The Tonga eruption explained, from tsunami warnings to sonic booms
The volcanic plume generated record amounts of lightning before producing a blast heard thousands of miles away. Here’s what geologists say drove the event—and what may happen next.
Then, early in the morning on January 15, the volcano produced a colossal explosion. The atmosphere was blasted out of the way as a shockwave emanated from the island, radiating outward at close to the speed of sound. The sonic boom was heard in parts of New Zealand more than 1,300 miles away, with the shockwave eventually traveling halfway around the world—as far as the United Kingdom, which is located a staggering 10,000 miles distant.
To everyone’s horror, a tsunami quickly followed. It hit Tongatapu, the kingdom’s main island and home to the capital Nuku’alofa, just a few dozen miles to the south of the volcano. Communications were knocked out as the streets began to flood and people fled for their lives. Tsunami waves, albeit smaller ones, rushed across the vast ocean to parts of the Pacific Northwest, causing surges in Alaska, Oregon, Washington State, and British Columbia. Stations in California, Mexico, and parts of South America also registered minor tsunami waves.
Recent research on the geologic history of the volcano suggests that this powerful paroxysm is, on human timescales, a relatively rare event: Such an explosion is thought to occur roughly once every thousand years. The hope is that the worst of the eruption is over. But even if that turns out to be the case, the damage has already been done.
For Tonga, this is a potentially devastating event, and it’s horrifying to watch.
Scientists and a rattled public are eager to know what caused such a powerful eruption, and what may happen next. But information has been slow to emerge partly because the volcano is somewhat remote and difficult to observe up close.
There are far more questions than answers at this point. But here’s what scientists do know about the tectonic and geologic drivers involved, and what they might mean for the volcano’s future.
A volcanic powerhouse in the Pacific
Hunga Tonga-Hunga Ha’apai is located in region of the South Pacific that’s jam-packed with volcanoes—some above the waves, some far below—that have a penchant for violent eruptions. Past events have unleashed city-size rafts of pumice or seen volcanoes blowing themselves apart only to build new islands immediately afterward.
This profusion of volcanoes exists because of the Pacific plate’s continuous dive beneath the Australian tectonic plate. As the slab descends into the superhot rocks of the mantle, the water inside gets baked out and rises into the mantle above. Adding water to these rocks causes them to more readily melt. This creates a lot of magma that tends to be sticky and filled with gas—a potent recipe for explosive eruptions.
Hunga Tonga-Hunga Ha’apai is no exception to this rule. The bits of land sit above a volcano more than 12 miles wide featuring a cauldron-like pit about three miles across, hidden from view by the sea. It’s been seen erupting with vim and vigor as far back as 1912, sometimes popping above the waves before being eroded away. The eruption of 2014-15 created a stable island that was soon home to colorful plants and barn owls.
When Hunga Tonga-Hunga Ha’apai started erupting again on December 19, 2021, it produced a series of blasts and an ash column 10 miles high, but it was doing nothing out of the ordinary for a submarine volcano. For the next few weeks, enough fresh lava erupted to expand the island by nearly 50 percent. And as the new year dawned, the volcano appeared to be calming down.
Then, in the last couple of days, things took a turn for the dramatic.
The volcano’s menacing maelstrom
As the volcano’s explosivity began to intensify, the amount of lightning emerging from its ashy plume began to eclipse not only that seen during this eruption, but during any eruption ever recorded.
Volcanoes can produce lightning because ash particles in their plumes bump into each other or into bits of ice in the atmosphere, which generates an electrical charge. Positive charges get segregated from negative ones, sparking a flash of lightning. (Learn more about how volcanoes can trigger lightning.)
From the outset, the Tonga eruption’s lightning was detected by Vaisala’s GLD360 network, which uses a global distribution of radio receivers that can “hear” the lightning as intense bursts of radio waves. During the first two weeks, the system recorded sometimes a few hundred or a few thousand flashes per day—nothing unusual. “It was clearing its throat, I guess,” says Vagasky.
But by late Friday into early Saturday, the volcano was producing tens of thousands of discharges. At one point, this Tongan volcano managed 200,000 discharges in a single hour. By comparison, the 2018 eruption of Indonesia’s Anak Krakatau had 340,000 discharges over a week or so.
I couldn’t believe the numbers I was seeing. You don’t usually see that with a volcano. This is something else. There was nowhere else that was that electric on the planet last night.
It may have looked spectacular from afar, but up close it would have seemed apocalyptic, a constant blaze of light soundtracked by endless thunder and volcanic bellows. Most of the lightning wasn’t isolated to the plume but also hit the ground and the ocean. “This was extremely dangerous for anybody that’s sitting on any of the other Tongan islands, because you’ve got all this lightning coming down around you.
So why has this eruption produced what is likely to be a record-breaking number of discharges?
The presence of water always ups the odds of lightning, says Kathleen McKee, a volcano acoustic researcher at the Los Alamos National Lab in New Mexico. When magma mingles with a shallow body of water, the trapped water is aggressively heated and vaporized, blasting that magma into millions of tiny pieces. The more plentiful and the finer the particles you have, the more lightning you generate.
The heat of the eruption also readily transports water vapor into the colder, higher reaches of the atmosphere, where it becomes ice. That provides plenty of additional particles for the ash to collide with and generate electricity.
But the reasons this eruption produced quite so much lightning are impossible to determine at present. “Unfortunately, the volcano is quite remote and there [are] few constraints on the atmospheric profiles in the vicinity of the plume.
