The magnitude of the intrusion is modest by volcanic standards. Stamps compares the volume to about 400 Olympic-size swimming pools, an amount that is not in itself a cause for alarm. The magma, according to the team’s numerical modeling, does not appear to be migrating closer to the crater, and the reservoir it is entering already existed prior to the event. Yet the significance of the finding extends well beyond the volume of rock involved. It demonstrates that the monitoring infrastructure installed on the volcano can detect subtle, transient deformation signals and, more importantly, that the team can interpret those signals with sufficient confidence to attribute them to specific subsurface processes. That capability lies at the heart of any credible early-warning effort for a volcano that alternates between gentle and violent behavior.

The detection itself was made possible by a ground-based geodetic network that Stamps’ group began building a decade ago. In 2016, the team installed six Global Navigation Satellite System instruments on the flanks and surroundings of Ol Doinyo Lengai. These continuously operating stations track the horizontal and vertical motions of the ground surface to a precision of about one millimeter, a level of sensitivity that allows researchers to distinguish genuine deformation of the volcanic edifice from noise introduced by atmospheric effects or equipment drift. The GNSS network is complemented by two broadband seismic stations that record earthquake activity across a wide range of frequencies, and the continuous instrumentation is supplemented by episodic benchmark measurements taken during field campaigns.

The combination proved decisive in 2024. When the GNSS stations recorded an uplift signal around the volcano, the team turned to numerical modeling to determine what subsurface source could reproduce the observed pattern of surface movement. By fitting deformation models to the geodetic data, the researchers concluded with a high degree of certainty that the signal was generated by an influx of magma into an already existing magma reservoir roughly three kilometers underground. The result validated both the sensitivity of the network and the interpretive framework the team has developed over more than ten years of observation at the site. The work was published on September 18, 2026, in Frontiers in Earth Science, with the DOI 10.3389/feart.2026.1881885.

Ol Doinyo Lengai occupies a singular position in volcano science. Its carbonatite lavas erupt at temperatures far lower than the silicate lavas produced by virtually every other volcano on the planet, and during quiet periods the volcano maintains an active lava lake that bubbles and flows effusively within its summit crater. This effusive behavior, however, is only half of the volcano’s personality. On average, Ol Doinyo Lengai produces an explosive eruption every 10 to 15 years, and these explosive episodes can pose serious hazards to the communities that live on and around its slopes. Stamps notes that the team expects another explosive eruption within their lifetime, and the central motivation of the research program is to give residents and authorities enough lead time to prepare and respond to evacuation decisions made by the Tanzania Geological Survey.

Understanding what distinguishes a benign magma intrusion from a precursor to violence is the crux of the forecasting problem, and the 2024 event provided a valuable calibration point. According to Stamps, the last time the volcano erupted explosively, the event was preceded by a magnitude 5.9 earthquake. That historical sequence suggests a set of warning indicators that the team now watches for: a significant earthquake followed by observable changes in surface deformation, and, most critically, evidence that magma is moving from a deeper storage zone to a shallower one over time. Such upward migration indicates that magma is ascending the volcanic conduit, and it is precisely the kind of progression that would elevate concern. The 2024 intrusion, by contrast, showed magma entering an existing reservoir without any sign of ascent toward the crater, which is why the team assessed it as low risk.

One of the most stubborn uncertainties in volcanology is timing. Some volcanoes erupt explosively every time they erupt, making their behavior relatively predictable once unrest is detected. Ol Doinyo Lengai is more complicated, alternating between effusive and explosive eruptions in a pattern that is not fully understood. A key reason the team continues to monitor the volcano intensively is to constrain this particular volcano’s time delay, the interval between detectable precursory activity and an actual explosive eruption. Every additional episode of recorded deformation, seismicity, and magma transport adds to a decade-long baseline of observations that gradually reveals how the volcano’s subsurface system transitions from storage to ascent to eruption. The longer and richer the record becomes, the more skillfully the team can match patterns of surface observation to processes occurring underground.

The monitoring effort at Ol Doinyo Lengai is also notable for its ground-based character. Satellite-based observations, including those contributed through NASA, provide valuable context and broad spatial coverage of deformation across the region. But Stamps emphasizes that her team is currently the only group conducting continuous ground-based GNSS monitoring and consistent ground-based seismic monitoring at the volcano. Ground instruments offer continuous temporal sampling and millimeter-level precision that orbital observations alone cannot match, particularly for small, short-lived deformation episodes like the 2024 bulge, which might be missed or ambiguously characterized by intermittent satellite acquisitions. The redundancy and complementarity of the two approaches strengthen the overall early-warning picture.

The practical payoff of this work accrues directly to the people who live in the shadow of the volcano. More than a decade of observations has given the team a substantially better understanding of which underground magma movements correspond to which surface signals, and that empirical link is the foundation of any effort to anticipate when the volcano is edging closer to an explosive eruption. For residents of the surrounding area, the difference between a well-instrumented volcano and a poorly instrumented one can be measured in the time available to act. The Tanzania Geological Survey, which holds formal responsibility for evacuation decisions, now has access to a continuously refreshed, quantitatively interpreted stream of deformation and seismicity data from one of the rift’s most active and most unpredictable volcanoes.

