount of stratospheric water vapor by more than five percent.11PubMed. Water vapor injection into the stratosphere by Hunga Tonga-Hunga Ha’apai Later estimates pushed the total even higher, to around 150 to 160 teragrams.12PubMed Central. Impact of water vapor on stratospheric temperature after the 2022 Hunga Tonga eruption: direct radiative cooling versus indirect warming by facilitating large particle formation This was, by a wide margin, the largest injection of water vapor into the stratosphere ever observed by instruments.13PubMed Central. Impact of the Hunga Tonga volcanic eruption on stratospheric composition
This matters because volcanic eruptions normally cool the planet. They do so by lofting sulfur dioxide into the stratosphere, where it forms tiny sulfate particles that reflect sunlight. The 1991 eruption of Mount Pinatubo, for instance, cooled global temperatures by about half a degree Celsius for a year or two. Hunga Tonga produced relatively little sulfur dioxide but dumped an enormous amount of water. Water vapor is a potent greenhouse gas, which raised the possibility that this eruption could produce a small net warming effect rather than the cooling typically associated with major eruptions. Whether that warming materialized in global surface temperatures has been a subject of active research.
The Competing Temperature Effects in the Stratosphere
Inside the stratosphere itself, the water vapor set off a complicated chain of effects that played out over different altitudes. In the mid-stratosphere, the extra water vapor acted as a coolant, absorbing and re-emitting infrared radiation in a way that lowered temperatures by up to 4 degrees Celsius. That cooling signal persisted for over a year.14Geophysical Research Letters. Analysis and Impact of the Hunga Tonga‐Hunga Ha’apai Stratospheric Water Vapor Plume
Meanwhile, the abundant water vapor helped sulfate particles grow much larger than they normally would. Condensation and nucleation processes driven by the water accounted for about 90 percent of the observed particle growth, roughly tripling their radius. These bigger particles eventually settled downward under gravity into the lower stratosphere, where their increased ability to absorb and scatter radiation produced a warming effect of 1 to 2 degrees Celsius, with about half of that warming attributed directly to the large particles that formed higher up and drifted down.15PubMed Central. Impact of water vapor on stratospheric temperature after the 2022 Hunga Tonga eruption: direct radiative cooling versus indirect warming by facilitating large particle formation So the eruption simultaneously cooled the upper stratosphere and warmed the lower stratosphere, a vertical split in temperature response that is unusual for a volcanic event and is still being studied for its longer-term implications on ozone chemistry and atmospheric circulation.
Ripples in the Ionosphere
The eruption’s effects were not confined to the ocean and the lower atmosphere. The explosion sent energy all the way to the ionosphere, the electrically charged layer of the upper atmosphere that sits roughly 80 to 600 kilometers above Earth’s surface. Using data from over 4,700 satellite navigation receivers worldwide, researchers tracked traveling ionospheric disturbances radiating outward from the eruption site.16Geophysical Research Letters. Global Propagation of Ionospheric Disturbances Associated With the 2022 Tonga Volcanic Eruption Two distinct large-scale disturbances appeared first, initially traveling at speeds close to one kilometer per second before slowing substantially. Smaller-scale disturbances followed for at least six hours.
Japanese researchers detected the same disturbances using their own dense receiver network, confirming two different types of ionospheric waves with distinct characteristics.17Earth, Planets and Space. Ionospheric disturbances observed over Japan following the eruption of Hunga Tonga-Hunga Ha’apai on 15 January 2022 Analysis in the Australian region found a close resemblance between the velocity profile of near-field ionospheric disturbances and the tsunami itself, suggesting direct coupling between the ocean waves and the atmospheric response. In the far field, ionospheric disturbances propagated at about 300 meters per second and continued circling the globe for at least three days, possibly up to six days after the eruption.18Geophysical Research Letters. On the Propagation of Traveling Ionospheric Disturbances From the Hunga Tonga‐Hunga Ha’apai Volcano Eruption and Their Possible Connection With Tsunami Waves
These findings are more than academic curiosities. GPS and other satellite navigation systems depend on signals passing through the ionosphere, and large disturbances can degrade positioning accuracy. The Tonga eruption provided the first clear demonstration that a single volcanic event can alter the ionospheric state on a truly global scale, a finding with practical implications for navigation system reliability during major geological events.
Why Warning Systems Were Caught Off Guard
The global tsunami warning infrastructure was designed primarily for earthquake-generated tsunamis. Seismic networks detect an undersea earthquake within minutes, models estimate wave heights and travel times based on the quake’s location and magnitude, and alerts go out to coastal communities in the projected path. The system works well for its designed purpose. It was not designed for what Hunga Tonga did.