The Hephaestion hammer falls
The astounding amount of lightning wasn’t the only prelude to the volcano’s cataclysmic blast. By Saturday morning, satellite imagery had revealed the island was no longer building itself: The middle of the volcanic isle had vanished, likely thanks to the uptick in explosivity.
When it eventually unleashed a giant explosion, the shockwave ricocheted across the globe at breakneck speeds. It was immediately followed by a tsunami that slammed into several islands in the Tongan archipelago before racing across the Pacific.
The blast involved a mind-boggling amount of energy. But there isn’t enough data right now to ascertain the precise cause of the tsunami.
These events require displacing a lot of water, which can happen through underwater explosions, through a collapse event—when lots of rock suddenly falls off the volcano into the sea—or a combination of these and other factors.
With the ash column obscuring the volcano, and much of the volcano submerged underwater, scientists will need time to gather more indirect data before drawing any conclusions. Clues could come from the types of acoustic waves the blast generated or perhaps the redistribution of mass around the volcano.
The jury is still out, but the fact that such an intense explosion and potent tsunami came out of this single, relatively small volcanic isle speaks to the incredible power of this eruption. And although not the cause of the main tsunami, the shockwave itself triggered another big wave: The rapidly moving air impacting the ocean was powerful enough to force water to move out of the way, a phenomenon called a meteotsunami.
Clues about why this event was so intense can be found in the volcano’s chemistry, which changes as the magmatic fuel within evolves over time.
This volcano, like many others, must refill its magma reservoir after a major eruption. The last of those in the region happened back in the year 1100; ever since, molten rock has been accumulating at depth. As it becomes mostly full, small amounts of magma leak out of the volcano, which is likely behind the eruptions recorded since 2009.
However, once recharged, the large amount of magma crystallizing starts to drive gas pressures up, too quickly for it to be released by small eruptions. Something’s got to give, and when that vast supply of magma finds an opening, it violently depressurizes and much of the molten reservoir is evacuated in one big blast.
A foggy future in Tonga
The Tongan archipelago may owe its very existence to the infernal forces that constructed its islands in the first place, but it’s clear the cost of living on them can be steep. Only 100,000 people live in the kingdom, with about a quarter residing in the capital, and they are now besieged by ashfall and tsunami waves.
The biggest unknown right now that really matters is we don’t know how the people in Tonga are. This eruption, Mitchell adds, could potentially be incredibly devastating to the country.
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Tonga’s volcanic eruption triggered a staggering 2,600 lightning flashes a minute
The enormous eruption generated hundreds of times more power than an atomic bomb—and the most extreme lightning ever recorded. How did it happen?
PHOTOGRAPH BY RANDY OLSON, NAT GEO IMAGE COLLECTION
After weeks of grumbling and spitting ash, the underwater caldera near the tiny Kingdom of Tonga reached an unexpected fever pitch on January 15, 2022. In the world’s largest volcanic eruption in more than a hundred years, the Hunga volcano belched 2.3 cubic miles of molten rock and vaporized 146 teragrams of water—enough to fill 58,000 Olympic swimming pools.
The resultant plume—a mushroom cloud of volcanic gases, magma bits called tephra, and vaporized seawater—towered 36 miles high, about halfway to space.
But what really rattled volcanologists? The initial readings showed an enormous ring of lightning expanding from the eruption’s epicenter at around 180 miles per hour. (Read how the Tonga eruption destroyed an island—and created many mysteries.)
Volcanic lightning is well documented—even Pliny the Younger mentions it in his account of the eruption of Mount Vesuvius in 79 A.D.
But, I don’t think any of us really expected to ever see a 280-kilometer-diameter donut of electrical discharges.
The eruption created the most intense lightning event in the scientific record, generating a staggering 2,600 lightning strikes per minute at its peak. That’s more than double the previous titleholder—a 1999 thunderstorm in the U.S. Southeast, when NASA counted 993 flashes a minute.
And after combining data from several remote-monitoring systems, she and her team believe they’ve reconstructed how it happened: Plume particles surfing a volcanic “gravity wave” created the perfect storm for record-setting lightning.
Eavesdropping on plasma
Since very few of the world’s active volcanoes are directly monitored, volcanologists piggyback on other monitoring networks to get insight into eruptions in progress.
Fortunately, a U.S. weather satellite accidentally captured a bird’s-eye view of the Hunga eruption, allowing them to map the plume’s development. But the satellite’s onboard lightning-detection system only spotted occasional flashes. For Van Eaton to map the lightning ring, she’d need to tune in to the radio. (Read more details about how the Tonga eruption occurred.)
Thunder isn’t the only sound lightning makes. When lightning streaks across the sky, sometimes you see it pulse—you see it flicker a couple times.
That pulse is electrons moving through a plasma channel, creating a powerful electromagnetic signal that manifests as both visible light—the bright flash—and radio waves outside the range of human hearing that can be detected thousands of miles away.
Three ground-based, lightning-detection networks picked up on radio waves from the Hunga eruption, and by meticulously combining their data, Van Eaton and her team were able to plot location, intensity, and timing for more than 200,000 lightning flashes.
The final tally—which Van Eaton is confident is an underestimate—clocked a rate of about 2,600 flashes per minute at the height of the ring’s intensity. That’s a truly astonishing number, according to Eric Bruning, an associate professor of atmospheric science at Texas Tech University and wasn’t involved in the study.
A low-end, average thunderstorm might have a lightning flash every minute. In big supercell thunderstorms—the kind that make tornadoes—those will have flash rates in the hundreds per minute. [The rate of lightning in the Hunga eruption] is an order of magnitude higher.
The location data gives the Hunga event another superlative—lightning was recorded miles higher than ever thought possible, which researchers chalk up to the copious amounts of hot seawater injected into the atmosphere.