The 2024 bulge may have been modest, equivalent to 400 swimming pools of magma settling into a reservoir it already knew, but as a test of scientific and operational readiness it was passed convincingly. A transient deformation signal was detected in near real time, modeled rigorously, attributed to a specific source at a specific depth, and correctly evaluated as non-threatening. Each such episode sharpens the interpretive tools that will be needed when the volcano’s behavior changes in more consequential ways. Given the volcano’s average recurrence interval of 10 to 15 years between explosive eruptions, the question is not whether the next one will come but whether the warning signs will be recognized in time. On the evidence of this study, the instruments are in place, the baseline record is deepening, and the science of translating millimeters of ground motion into meaningful forecasts is steadily maturing at one of Earth’s most remarkable volcanoes.

Subject of Research: Magma intrusion and surface deformation monitoring at Ol Doinyo Lengai volcano in Tanzania

Article Title: Interpreting a volcano’s ‘bulges’ and predicting the next explosive eruption

Article References: Interpreting a volcano’s ‘bulges’ and predicting the next explosive eruption. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Ol Doinyo Lengai, volcano monitoring, magma intrusion, GNSS, Tanzania, explosive eruption, East African Rift, surface deformation, carbonatite lava, seismic monitoring, early warning system, Frontiers in Earth Science

Hunga volcano, which rises from the Tonga-Kermadec arc about 65 kilometres north of Tongatapu, had already signalled its unrest in December 2021, with a sequence of eruptions that built a small temporary island and peppered the surrounding sea with floating pumice. Then, in the early afternoon of 15 January local time, the system transitioned almost instantaneously into a climactic phase. Explosions tore through the shallow edifice, whose vent lay only a few tens of metres below sea level, and the resulting plume punched through the tropopause into the mesosphere, the highest volcanic plume ever reliably documented. What the new analysis makes clear is that the extraordinary violence of the eruption was tightly coupled to the structural failure of the volcano itself: as the eruption evacuated magma from a shallow reservoir, the roof of the system foundered, and the caldera floor dropped by hundreds of metres in a remarkably short interval.

The quantitative core of the study lies in the comparison of multibeam echo-sounder surveys. A regional bathymetric mapping campaign in 2016 had captured the pre-eruption shape of Hunga’s submarine flanks and summit in detail, and repeated surveys carried out in the aftermath of the eruption, together with additional high-resolution mapping, allowed the researchers to compute a precise difference map of the seafloor. The results show that the collapse removed on the order of several cubic kilometres of rock from the edifice, deepening the caldera and reshaping the inner walls. Vertical changes of as much as several hundred metres were measured across broad areas of the caldera floor, confirming that this was a coherent piston-like subsidence of the reservoir roof rather than scattered slumping of loose material on the flanks.

To place that structural change on a timeline, the team turned to the geophysical signals recorded as the collapse unfolded. Seismic stations around the Pacific recorded an extraordinary sequence of very-long-period signals, a slow, rhythmic pulsing superimposed on the eruption’s broadband shaking that previous work had linked to repeated pressure oscillations in the coupled magma-seawater system. The new study shows that these pulses align closely in time with the inferred stages of caldera subsidence, indicating that the collapse did not occur as a single instantaneous drop but proceeded in discrete steps as the caldera block settled incrementally onto the diminishing magma body. Hydroacoustic and barometric records, including the Lamb wave that swept around the atmosphere, provide independent timing anchors, allowing the collapse history to be synchronized with the eruption’s global signals.

The mechanics inferred from these data are consistent with classical models of caldera formation but with an emphatically submarine twist. As magma withdrew rapidly from a shallow reservoir, the overlying roof lost support and failed along ring-shaped fractures. Seawater flooded into the vent region, and the intimate mixing of magma and water drove the eruption’s exceptional explosivity, a process long recognized in theory but seldom observed at this scale. Crucially, the collapse itself may have sustained the eruption: each increment of subsidence decompressed the remaining magma, accelerating volatile exsolution and feeding the next explosive pulse. The result was a positive feedback between structural failure and explosive discharge that explains how a volcano whose vent lay underwater could outshine, in atmospheric effect, any eruption of the satellite era.

The volume budget that emerges from the study also resolves a puzzle about the eruption’s products. Estimates of the ash and pumice deposited on land, on the seafloor, and dispersed through the atmosphere fall short of the volumes implied by the erupted magma in some reconstructions, and the new accounting of collapse volume helps close that balance. The subsided caldera accounts for a large fraction of the material removed from the reservoir, while a substantial volume of fragmented juvenile rock remained trapped as dense deposits within the deepened caldera basin, never reaching the surface as visible ash. This partitioning matters for interpretation: it shows that the caldera acts as a sediment trap that can hide a large share of an eruption’s output from conventional tephra inventories, a bias that likely affects volume estimates at many submarine volcanoes.

