The cataclysmic submarine eruption of the Hunga volcano in Tonga in January 2022 stunned the scientific community with its immense power and far-reaching climatic consequences. Unlike typical volcanic eruptions of comparable magnitude, which are known for their substantial sulfur emissions driving atmospheric and climatic changes, this eruption displayed an unusual pattern: it injected colossal volumes of water vapor high into the atmosphere while expelling anomalously low amounts of sulfur dioxide. This paradox challenges conventional wisdom about volcanic processes and their impact on climate, prompting new investigations into the complex interactions occurring beneath the ocean’s surface during submarine explosions.
Volcanic eruptions are often measured by the volatility of their emissions, primarily sulfur dioxide (SO₂), which forms sulfate aerosols in the stratosphere and influences global temperatures by reflecting sunlight. The Hunga eruption, however, defied expectations by emitting comparatively meager sulfur quantities despite its enormous eruptive power. Researchers have long used satellite-based SO₂ monitoring to gauge volcanic hazards and their climatic repercussions, but the Hunga event revealed potential limitations in these methods, especially when eruptions occur underwater.
A recent study led by Wu, Cronin, and Brenna provides critical insights into these inconsistencies by examining volcanic ash samples collected throughout the eruption’s 11-hour duration. Their analysis sheds light on the volatile budgets—comprising water, sulfur, and other components—trapped within the erupting magma. The findings indicate that the magma feeding the eruption was stored within a vertically weakly stratified reservoir extending from roughly 2.1 km to more than 5.6 km beneath the seafloor. This stratification, or layering, suggests complex magmatic processes prior to eruption, likely influencing how gases and materials were partitioned.
One remarkable revelation concerns the rapid ascent of magma toward the surface. The data imply that magma rose through the oceanic crust and fragmented just 400 to 1,000 meters below sea level, accomplishing this remarkable journey in less than three minutes. This rapid ascent preserved micro-scale chemical mingling within the magma, manifesting as roughly 1 weight percent contrasts in magmatic water concentrations. The preservation of such fine-scale heterogeneities indicates turbulent yet surprisingly intact mixing processes during the magma’s rapid rise.
The enormous volume of water released from the magmatic source over the eruption is exceptional. The study estimates a total magmatic water release of 319 teragrams (Tg), representing less than 10% of the total water derived from interactions between magma and seawater. This discrepancy is pivotal: it underscores the dominant role of seawater in contributing water vapor emissions during submarine eruptions, a mechanism distinct from typical subaerial volcanic events. The dramatic influx of water vapor into the upper atmosphere, despite originating from an oceanic environment, has substantial implications for atmospheric chemistry and climatic feedbacks.
Sulfur emissions present a contrasting narrative. By comparing sulfur concentrations within magmatic glass and residual glass—not affected by degassing—the scientists calculated an overall sulfur release of 9.4 TgS (teragrams of sulfur). Strikingly, more than 93% of this sulfur was absorbed into the ocean rather than being injected into the atmosphere, largely due to the submarine fragmentation of magma occurring beneath the sea surface. This partitioning effectively "hides" sulfur emissions from atmospheric detection methods, such as satellite SO₂ sensing, which rely on atmospheric sulfur compounds for identifying volcanic activity.
The subdued atmospheric sulfur signals from the Hunga eruption suggest that submarine volcanic events may elude traditional volcanic surveillance techniques, potentially leading to underestimates of their true erupted mass and environmental impact. Furthermore, because sulfate aerosols derived from SO₂ oxidation are commonly deposited in polar ice cores—key archives for reconstructing historical volcanic activity and climate forcing—the minimal atmospheric sulfur release implies that submarine explosive eruptions like Hunga could be nearly invisible in such paleoclimate records despite their pronounced climatic effects.
This new understanding challenges existing frameworks in volcanology and climate science. The dominant climate influence of the Hunga explosion likely stems not from sulfate aerosols but instead from vast injections of water vapor, a potent greenhouse gas, into the stratosphere. While water vapor is short-lived compared with sulfate aerosols, its radiative forcing effects can be strong and highly variable, especially when injected directly into the upper atmosphere. This mechanism broadens the spectrum of volcanic-climate interactions, necessitating revised models that incorporate submarine eruptions and seawater-magma interactions more explicitly.
Magma-seawater interactions pose intriguing geochemical dynamics. When rising magma mingles and fragments underwater, it entrains vast quantities of seawater, which rapidly alters the degassing pathways and volatile release patterns. The suppression of sulfur degassing and enhanced water vapor production typify this process, demonstrating the unique environmental imprint of submarine eruptions. This finding also highlights the importance of detailed petrological and geochemical analyses of volcanic glasses to decipher volatile histories in submarine environments.
The rapid ascent and shallow fragmentation of magma beneath the seafloor create turbulent mixing zones where seawater and magma chemically interact in complex ways. These interactions may generate unique eruption styles and influence eruption intensities, durations, and the nature of volcanic plumes. These factors remain underexplored relative to their subaerial counterparts, signifying a frontier in volcanological research with broad implications for hazard assessment and volcanic monitoring.
From a monitoring perspective, the submarine Hunga eruption exemplifies the challenges of detecting and quantifying submarine volcanic emissions via remote sensing. Satellite instruments primarily detect atmospheric SO₂ plumes and ash clouds; however, underwater explosions may inject most sulfur into the ocean and release limited detectable SO₂, producing muted atmospheric signals. These limitations emphasize the need for multidisciplinary observational strategies combining seafloor measurements, ash sampling, satellite meteorology, and atmospheric chemistry to fully capture submarine volcanic phenomena.
Climate models will need to update their parameterizations of volcanic forcing by incorporating the distinctive volatile emissions from submarine eruptions. The study’s quantification of water and sulfur emissions provides a baseline for simulating these eruptions’ radiative impacts more accurately. Considering that submarine volcanism accounts for a significant fraction of global magmatic activity, albeit often hidden beneath the ocean, ignoring their climatic role could result in underestimated or misattributed volcanic climate impacts over various temporal scales.
In summary, the 2022 Hunga eruption serves as a seminal case study illuminating the interplay between submarine volcanism, volatile emissions, atmospheric chemistry, and climate forcing. The starkly low sulfur emissions contrasted against unprecedented water injections into the upper atmosphere redefine how scientists interpret volcanic signals and assess their environmental significance. These insights propel a paradigm shift in understanding submarine volcanic eruptions as potent yet partially concealed contributors to Earth’s dynamic climate system.
Further investigation into submarine volcanic eruptions will enhance our ability to forecast their environmental and climatic repercussions. Continued refinement of volatile budgets, eruption dynamics, and gas exchange mechanisms in submarine settings is essential for comprehensive volcanic hazard assessment, climate modeling, and interpretation of geological records. Ultimately, the Hunga eruption underscores the interconnectedness of oceanic and atmospheric processes and the need to integrate submarine volcanic phenomena within the broader narrative of Earth system science.
Subject of Research: Volcano volatile emissions, submarine eruption dynamics, magma-seawater interactions, climatic impact of underwater volcanic explosions.
Article Title: Low sulfur emissions from 2022 Hunga eruption due to seawater–magma interactions.
Article References:
Wu, J., Cronin, S.J., Brenna, M. et al. Low sulfur emissions from 2022 Hunga eruption due to seawater–magma interactions. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01691-7
Image Credits: AI Generated