Surfing a gravity wave
Another unusual feature of the Hunga eruption is gravity waves, which occur when a trigger—such as a volcanic plume, composed of extremely hot volcanic gases, ash, and vaporized water—pushes air up or down.
These waves can be more buoyant than the surrounding atmosphere, which creates distinct layers, like oil and water.
Whereas an object would fall straight down after reaching its maximum height, in this case the plume is trapped above the layer of normal atmosphere—meaning as it falls, gravity forces the plume out horizontally, creating waves like ripples in a pond.
Riding the gravity wave are bits of tephra and vaporized seawater. As the water vapor rises high into the atmosphere, it rapidly cools, forming ice crystals and tiny pellets of soft hail called graupel. The ice bits accumulate static as they scrape past each other, forming what are essentially electrically charged “Dippin’ Dots,” Bruning says.
This “ice-charging” process is also how lightning forms during a normal thunderstorm; volcanic eruptions add the special sauce of “silicate charging” as tephra generate their own charge through a similar process. (See stunning photos of lightning.)
Van Eaton and her team argue that the leading edge of a gravity wave would be tailor-made for generating lightning. The sharp edge of the wave may separate particles by size—encouraging ash and tiny ice crystals to drift upward while denser particles like graupel or tephra slide down, like surfers on a wave. That helps form distinct areas of charge, setting the stage for lightning to correct the imbalance.
Bruning says the study authors have come up with a “compelling physical explanation” for a mysterious phenomenon that left volcanologists and meteorologists alike scratching their heads.
But there are still mysteries galore. As Van Eaton points out, there’s a point at which the lightning ring appears to dissipate—and then the donut hole backfills with thousands of flashes.
“We don’t have any answers” for the donut hole, Van Eaton says. “That’s going to be probably five Ph.D.s down the road.”
Why care about volcanic lightning?
Researchers say that tracking volcanic lightning could be an important tool for “nowcasting” eruptions—with potentially life-saving implications.
During volcanic activity, that thick plume makes it impossible for satellites to see whether an eruption has run its course or new jets of lava are still emerging. But as scientists learn more about how volcanic lightning forms, they can use real-time data to guide evacuations and public health decisions, says Cimarelli. “The rate of lightning can actually tell you if a new jet is coming out.” (Learn how volcanic lightning can warn of dangerous eruptions.)
Volcanic ash is hazardous to aircraft and communities downwind, adds Van Eaton.
“Any tools that we can bring to bear for earlier detection, for rapid characterization of what’s happening—that could impact airspace and people.”
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The eruption of the Hunga-Tonga-Hunga-Ha’apai volcano on 15 January 2022 was the largest recorded since the eruption of Krakatoa in 1883. The eruption triggered tsunami waves of up to 15m which struck the west coast of Tongatapu, ‘Eua and Ha’apai. Ashfall covered an area of at least five square kilometres.
Damage to the international and domestic undersea telecommunications meant little information was available from Tonga following the eruption. However, New Zealand Defence Force and Australian Defence Forces surveillance flights on 17 January showed significant damage to houses, roads, water tanks and other infrastructure on the west coast of Tongatapu, the Ha’apai island group and the west coast of ‘Eua. On 18 January, the Prime Minister of Tonga declared a state of emergency effective from 16 January. The Tongan Government and TRCS requested international assistance.
Only three direct and one indirect fatality have been officially attributed to the volcano and tsunami. Early government estimates were that 84,176 people (84 per cent of the population) on Tongatapu, Ha’apai and ‘Eua) were affected, particularly by ashfall. Around 3,000 people were displaced in the immediate aftermath, including some evacuated from seriously affected islands off the coast of Tongatapu and in the Ha’apai island group. Most subsequently returned to their communities, although some families evacuated from badly affected islands remain on Tongatapu.
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2022 Hunga Tonga–Hunga Haʻapai eruption and tsunami
| 2022 Hunga Tonga–Hunga Haʻapai eruption and tsunami | |
|---|---|
 Satellite animation of the initial ash plume and shockwave on 15 January 2022 | |
| Volcano | Hunga Tonga–Hunga Haʻapai |
| Start date | 20 December 2021[1][nb 1] |
| End date | 15 January 2022[1] |
| Type | Surtseyan, Plinian[3] |
| Location | Pacific Ocean, Tonga 20.550°S 175.385°W |
| VEI | 5–6[4] |
| Impact | At least 6 dead, 19 injured, and others reported missing, $90.4 million in damages in Tonga (estimated) |
In December 2021, an eruption began on Hunga Tonga–Hunga Haʻapai, a submarine volcano in the Tongan archipelago in the southern Pacific Ocean.[5] The eruption reached a very large and powerful climax nearly four weeks later, on 15 January 2022.[6] Hunga Tonga–Hunga Haʻapai is 65 kilometres (40 mi) north of Tongatapu, the country’s main island,[7] and is part of the highly active Tonga–Kermadec Islands volcanic arc, a subduction zone extending from New Zealand to Fiji.[8][9] In the Volcanic Explosivity Index scale, the eruption was rated at least a VEI-5.[1][10] Described by scientists as a “magma hammer”, the volcano at its height produced a series of four underwater thrusts, displaced 10 cubic kilometres (2.4 cu mi) of rock, ash and sediment, and generated the largest atmospheric explosion recorded by modern instrumentation.[6]