Volcanic tsunamis differ from seismic tsunamis in a fundamental way: there are many different mechanisms by which a volcano can generate waves. Caldera collapse, pyroclastic flows entering the sea, submarine landslides, and atmospheric pressure coupling can all produce tsunamis, sometimes simultaneously during a single eruption.19Pure and Applied Geophysics. A Review of Tsunamis Generated by Volcanoes (TGV) Source Mechanism, Modelling, Monitoring and Warning Systems Each mechanism produces waves with different speeds, periods, and propagation patterns. The atmosphere-driven component of the Tonga tsunami arrived at some coastlines before any ocean-based warning could have been issued, because the waves literally outran the models. In the Caribbean and Mediterranean, where volcanic tsunamis from the South Pacific are essentially unheard of, the sea-level anomalies were completely unexpected.
The 2018 eruption and flank collapse of Anak Krakatau in Indonesia, which killed over 400 people, had already exposed similar gaps. Both events have pushed scientists and warning agencies to think harder about how to detect and communicate volcanic tsunami hazards in real time. One promising avenue involves using barometric pressure data, which is already collected at thousands of weather stations worldwide, to detect Lamb waves and estimate their tsunami-generating potential before the waves reach distant coastlines.
What Happened to the Coral Reefs
The eruption blanketed nearby waters with volcanic ash, raising concerns about the health of Tonga’s coral reef ecosystems. Volcanic ash deposition can damage coral in the short term by physically burying organisms, blocking light, and altering water chemistry. Satellite monitoring of reefs in the eruption’s fallout zone confirmed these kinds of negative effects in the immediate aftermath.20Environmental Research Letters. Satellite monitoring of coral reef responses to the 2022 volcanic ash deposition of the Hunga Tonga–Hunga Ha’apai
The longer picture is more nuanced. Volcanic eruptions have occurred near coral reef habitats throughout geological history, and the relationship is not purely destructive. Over longer timescales, volcanic substrates can provide new surfaces for coral colonization, and nutrient inputs from volcanic material can sometimes support reef growth. Whether Tonga’s reefs recover quickly or suffer lasting damage depends on factors like the thickness and chemistry of the ash layer, the health of the reefs before the eruption, and whether additional stressors such as marine heat waves compound the damage. For reef systems already weakened by bleaching and ocean acidification, the added burden of volcanic ash deposition may tip the balance toward long-term degradation.
Hydroacoustic Signals and What They Revealed
The eruption also sent powerful pulses of sound through the ocean itself. Researchers analyzed recordings from freely drifting ocean-floor sensors and from fixed hydrophones in the global monitoring network. They detected a 30-minute-long acoustic signal, known as a T wave, propagating horizontally through the ocean with energy concentrated in the 2.5 to 10 hertz range.21Journal of Geophysical Research: Solid Earth. Hydroacoustic Observations of the 15 January 2022 Hunga Tonga‐Hunga Ha’apai Eruption: The Role of Bathymetry Along the Path Separate analysis of the International Monitoring System’s hydroacoustic stations showed a broader 40-minute window of underwater acoustic activity, with the main eruption simultaneously generating low-frequency seismic body waves, large atmospheric infrasound waves, and the tsunami.22Seismological Research Letters. The Hunga Tonga–Hunga Ha’apai Eruption of 15 January 2022: Observations on the International Monitoring System (IMS) Hydroacoustic Stations and Synergy with Seismic and Infrasound Sensors
These recordings are scientifically valuable because the same monitoring network was originally built to detect clandestine nuclear tests. The fact that a single volcanic event registered on seismic, hydroacoustic, infrasound, and barometric networks simultaneously gave researchers an unusual opportunity to study how energy from a single source partitions across solid earth, ocean, and atmosphere. The data have already informed better models of how submarine eruptions generate hazards, and they serve as a benchmark for calibrating detection systems against a known event of extreme magnitude.
Indigenous Knowledge and Volcano-Tsunami Preparedness
In parts of the Pacific and Indian Ocean that live with recurring volcanic and seismic hazards, communities have long relied on observational knowledge passed down across generations to recognize the signs of incoming tsunamis. In the Mentawai Islands of Indonesia, for instance, traditional leaders teach younger generations to watch for sudden changes in the sea, such as water rapidly receding to expose the seabed or the appearance of abnormally high waves, and to treat these as immediate evacuation signals. This knowledge is practiced in everyday life as part of ongoing preparedness, not just recited in emergencies.
The Tonga event underscored both the value and the limits of this kind of knowledge. For people living close to the volcano, established awareness of tsunami risk likely saved lives. Several communities on low-lying islands evacuated to higher ground quickly after feeling the eruption’s shockwave, relying on a basic principle that many Pacific cultures share: if the ground shakes or the sea behaves strangely near a volcano, move uphill immediately. But the atmosphere-driven component of the tsunami, the portion that reached distant shores without any preceding earthquake, fell outside the experiential framework of communities thousands of kilometers away. No traditional knowledge system includes a template for a wave arriving from the air. Bridging that gap between local knowledge and modern atmospheric science is one of the unresolved challenges the Tonga event left behind.