Hidden in the Pacific, two very different volcanoes are forcing scientists to rethink what counts as “biggest.” Tamu Massif, a shield-like giant buried beneath the northwest Pacific, spent years miscast as a cluster of smaller features before researchers showed it behaves as a single volcano. Far to the south, the Hunga Tonga-Hunga Haʻapai system erupted in January 2022 with a blast that hurled material skyward and produced the most intense lightning ever recorded by modern instruments, raising new questions about how violent an underwater eruption can be.
Across these discoveries, a pattern emerges: the ocean has quietly hosted some of the largest volcanic events on Earth, yet instruments and conceptual models have only recently caught up. Comparing the slow-built bulk of Tamu Massif with the sudden fury of Hunga’s paroxysmal eruption makes it clear that “biggest” can mean sheer size, explosive power or environmental reach, and that traditional volcano models have often underestimated what happens under the waves.
Tamu Massif: the hidden giant
For years, geologists treated Tamu Massif as just one part of a complicated oceanic plateau, but detailed work has reframed it as a single, immense shield-like volcano. Geophysical profiles and rock sampling used by William Sager and colleagues showed that lava flows spread outward from a central region, behaving much like the broad, gently sloping shields familiar from Hawaii, only on a far greater scale, according to geophysical analyses. That structure means the massif is not a patchwork of small volcanoes stitched together; it is one continuous volcanic edifice, assembled by repeated outpourings of magma on the seafloor.
This giant sits within the Shatsky Rise oceanic plateau in the northwest Pacific Ocean, a region that formed where a powerful mantle plume met a spreading ridge, according to the same 2013 study. Its shield-like shape implies eruptions that were largely effusive, with lava flowing rather than exploding, which challenges the popular picture of underwater volcanoes as mostly small, steep cones. Within the context of that work, Tamu Massif ranks among the largest known single volcanoes on Earth by volume at the time of publication, showing that the seafloor can host volcanic structures that rival or exceed the biggest edifices on land, yet remain almost invisible without detailed mapping and sampling.
Hunga’s paroxysmal blast in 2022
Where Tamu Massif tells a story of slow construction, the Hunga Tonga-Hunga Haʻapai system is defined by sudden violence. The Hunga eruption on 15 January 2022 came from an andesitic submarine caldera, a type of volcanic depression where magma can interact intensely with seawater, according to a 2023 study of chlorophyll-a changes in the western South Pacific that examined the event as a case of andesitic submarine volcanism. Researchers in that study classified it as a paroxysmal eruption, meaning it involved an extreme, short-lived spike in explosive activity rather than a drawn-out series of smaller blasts, and they reported that the Hunga event was the biggest explosion in their chlorophyll-a dataset of explosive disturbances in the western South Pacific, not a global ranking.
Other observations place the blast in an even wider instrumental context. The Tonga Hunga volcano exploded violently on 15 January 2022, blasting about 10 cubic kilometers of rock, ash and sediment, equivalent to roughly 2.4 cubic miles, straight up from the seafloor, according to an analysis of the eruption’s lightning and plume structure that described how that volume of material was expelled. That work reported that the Tonga Hunga eruption was the biggest explosion recorded by modern instruments within its observational record, putting it in a rare class of events that can be compared directly using satellite, seismic and atmospheric data rather than historical accounts or indirect evidence.
Lightning, instruments and what “biggest” means
The 2022 Hunga event did more than move rock and ash; it lit up the sky with electrical activity on a scale not previously measured. The same analysis that quantified the 10 cubic kilometers, or 2.4 cubic miles, of ejected material also found that the Tonga Hunga volcano produced the most intense lightning ever seen in the instrumental record it considered, based on modern detection networks that track flashes and electrical power in storm clouds and volcanic plumes, as reported in a 2023 feature on the eruption’s lightning. By tying those lightning measurements to the eruption column’s growth, the study argued that the blast’s energy and the way ash and water mixed in the atmosphere created conditions for lightning that exceeded all previously recorded eruptions in that monitoring system.
This focus on lightning and instrumental records exposes a bias in how volcanic “size” is usually discussed. Tamu Massif, as a single, immense shield-like volcano within the Shatsky Rise oceanic plateau, is described in 2013 geophysical work as one of the largest known volcanic structures on Earth by volume at that time, yet it never produced a modern, instrumentally recorded blast like Hunga’s. By contrast, the Hunga eruption’s status as the biggest explosion recorded by modern instruments depends on the reach of those instruments, the specific detection networks used and the time window they cover, as described in analyses of the Tonga Hunga blast. Taken together, these findings suggest that “biggest” is often shorthand for “largest that current tools have caught in the act,” not necessarily the largest that has ever occurred.
From seafloor structure to ocean biology
One of the most intriguing scientific angles on Hunga’s paroxysmal eruption is how it affected life in the surrounding ocean. The study of chlorophyll-a concentrations in the western South Pacific treated the Hunga eruption from an andesitic submarine caldera on 15 January 2022 as a natural experiment, comparing it with other explosive events in the same region and time series. Because chlorophyll-a is a proxy for phytoplankton, the authors could track how microscopic marine plants responded to the sudden injection of ash, nutrients and heat, and they reported that the Hunga blast stood out in magnitude from any others they examined in that dataset, which shaped the biological signal they observed over several weeks after the eruption.
Set against this, Tamu Massif offers a very different kind of influence on the ocean. Its identification as a single, immense shield-like volcano within the Shatsky Rise oceanic plateau in the northwest Pacific Ocean means it has shaped the seafloor topography over a broad area, according to the 2013 Nature Geoscience study, but the available sources do not provide direct measurements of how Tamu’s bulk alters chlorophyll-a or other biological markers. The contrast instead highlights that effusive shield building and explosive caldera eruptions can influence the ocean in different ways: one by slowly reshaping the seafloor over millions of years, the other by sending a sudden pulse of material and energy through the water column and atmosphere on the scale of hours to days.
Rethinking submarine volcano hazards
Both Tamu Massif and the Hunga eruption expose gaps in how scientists and the public think about underwater volcanoes. The classification of Tamu Massif as a single, immense shield-like volcano came only after detailed geophysical profiling and sampling, according to peer-reviewed work on the massif published in 2013, which suggests that earlier models of oceanic plateaus may have underestimated how often the seafloor hosts truly giant individual volcanoes. At the same time, the identification of the Hunga eruption on 15 January 2022 as a paroxysmal event from an andesitic submarine caldera, and as the biggest explosion in the chlorophyll-a study’s regional dataset, challenges the idea that submarine eruptions are usually muffled by seawater and therefore less hazardous or energetic than their subaerial counterparts.
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*This article was researched with the help of AI, with human editors creating the final content.