The eruption caused tsunamis in Tonga, Fiji, American Samoa, Vanuatu, New Zealand, Japan, the United States, the Russian Far East, Chile and Peru. At least four people were killed, some were injured, and some remain possibly missing in Tonga from tsunami waves up to 20 m (66 ft) high. Tsunami waves with run-up heights up to 45 m (148 ft) struck the uninhabited island of Tofua. Two people drowned in Peru when 2 m (6 ft 7 in) waves struck the coast. It was the largest volcanic eruption since the 1991 eruption of Mount Pinatubo, and the most powerful eruption since the 1883 eruption of Krakatoa.[11] NASA determined that the eruption was “hundreds of times more powerful” than the atomic bomb dropped on Hiroshima.[12] The eruption was the largest explosion recorded in the atmosphere by modern instrumentation, far larger than any 20th-century volcanic event or nuclear bomb test. It is thought that in recent centuries, only the Krakatoa eruption of 1883 rivalled the atmospheric disturbance produced.[13][14]
Volcanic activity
December 2021
After staying relatively inactive since 2014,[15] the Hunga Tonga–Hunga Haʻapai volcano erupted on 20 December 2021, sending particulates into the stratosphere. A large plume of ash was visible from Nukuʻalofa, the capital city of Tonga, about 70 km (43 mi) from the volcano.[1][16] The Volcanic Ash Advisory Center (VAAC) in Wellington, New Zealand, issued an advisory notice to airlines.[17] This initial eruption ended at 02:00 on 21 December 2021.[16]
On 22 and 23 December 2021, 8-to-14-kilometre-high (5.0 to 8.7 mi) plumes containing sulfur dioxide drifted to the north-north-east and spread over the Niuatoputapu, Haʻapai and Vavaʻu island groups. Surtseyan explosions, steam plumes and steam bursts were recorded by a Tonga Navy crew on 23 December 2021, during which time the first ground-based images of the eruption were created.[3]
Between 24 and 27 December 2021, steam and gas emissions reached altitudes of 10.3–12.2 kilometres (6.4–7.6 mi). Ash plumes reached heights of only 3 km (1.9 mi), depositing ash only adjacent to the volcano.[3] On 25 December 2021, satellite imagery revealed that the island had increased in size by 300–600 metres (980–1,970 ft) on its eastern side.[3][18] During 29–30 December 2021, several surges of Surtseyan activity occurred, some of which were witnessed by passengers on a small South Seas Charters boat. Eruption plumes during the second half of December 2021 interrupted air travel to Tonga multiple times.[3]
January 2022
As activity on the island decreased, it was declared dormant by the Tonga Geological Services on 11 January 2022.[2][19] A large eruption commenced on 14 January 2022 at 04:20 local time (15:20 UTC, 13 January), sending clouds of ash 20 km (12 mi) into the atmosphere.[20][21] The government of Tonga issued a tsunami warning to residents, and waves of 30 cm (12 in) were observed in Nuku’alofa. Later in the afternoon, Tongan geologists near the volcano observed explosions and a 5-kilometre-wide (3.1 mi) ash column between 17:00 and 18:30 local time. A much larger Plinian eruption started the following day (15 January 2022) at 17:14 local time (04:14:45 UTC, 15 January). The eruption column from this eruption rose 58 km (36 mi) into the mesosphere. The VAAC again issued an advisory notice to airlines. Ash from the eruption made landfall on the main island of Tongatapu, blotting out the sun. Loud explosions were heard 65 km (40 mi) away in Nukuʻalofa, and small stones and ash rained down from the sky. Many residents in Tonga were stuck in traffic whilst attempting to flee to higher ground.
The explosion was heard in Samoa, roughly 840 km (520 mi) away before the sound travelled to more distant countries. Residents in Fiji, more than 700 km (430 mi) away, described the sounds of thunder, while the “thump” of the eruption was also reported in Niue and Vanuatu. Tremors and shaking buildings were reported by residents in south-western Niue, around Alofi and Avatele. The United States Geological Survey estimated the eruption at a surface-wave magnitude of 5.8. The eruption was heard more than 2,000 km (1,200 mi) away in New Zealand, where the sound arrived two hours later.[35] A series of bangs were heard around 3:30 a.m. local time in and around Anchorage, Alaska, approximately 9,300 km (5,800 mi) away from the volcano, lasting about 30 minutes. Low-frequency noise persisted for approximately two hours. Booms were heard as far away as Yukon in Canada, 9,700 km (6,000 mi) away.
The volcanic explosion caused atmospheric shockwaves to propagate around the globe. Satellites visually captured shockwaves propagating across the Pacific Ocean and a very wide eruption column. The pressure wave was measured by weather stations in many locations, including New Zealand to a maximum amplitude of about 7 hPa, and Australia to 6.9 hPa at Lord Howe Island and 3.3 hPa at Perth. Even in Europe, a pressure fluctuation of 2.5 hPa was measured in Switzerland, and of just over 2 hPa when it reached the United Kingdom. Shockwaves were reported as having gone around the Earth as many as four times in Japan and Utah, and at least twice at the Blue Hill Meteorological Observatory in Massachusetts. The pressure shockwave was also observed in Chennai, India, which is 12,000 km from the eruption site.
Intense lightning activity was recorded during the eruption phase. The Vaisala Global Lightning Dataset GLD360 detected lightning in the form of radio waves. Several hundred to a thousand flashes of lightning were recorded by the system during the two weeks before the eruption. From 14 to 15 January 2022, tens of thousands of lightning flashes occurred. Between 05:00 and 06:00 UTC on 15 January 2022, 200,000 flashes were recorded.
