2025-05-05T19:37:17Z

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In January 2022, the underwater volcano Hunga Tonga-Hunga Haʻapai erupted with an astonishing and unprecedented force. Unlike many other well-known volcanic eruptions that occur on land, this particular event took place beneath the ocean's surface. This fundamental difference led many scientists to initially underestimate the eruption's significance and potential consequences.

However, new research is uncovering a startling reality: submarine volcanoes, such as Hunga, possess the capability to release forces powerful enough to cool entire hemispheres and substantially alter the upper atmosphere. This groundbreaking study, led by researchers from the University of Auckland in collaboration with experts from Tonga, reveals that the Hunga eruption produced effects that extended far beyond what was previously understood. It propelled vast quantities of steam into the atmosphere, prompting a reevaluation of how volcanic eruptions can influence the climate.

Traditionally, submarine eruptions have been perceived as secondary contributors to climate dynamics. The eruption of Hunga is now poised to change that narrative entirely, marking a significant shift in how we understand the impacts of underwater volcanic activity.

Hunga's Impact Was Underestimated

The influence of volcanoes on climate is largely due to their ability to inject gases and particles into the atmosphere. Historically, sulfur dioxide has been deemed the primary agent determining the cooling effects of volcanic eruptions. For example, the land-based eruption of Mount Pinatubo in 1991 released considerable amounts of sulfur dioxide, creating reflective aerosols that reduced sunlight and lowered global temperatures.

In contrast, the underwater Hunga volcano exhibited different behavior. It emitted far less sulfur dioxide than anticipated, leading some scientists to believe that its impact on climate would be minor. However, subsequent studies have shown that this assumption was profoundly mistaken. The effects of this submarine volcano have now been linked to measurable cooling across the Southern Hemisphere, along with a variety of unusual atmospheric changes.

Professor Shane Cronin, co-lead author of the study, emphasized, “Submarine volcanism has previously been overlooked in global climate studies, because there is typically not much atmospheric sulfur dioxide released.” Alongside postdoctoral fellow Dr. Jie Wu, Cronin's research challenges the long-held view that sulfur dioxide is the only critical metric in evaluating volcanic climate risk.

Three Billion Tons of Water Vapor Released

Instead of focusing solely on sulfur emissions, Hunga's eruption followed a different trajectory. It injected a staggering amount of water vapor—up to three billion tons—into the atmosphere within a mere hour. What is remarkable is that this vapor did not simply linger in the lower atmosphere; it ascended into the stratosphere and mesosphere, layers of the atmosphere that are infrequently influenced by terrestrial phenomena.

Water vapor in these upper layers has the capacity to trap heat and significantly affect weather patterns in intricate ways. This eruption has demonstrated that submarine volcanoes can impact climate not just through their emissions, but also by the impressive heights to which they can propel their materials.

“The eruption has been shown by several recently published studies to have cooled the Southern Hemisphere and caused a range of other atmospheric and climate impacts that we are still discovering,” Cronin noted, highlighting the ongoing research that is reshaping our understanding of underwater volcanic contributions to climate balance.

Where Did the Sulfur Go?

While the eruption had the potential to release a significant amount of sulfur dioxide, initial satellite data reported only modest levels of this gas. This discrepancy raised eyebrows, as one would expect a volcano of Hunga’s magnitude to produce more detectable sulfur. A deeper investigation revealed an underlying story that had significant implications.

Volcanic ash samples collected post-eruption helped unravel the mystery. Researchers found that the magma residing deep beneath the ocean surface—at depths ranging from 2.1 to over 5.6 kilometers—was rich in sulfur. Yet, when the eruption occurred between 400 and 1,000 meters below sea level, more than 93% of the sulfur never reached the atmosphere; instead, it dissolved directly into the ocean.

In total, the team's estimates indicated a release of 9.4 teragrams of sulfur, but nearly all of it bypassed the atmosphere entirely. This revelation suggests that traditional monitoring techniques, such as satellite tracking of sulfur levels and ice-core analysis, may have missed the actual extent of the event. The sulfur was indeed released; it simply took a path that went unnoticed.

Rapid Rise of Underwater Magma

The Hunga eruption was not only powerful; it was astonishingly rapid. Magma surged from the deep reservoir to the ocean floor in under three minutes. This swift ascent preserved microscopic chemical features, leading researchers to uncover the mingling of various magma types with sharp contrasts—approximately 1% differences—in water content. This finding points to complex storage and mixing processes that took place just prior to the eruption.

The eruption lasted a total of 11 hours, during which it released 319 teragrams of magmatic water. However, this figure pales in comparison to the volume of water vapor generated from the interaction between the magma and seawater. Remarkably, less than 10% of the total water vapor originated from the magma itself; the vast majority was a result of seawater vaporizing into steam, thus dramatically altering the atmospheric conditions above.

Invisible Yet Influential

The eruption's characteristics pose significant challenges for climate science. Because most of the sulfur entered the ocean rather than the atmosphere, the eruption left only a subtle trace in the air. This raises a pivotal question: how many volcanic events have been overlooked due to their lack of visible sulfur emissions?

This revelation carries profound implications. Submarine eruptions may be more common—and more relevant to our climate—than previously recognized. Unfortunately, without visible sulfur clouds, such events can easily slip under the radar in climate histories and predictive models.

Thus, it is possible that volcanic influences have been underestimated in historical contexts and miscalculated regarding future risks.

Wider Risks from the Underwater Volcano

Beyond their climatic implications, the Hunga eruption underscored additional dangers associated with submarine volcanic activity. Such eruptions can trigger massive tsunamis, disrupt undersea communication cables, and alter coastal environments significantly.

Cronin and his team, including researchers affiliated with the University of Otago, are continuing their collaboration with Tongan partners to gain a deeper understanding of the long-term effects of such events. “We are striving to understand the broader hazards of submarine volcanism, including tsunami risk, damage to shorelines, and internet data cables, as well as how these eruptions affect our environment and climate,” Cronin explained.

This ongoing collaboration is essential for Pacific nations as they prepare for potential future eruptions. It also highlights existing gaps in global monitoring systems. If a submarine eruption can have such significant climate and infrastructure impacts without prior warning, scientists and policymakers must rethink their strategies for tracking and responding to these events.

Transforming Our Understanding of Earth’s Climate

The Hunga eruption has not only shaken the ocean floor but also challenged the foundational assumptions of climate science. It has demonstrated that water vapor can serve as a driving force behind climate shifts, that sulfur can vanish into the sea—evading detection by satellites and ice cores—and that submarine volcanoes warrant significantly more attention than they have historically received.

As researchers continue to investigate the aftermath of Hunga, one thing becomes clearer: the deep ocean is home to more than just hidden mysteries. It holds the potential to shape the atmosphere above, influence global temperatures, and subtly rewrite the narrative of Earth’s climate history.

The study detailing these findings has been published in the esteemed journal Nature Geoscience.

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