Hunga Tonga: the eruption that broke atmospheric records

How big was it, really?

The January 2022 eruption rated VEI 5 on the Volcanic Explosivity Index — the most explosive eruption anywhere on Earth so far this century. Numbers alone don't land until you place them, so here is the context from our own records: across 11,079 Holocene eruptions in the Smithsonian GVP dataset, only 181 reach VEI 5, just 52 reach VEI 6, and a mere 7 reach VEI 7.A VEI-5 event sits in roughly the top two percent of everything volcanoes have done in the last ~12,000 years. The vast majority of eruptions — more than 4,000 of those 11,079 — are a modest VEI 2.

That rarity is the first reason Hunga Tonga matters. The second is how it did it. The plume reached about 57 km(58 km in some analyses) — roughly 1.5 times the height of the 1991 Mount Pinatubo plume (~40 km) and the tallest ever measured in the satellite era, according to a University of Oxford study published in November 2022. It was the first volcanic plume ever directly observed punching into the mesosphere. See how it ranks among the all-time giants on our most explosive volcanoes leaderboard.

A volcano with a very quiet past

Here is what makes the 2022 blast so unsettling. Hunga Tonga–Hunga Haʻapai is a mostly submarine caldera — a ring about 6 km across whose only dry land, before 2022, was two small islands poking ~114 m above the waves on its rim. Our database holds just 7 eruptions for it, and before 2022 every graded one was small: one VEI 0 and four VEI 2. Then, in 2021–2022, it produced a VEI 5. A volcano whose whole known résumé was minor coughs delivered the most explosive eruption of the century.

It had done this before, long ago. The Smithsonian summary notes a caldera-forming eruption radiocarbon-dated to roughly 1040–1180 CE, with older pumice-rich deposits below it hinting at still larger events. The lesson geologists drew in 2022 is uncomfortable: an arc volcano can look harmless for centuries of small activity and still hold a caldera-scale eruption in reserve. The explosiveness comes partly from its setting — seawater flashing to steam against rising magma, a mechanism that can turn a modest batch of magma into a far larger blast.

The tsunami, the shockwave, and the water in the sky

What set Hunga Tonga apart wasn't just its size — it was the cascade of effects that reached far beyond Tonga. The eruption sent a tsunami racing across the Pacific that killed four people in Tonga and caused damage and deaths as far away as Peru. Unusually, it generated two kinds of sea waves: the normal eruption-driven tsunami, and a second set pushed by the atmospheric pressure wave, which outran the ordinary wave and reached ocean basins it could not.

That atmospheric pressure wave was itself historic. The blast launched a boom that was detected circling the entire planet multiple times over several days, a surface-to-space signature documented in Nature (2022). Barometers from Japan to the United Kingdom registered the pulse as it swept past — comparisons were drawn to the 1883 Krakatoa eruption, whose own pressure wave famously circled the globe.

Then there was the water. Because the eruption blew through the ocean, it injected an estimated 146 teragrams of water vapour— about 146 billion kilograms — into the normally bone-dry stratosphere, enough to raise the stratosphere's total water content by roughly 10%, and nearly four times the water Pinatubo delivered, per NASA's Jet Propulsion Laboratory. The fine particles that normally cause temporary cooling were there too, but it was the water — a greenhouse gas — that made this eruption's climate fingerprint so unusual.

Why scientists are still studying it in 2026

Four years on, Hunga Tonga is still generating papers — which is itself rare for a single eruption. The stratospheric water it injected has lingered far longer than the aerosols from a typical large eruption, and researchers have tracked its slow effects on stratospheric chemistry and circulation well into the late 2020s. As of 2026, studies examining the water-rich plume have reported evidence that chlorine chemistry inside it may have temporarily destroyed atmospheric methane — an entirely unexpected side effect of an undersea volcano.

That's the enduring significance: Hunga Tonga is the clearest modern case of a volcano whose biggest impacts were atmospheric rather than local. It reshaped how scientists think about what a submarine VEI-5 eruption can do to the sky. To see where it sits among history's heavyweights, our largest volcanic eruptions and volcanic ash explainers put the plume and fallout in context.

Hunga Tonga, quick answers