Preliminary observations showed that the eruption column ejected a large amount of volcanic material into the stratosphere, leading to speculation that it would cause a temporary climate cooling effect. Later calculations showed it injected an estimated 400,000 tonnes of sulfur dioxide into the stratosphere and was unlikely to have any global cooling effect.[52] Despite this, the eruption had a cooling effect in the Southern Hemisphere, causing slight cooling of winters and spectacular sunsets. People living in the Southern Hemisphere experienced purple sunsets for a few months after the eruption. A cooling effect of 0.1–0.5 °C (0.18–0.90 °F) was expected to last until spring (September–November) 2022. The eruption was described as a once-in-a-thousand-year event for the Hunga caldera.
NASA satellite Aura detected the eruption using its microwave limb sounder. It measures ozone, water vapor and other atmospheric gases, and can penetrate obstacles such as ash clouds. The underwater explosion also sent 146 million tons of water from the South Pacific Ocean into the stratosphere. The amount of water vapor ejected was 10 per cent of the stratosphere’s typical stock. It was enough to temporarily warm the surface of Earth. It is estimated that an excess of water vapour should remain for 5–10 years.
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Academic research
According to a March 2022 paper in the journal Earthquake Research Advances, Hunga Tonga–Hunga Haʻapai’s plume reached a peak height of 58 kilometres (36 mi) into the atmosphere and sustained heights greater than 30 km (19 mi). The initial explosive event was possibly more powerful than the Hatepe eruption, even though Hatepe ejected over ten times the volume of material in a longer eruption. Hunga Tonga–Hunga Haʻapai erupted over a span of 12 hours, releasing 1.9 km3 (0.46 cu mi) of ejecta with an estimated mass of 2,900 teragrams.
The ERA paper says the eruption correlated to a VEI of 5–6. An April 2022 research paper led by Poli and Shapiro and published by the American Geophysical Union indicates that the eruption is the largest ever observed with modern instrumentation and estimates its VEI to be approximately 6. Meanwhile, Vergoz and others estimate the blast yield to be 100–200 megatons of TNT and place the corresponding VEI at 5.8. Likewise, a study by Diaz and Rigby estimates the energetic output of the eruption to be equivalent to 61 megatons of TNT, making the event more powerful than the largest nuclear bomb ever detonated (Tsar Bomba). The Smithsonian Institution Global Volcanism Program rated the eruption at VEI-5.
The ERA paper also concludes that this eruption resulted in the formation of a new caldera. In May 2022, scientists at the National Institute of Water and Atmospheric Research (NIWA) released a bathymetry map indicating a large caldera measuring 4 km (2.5 mi) in width formed from the eruption. Surveys also indicated that the caldera floor is located 850 m (2,790 ft) below sea level. According to a volcanologist, the caldera walls continue to experience ongoing collapses. Surveys of the seafloor around the volcano found large sediment piles, layers of fine mud and ash, and valleys up to 50 km (31 mi) from the volcano. The survey indicated that an estimated 6–7 km3 (1.4–1.7 cu mi) of debris was added to a 22,000-square-kilometre-area (8,500 sq mi) seafloor. Scientists also suggest that the volcano may still be erupting underwater.
A 2022 study in the journal Ocean Engineering by Heidarzadeh and others determined the size of the initial tsunami caused by the eruption. The study analyzed data from 22 tide gauges, eight Deep-ocean Assessment and Reporting of Tsunamis (DART) stations, eight atmospheric pressure time series, spectral analysis and computer simulation. It was concluded that the eruption displaced 6.6 km3 of seawater, 90 m (300 ft) in amplitude, with a length of 12 km (7.5 mi). The displacement generated a number of waves in the atmosphere, including lamb waves in the troposphere and gravity waves in higher layers of the atmosphere, which propagated around the world at speeds close to the speed of sound.
Hunga Tonga-Hunga Haʻapai in December 2021
Hunga Tonga-Hunga Haʻapai in February 2022, after the eruption
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Climate and atmospheric impact
The eruption produced a high eruption column, reaching elevations of 57 kilometres (35 mi) and thus reaching into the mesosphere; this is the highest known eruption column in history. The column developed multiple “umbrella”-like clouds, a higher one in the stratosphere and a lower at about 17 km (11 mi) elevation,[70] and generated a terrestrial gamma-ray flash. The column injected a large quantity of water into the stratosphere, where it disturbed the local temperature balance and caused the formation of anomalous winds.
Large volcanic eruptions can inject large amounts of sulfur dioxide into the stratosphere, causing the formation of aerosol layers that reflect sunlight and can cause a cooling of the climate. In contrast, during the Hunga Tonga–Hunga Haʻapai eruption this sulfur was accompanied by large amounts of water vapour, which by acting as a greenhouse gas overrode the aerosol effect and caused a net warming of the climate system.[73] One study estimated a 7% increase in the probability that global warming will exceed 1.5 °C (2.7 °F) in at least one of the next five years, although greenhouse gas emissions and climate policy to mitigate them remain the major determinant of this risk.
Tsunami
| Nuku’alofa Tonga | |
|---|---|
 Video of the tsunami waves hitting the capital, filmed by a resident, Mamani moe me’a fakaofō on YouTube |
Tsunamis are most frequently caused by earthquakes, while those caused by volcanic eruptions are rare. Fewer than 100 volcanic tsunamis were recorded in the prior two centuries. According to an official at GNS Science, the suspected cause of the tsunami was an undersea eruption that destroyed part of the island on 14 January. This allowed seawater to fill the volcanic vent, causing another undersea explosion the next day. The explosion was so huge that it penetrated through the overlying seawater and triggered the tsunami.