Beyond Hunga itself, the findings sharpen hazard assessment for the dozens of shallow submarine volcanoes in the Tonga-Kermadec arc and in comparable settings worldwide, from the Aeolian arc to the Kermadec subduction system’s northern neighbours. Shallow-water vents are notoriously difficult to monitor, and Hunga demonstrated that such systems can escalate from low-level activity to a globally significant climax with little warning. The recognition that caldera collapse can proceed in rapid, stepped fashion within hours, generating devastating tsunami through both displacement of seawater by the collapse and by the pyroclastic flows that raced across the seafloor, gives tsunami modellers a concrete, physically grounded scenario to test. The Hunga event generated tsunami waves that claimed lives as far away as Peru, underscoring that submarine collapse hazards are not confined to the volcano’s immediate shoreline.

Methodologically, the study exemplifies the power of merging datasets that individually capture only fragments of a fast-moving natural experiment. Pre- and post-eruption bathymetry fixes the geometry of collapse; very-long-period seismology constrains its tempo; atmospheric pressure waves and satellite imagery bound the eruption’s explosive energy; and petrological work on the erupted juvenile clasts ties the geophysical record to the magma’s storage conditions and volatile content. None of these threads alone could distinguish between competing interpretations, such as phreatomagmatic excavation versus gravitational sliding, but together they converge on a coherent narrative of reservoir-roof failure synchronously coupled to explosive discharge. The approach offers a template that can be applied retrospectively to other recent submarine eruptions and prospectively in monitoring network design.

The 2022 Hunga eruption severed Tonga’s international submarine cable, blanketed agricultural land in corrosive ash, and displaced communities, even as the exact interplay of processes driving its ferocity remained uncertain for months afterwards. By demonstrating that the seafloor of the volcano collapsed with extraordinary speed during the eruption’s climactic hours, the new research closes a central gap in that understanding and turns a catastrophic event into a benchmark for volcano science. As mapping technology and ocean-bottom instrumentation spread across the world’s volcanic arcs, events like Hunga will increasingly be captured in real time, and the lessons recorded here, about stepped collapse, magma-water feedback and hidden deposit volumes, will shape both the science and the preparedness of coastal nations living above active submarine volcanoes.

The Hunga collapse also provides a rare modern analogue for historical events that shaped early volcanological thinking. The 1883 eruption of Krakatau in Indonesia, which likewise involved a shallow marine vent and generated deadly seaborne tsunami, has long been interpreted as involving caldera-scale destruction of the edifice, but it was documented only through aftermath surveys and eyewitness accounts. The minute-by-minute geophysical record assembled for Hunga offers what those earlier events never could: a direct, instrumentally timed view of how a volcanic edifice fails during a climactic submarine eruption, allowing reinterpretation of historical catastrophes through a modern observational lens.

The stepped character of the subsidence carries particular significance for seismologists. Very-long-period signals of the kind recorded during Hunga are produced by slow, volumetric pressure changes in shallow magmatic and hydrothermal systems, and their rhythmic repetition during the collapse suggests that each increment of roof failure perturbed the underlying magma-seawater system in a repeatable way. Such signals, once calibrated against the bathymetric difference maps, could in principle serve as real-time indicators that a submarine edifice is actively foundering, giving warning of tsunami potential while an eruption is still under way.

The study also illustrates how much of an eruption’s story remains hidden beneath the sea surface. Because Hunga’s vent lay underwater, much of the fragmentation, transport and deposition of juvenile material occurred out of sight, and only the combination of seafloor mapping and geophysical inversion could recover the full mass balance. This hidden component helps explain why eruption magnitude scales derived from atmospheric and tephra observations alone can underestimate submarine events, and why repeated bathymetric surveys should be treated as an essential component of post-eruption response in volcanic arcs.

For the Tonga-Kermadec arc specifically, the results underscore the value of baseline mapping. The 2016 pre-eruption survey proved decisive, and the study implicitly argues for systematic, repeated multibeam coverage of shallow submarine volcanoes before crises occur, since without such baselines the geometry of any future collapse would be irrecoverable.

Subject of Research: Rapid submarine caldera collapse during the 2022 climactic eruption of Hunga volcano, Tonga

Article Title: Rapid submarine caldera collapse during the 2022 climactic eruption of Hunga volcano (Tonga)

Article References: Ribó, M., Cronin, S. J., Park, S.-H., Garvin, J., Yeo, I. A., Clare, M. A., Watson, S. J., Kang, S.-G., Sielfeld, G., Slayback, D. A., Choi, Y., Jung, J., Yoo, J., Hutton, B., Stern, S., White, J. D. L., Brenna, M., Hunt, J., Mackay, K., … Kula, T. (2026). Rapid submarine caldera collapse during the 2022 climactic eruption of Hunga volcano (Tonga). Nature Geoscience. https://doi.org/10.1038/s41561-026-02099-7

Image Credits: AI Generated

DOI: 10.1038/s41561-026-02099-7

Keywords: Hunga volcano, Tonga, submarine caldera collapse, 2022 eruption, caldera formation, bathymetry, very-long-period seismicity, phreatomagmatic eruption, tsunami, magma-water interaction, volcano monitoring, Tonga-Kermadec arc