Importantly, the atmospheric waves caused by the explosion coupled to the ocean, generating additional tsunamis at large distances from the volcano; volcanic tsunamis normally do not reach far from the edifice. Tsunami forecast models and alert systems which were intended to work for earthquake-generated tsunamis failed to consider the effects of the shockwaves on the tsunami as it radiated outwards. Shockwaves from the eruption caused abnormally high waves along the coasts of Peru and Japan. The tsunami waves also struck the coasts earlier than had been forecasted.
Oceania
As a result of the eruption, a 1.2 m (3 ft 11 in) tsunami struck the Tongan capital Nukuʻalofa. Tide gauges in the city recorded waves 1.5–2 m (4 ft 11 in – 6 ft 7 in) in height. Videos posted on the Internet showed a series of waves hitting the shore and homes, sweeping away debris. Other videos show ashfall and a cloud of ash obscuring the sun. According to a resident in the Tongan capital, a series of initial smaller explosions was heard. It was followed by a tsunami approximately 15 minutes later. The first wave was said to be the largest. A long white wave was observed out at sea approaching the coast. Three waves reportedly struck the coast. In the wake of the tsunami, King Tupou VI was evacuated from the Royal Palace and traffic jams formed as locals fled inland or to higher ground.
The Tongan government, on 18 January 2022, confirmed waves of up to 15 m (49 ft) struck the west coast of Tongatapu, ʻEua and Haʻapai islands. Tsunami surveys along the Tonga islands confirmed that a tsunami of 20 m (66 ft) struck Nomuka, 65 km north-east of the island. An 18 m (59 ft) wave struck Kanokupolu, on Tongatapu. Waves measuring 10 m (33 ft) were reported on islands greater than 85 km away.[63] Satellite imagery, digital elevation models and synthetic aperture radar suggest tsunami runups of 45 m (148 ft) at the southern coast of Tofua. Coastal disturbances at the coast included landslides, debris fans and flows, and transported trees at elevations of 30 m (98 ft) to 70 m (230 ft) above sea level.
In Fiji, a tidal gauge in Suva recorded a wave measuring 20 cm (7.9 in) at 17:40 local time. Some tsunami activity was also reported in the Lau Islands. The islands of Moce, Moala, Kadavu and Taveuni were struck by low-level tsunamis that triggered flooding.
In American Samoa, a tsunami measuring 61 cm (24 in) was recorded by tide gauges. Niue, where residents evacuated coastal areas, reported no tsunami, despite tremors and the island’s close proximity to Tonga.
Tsunami waves of 1–2.5 m (3 ft 3 in – 8 ft 2 in) were observed in several islands in Vanuatu. The Vanuatu Meteorology and Geo-hazards Department said tsunami activity was expected to persist for the night of 15 January 2022. Waves up to 0.8 m (2 ft 7 in) in height were recorded in Hanalei, Hawaii.
A combination of a cyclone surge from Cyclone Cody and the tsunami caused extensive damage at a marina in Tutukaka in New Zealand. The waves pulled boats away from their moorings, taking some out into the bay and smashing some together, as well as damaging the structures at the marina. About eight to ten boats were completely sunk, with the total damage amounting to $5.93 million. According to Hauraki Gulf Weather, the tsunami struck on 16 January 2022 at between 01:05 and 01:10 local time on Great Barrier Island with a height of 1.33 m (4 ft 4 in). The tsunami caused flooding at Mahinepua Bay, where a campsite was located; all 50 individuals at the site were safe. A group of people fishing in Hokianga Harbour had to run for their lives to escape the waves, and reported having to drive through water over 1 m (3 ft 3 in) deep. Unusual waves were recorded in Port Taranaki in New Plymouth. They lasted 24 hours, with the largest having a peak-to-peak height of 1 m at 08:30 local time. There were no casualties reported in New Zealand.
In Australia, the Bureau of Meteorology said tsunami waves were observed throughout Saturday night on the shores along the east coast of Australia. Maximum tsunami waves of 1.27 m (4 ft 2 in) were recorded at Norfolk Island, 1.10 m (3 ft 7 in) at Lord Howe Island, 0.82 m (2 ft 8 in) at the Gold Coast, Queensland, 0.77 m (2 ft 6 in) at Twofold Bay, New South Wales, and 0.50 m (1 ft 8 in) at Hobart, Tasmania.
Asia
In Kominato, Amami, Kagoshima, Japan, a 1.2 m (3 ft 11 in) tsunami was reported at 23:55 on 15 January JST. At Tosashimizu, Kōchi, the tsunami was 0.9 m (2 ft 11 in) in height.[102][103] A tsunami measuring 0.9 m (2 ft 11 in) was also reported in Chichijima Futami. On the Tohoku coast, a 0.7 m (2 ft 4 in) wave struck at 00:38 local time, on 16 January 2022. In the Sendai Port, the tsunami measured 0.9 m (2 ft 11 in) at 00:08. In Iwate Prefecture, a 1.1 m (3 ft 7 in) tsunami was recorded at 02:26 on 16 January. The tallest tsunami was recorded 1.34 m (4 ft 5 in) at Amami Ōshima, Okinawa. Tsunami waves of less than a metre were reported along the Hokkaido Pacific coast. This was the nation’s first tsunami warning since the 2016 Fukushima earthquake. The JMA said that the tsunami struck 2.5 hours earlier than predicted. Small tsunami waves were observed on the coast of Taiwan. The heights of the tsunami were: 0.4 m (1 ft 4 in) at Houbi Lake in Pingtung County, followed by 0.38 m (1 ft 3 in).
On Orchid Island, Taitung County, 0.36 m (1 ft 2 in) in Yilan County, 0.31 m (1 ft 0 in) in Su’ao, and 0.29 m (11 in) at Hualien County. Waves were also observed at Chenggong with a height of 0.25 m (9.8 in), and at Kaohsiung for 0.24 m (9.4 in).
In Jeju Island, South Korea, there were fluctuations of up to 15–20 cm (5.9–7.9 in) in the sea level.
Russia’s Kuril Islands, in the country’s far east, had tsunami waves of about 20 cm (7.9 in).[111][112] At least two ports were warned.[112]
North America
The highest tsunami waves in the United States were 1.3 m (4 ft 3 in) in Port San Luis in San Luis Obispo County (Southern California) and 1.1 m (3 ft 7 in) in both Arena Cove and Crescent City (Northern California). Significant waves hit the Santa Cruz Harbor, and its parking lot was flooded with about 0.91 m (3 ft 0 in) of water, while Soquel Creek in the neighboring city of Capitola flowed backwards. A surfing competition was cancelled.[116] Strong currents in Half Moon Bay were reported,[114] while small waves were observed at Seal Beach. Waves up to 0.37 m (1 ft 3 in) in height were recorded in Nikolski, Alaska.
There was an unusually high tide along the coasts of British Columbia and Vancouver Island. At 11:55 am local time, the Pacific Tsunami Warning Center (PTWC) said tide levels rose 29 cm (11 in) in Winter Harbour. Large logs were pushed up by the high tides and deposited on the beaches.
The tsunami was first detected along the coastline of Mexico on 15 January at 12:35 by tide gauges at Michoacán. At the coasts of Guerrero, Oaxaca and Baja California Peninsula, sea level rise was reported with waves of 30 cm (12 in) to 61 cm (24 in). A tide level of 2.05 m (6 ft 9 in) was measured at Manzanillo, Colima, according to the Mareographic Service of the Institute of Geophysics of the National Autonomous University of Mexico. The tsunami had an amplitude of 1.19 m (3 ft 11 in) in Zihuatanejo. Waves of just under 1 m (3 ft 3 in) were recorded in Acapulco, Huatulco and Salina Cruz. Tsunami activity along the Pacific coast persisted until 20 January. The tsunami measured taller than 2 m (6 ft 7 in) at Ensenada, Baja California. Sea level disturbances were recorded at the coast of the Gulf of Mexico and Caribbean Sea. The shockwave-triggered meteotsunami had a maximum wave height of 0.377 m (1 ft 2.8 in).
Minor tsunamis were measured as far away as the Caribbean Sea and Texas, with National Oceanic and Atmospheric Administration (NOAA) reporting a maximum rise of 12 cm (4.7 in) at the Isla de Mona in Puerto Rico at 16:11 UTC. These may have been meteo-tsunamis related to slight atmospheric pressure changes.
South America
In Peru, two people were killed in Lambayeque, where the tsunami measured 2 m (6 ft 7 in). Waves measuring 0.68 m (2 ft 3 in) were recorded in the port of Callao, 0.72 m (2 ft 4 in) in Marcona District and 0.65 m (2 ft 2 in) in Paita.
Significant sea level disturbances were measured off the coast of Ecuador‘s La Libertad, Esmeraldas and Manta. At 2:33 am local time, a 50 cm rise in sea level was measured on the mainland. There were also sea level changes in the Galapagos Islands.[127] Sea level disturbances off the nation’s coast persisted for nearly an hour.
In northern Chile, waves of up to 2 m (6 ft 7 in) struck the coastline. Videos and images on social media from the Los Ríos Region showed the tsunami damaging piers, carrying boats and hitting beaches. A tsunami of 1.74 m (5 ft 9 in) was measured at Chañaral.
Impact
| Countries | Deaths | Injuries | Missing | Ref. |
|---|---|---|---|---|
| Tonga | 4 | 14 | Several | [171][172][173][174] |
| Peru | 2 | 0 | 0 | [125] |
| Fiji | 1 | Several | 0 | [175] |
| United States | 0 | 3 | 0 | [176] |
| Japan | 0 | 2 | 0 | [177] |
| Total | 7 | 19 | Several |
Tonga
Little information was made available on the extent of damage and casualties from Tonga due to communication issues involving a damaged undersea cable.[91] Video footage showing waves hitting coastal areas in Tonga was reported by Sky News.[178] Atatā, a small island off the capital city, was reportedly submerged and rescue operations were being carried out. Images confirmed that most of the island have been wiped out; the New Zealand Defence Force described the damages as “catastrophic”. There were some reports of residents in Tonga struggling to breathe as a result of the ash.
According to a media release by the government via a tweet, all structures were destroyed on Mango Island. Only two buildings remained intact on Fonoifua Island, and Nomuka Island suffered major damage. Twenty-one homes were destroyed and another 35 were seriously damaged on Tongatapu’s west coast. Eight homes were demolished and 20 seriously damaged in Nukuʻalofa. ʻEua Island saw the loss of two homes and 45 damaged.[87] An assessment by the United Nations Institute for Training and Research (UNITAR) revealed extensive damage on Atatā Island; at least 72 buildings were affected by the tsunami and the whole island was blanketed by ash.[182] Early reports said Atatā Island, which is located off the main Tongan island near Nukuʻalofa, was submerged by the tsunami. A Facebook post by the Royal Sunset Island Resort on the island said all residents were accounted for and safely evacuated. On Tongatapu, 50 homes were destroyed and 100 more suffered damage.
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A New Zealand government official in the capital Nukuʻalofa said extensive damage occurred on the waterfront of the city, as it was severely hit by the tsunami.[184] Acting High Commissioner Peter Lund said that several people were unaccounted for following the eruption and tsunami. Tattoo parlour owner Angela Glover, a British resident in Tonga, was among the people missing, swept away by the tsunami when it hit Nukuʻalofa. Glover’s body was later found. Though the extent of the damage in Tonga is still not clear, a blanket of thick ash has contaminated water supplies, cut off communications and prevented surveillance flights, making it difficult for relief efforts to begin. Another fatality was confirmed by the Ministry of Foreign Affairs and Trade on 18 January. Lund added that there was an initially unconfirmed third death from the tsunami. This third death was identified as a local resident, and the Tongan government has confirmed three deaths were the result of the tsunami. The Government of Tonga said that the two locals who died were from Mango and Nomuka islands, respectively. A fourth fatality was confirmed by 30 January, but information about this victim was not disclosed.
On 23 January, the Tongan government confirmed that eight people on Nomuka island were injured, with six others sustaining minor injuries.
Photos shared by a resident on the island of Lifuka, north-east of Nukuʻalofa showed minor damage to island communities and a wharf. Damage suggests the island was hit by smaller waves. The islands of ʻUiha and Haʻano also sustained limited damage from the tsunami. Several photographs showed debris left by the tsunami strewn across a road and on grass fields. Owners of the Haʻatafu Beach Resort wrote on Facebook that their beach resort, located at the northern tip of the island of Tongatapu, was completely destroyed. The employees were able to escape. They added that the whole western coastline of the island and Kanokupolu village were destroyed. The United Nations Office for the Coordination of Humanitarian Affairs stated that there was concern for two low-lying islands in the Haʻapai group, Fonoi and Mango, as a distress beacon had been detected on one of the islands (Fonoi has a population of 69 people, while Mango has 36 residents).[193] A surveillance flight confirmed “substantial property damage” on the two low-lying islands; the Tongan government later confirmed that all homes on Mango Island were destroyed.
Southern Cross Cable reported that the eruption may have broken the Tonga Cable System, which connects Tonga to Southern Cross’s trans-Pacific cable in Fiji.[196] Southern Cross cited a fault in the international cable 37 km (23 mi) from Nukuʻalofa, and a further fault in a domestic cable 47 km (29 mi) from Nukuʻalofa. New Zealand Prime Minister Jacinda Ardern had earlier stated that an undersea cable serving Tonga was affected, probably due to power cuts, and authorities were urgently attempting to restore communications. The chair of the Tonga Cable System, Samiuela Fonua, stated that repair crews would not be cleared to access the site of the faults before volcanic activity ceased at Hunga Tonga; with additional preparation time necessary for the repairs, internet services could be unavailable for over two weeks after the eruption. Limited satellite connectivity was established on 21 January, mobile phone provider Digicel established a 2G cell network on Tongatapu using a satellite dish from the University of the South Pacific.
Reuters reported that a specialist cable repair ship would arrive at the Tongan archipelago on 30 January. On 4 February, the Associated Press reported that Fonua stated that repair crews would need to replace 87 km (54 mi) of cable, and that he hoped to have it restored the following week. On 8 February, the Matangi Tonga website reported that more breaks were suspected within the cable, delaying the cable’s restoration to 20 February.
Agence France-Presse followed up in a report on 15 February, stating that the cable was torn into multiple pieces and that a 55-kilometre (34 mi) section of cable had been lost. The report also stated that separate sections of cable had been moved 5 km (3.1 mi) and buried under 30 cm (12 in) of silt. The cable being cut repeatedly and moved long distances is consistent with a turbidity current damaging it, similar to the 1929 Grand Banks earthquake. The cable connection to Tongatapu was repaired on 22 February.
Severe damage on the west coast of Tongatapu was confirmed by the New Zealand High Commission in Tonga on 17 January. Surveillance flights by the Australian Defence Forces reported extensive damage along the west coast. The shores of Nukuʻalofa had substantial damage as debris and rocks were deposited inland by the tsunami waves, according to an early report from the UN Office for the Coordination of Humanitarian Affairs (OCHA). A 2 cm (0.79 in) layer of volcanic ash blanketed the capital Nukuʻalofa.
Satellite images of Nomuka island showed that nearly a fifth of the structures had been damaged, with more than 40 buildings covered in ash. The Fuaʻamotu International Airport was covered with ash and dirt. There were also reports of water damage in the district of Nukuʻalofa. The Tongan navy that was dispatched to Haʻapai islands reported significant damage, where a tsunami estimated to be between 5–10 m (16–33 ft) in height traveled as far as 500 m (1,600 ft) inland.
The World Bank‘s damage assessment report for the Tongan Government stated that the eruption and tsunami caused damage estimated at US$90.4 million; ~18.5% of Tonga’s total gross domestic product (GDP). The Global Facility for Disaster Reduction and Recovery reported that 600 buildings including 300 homes were damaged or destroyed by the tsunami. The damage was estimated at US$43.7 million. At least 85% of Tonga’s agricultural industry was severely affected by damage to crops and fisheries, estimating at US$20.9 million. Damage to roads, bridges, ports and submarine cables were an estimated US$20.9 million. The clean-up cost is also an additional US$5 million.
By 23 February, Tonga Cable had managed to restore Tonga’s fibre-optic cable with the assistance of SpaceX. On 21 February, repair works on the Southern Cross Cable were completed, restoring Internet to Tonga.
Tongan Olympian flagbearer Pita Taufatofua, who became widely known during the 2016 Summer Olympics, gathered more than US$330,000 in aid to his native country, after he opened a GoFundMe fundraising website.
