Tonga volcanic eruption had a much more devastating impact than we knew

In January 2022, the underwater Hunga Tonga-Hunga Haʻapai volcano erupted with astonishing force. Unlike many well-known eruptions on land, this one happened underwater. That single difference led many scientists to underestimate its impact initially.

But new research has revealed a startling truth: submarine volcanoes, like Hunga, can unleash forces powerful enough to cool hemispheres and reshape the upper atmosphere.

Led by researchers from the University of Auckland and Tonga, a recent study shows that Hunga’s eruption had far-reaching effects. It injected vast amounts of steam into the sky and reshaped what we know about volcanic climate influence.

Submarine eruptions were once seen as secondary players in climate dynamics. Now, Hunga is changing that narrative entirely.

Hunga’s impact was underestimated

Volcanoes influence the climate by injecting gases and particles into the atmosphere. Until now, sulfur dioxide was considered the major player in determining the cooling effects of volcanic eruptions.

Land-based eruptions, like Mount Pinatubo in 1991, released large amounts of it, forming reflective aerosols that reduced sunlight and lowered global temperatures.

But the underwater Hunga volcano didn’t behave like those eruptions. It released far less sulfur dioxide than expected. That led some to believe its climate influence would be minor. Yet the opposite has turned out to be true.

This underwater volcano’s impact has now been linked to measurable cooling across the Southern Hemisphere as well as other unusual atmospheric changes.

“Submarine volcanism has previously been overlooked in global climate studies, because there is typically not much atmospheric sulfur dioxide released,” said Professor Shane Cronin, co-lead author of the study.

Alongside postdoctoral fellow Dr. Jie Wu, Cronin’s work challenges the traditional view that sulfur dioxide is the sole metric for climate risk.

Three billion tons of water vapor

Instead of relying on sulfur alone, Hunga took a different path. It injected up to 3 billion tons of water vapor into the sky in just one hour.

That vapor didn’t just stay in the lower atmosphere. It rose all the way to the stratosphere and mesosphere – layers of the atmosphere that are rarely touched by earthly forces.

Water vapor in these upper layers can trap heat and affect weather patterns in complex ways. This eruption showed that submarine volcanoes can influence the climate not just by what they emit, but by how high they can push that material.

“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,” noted Cronin.

These ongoing discoveries are forcing a re-evaluation of the role underwater eruptions play in Earth’s climate balance.

Where did the sulfur go?

While the eruption had the potential to unleash a large amount of sulfur dioxide, satellite data initially reported only modest levels. That seemed odd for an eruption of Hunga’s scale. Further investigation, however, revealed a hidden story.

Volcanic ash samples collected from the eruption helped solve the mystery. Researchers found that the magma stored deep below the ocean surface – between 2.1 and over 5.6 kilometers down – was rich in sulfur.

But when it exploded, the eruption happened between 400 and 1,000 meters below sea level. At those depths, over 93% of the sulfur never reached the air. It dissolved straight into the ocean waters.

The team estimated a total release of 9.4 teragrams of sulfur. Yet almost all of it bypassed the sky entirely. This means that traditional monitoring tools, like satellite sulfur tracking and even polar ice-core analysis, missed the true extent of the event. The sulfur was there – it just took a different path.

Underwater volcano’s magma rose rapidly

The eruption wasn’t just powerful; it was also incredibly fast. Magma surged upward from the deep reservoir to the ocean floor in under three minutes.

That rapid ascent preserved microscopic chemical features. Researchers discovered magmatic mingling with sharp contrasts – about 1% differences – in water content between magma types. This revealed that complex storage and mixing processes occurred just before the blast.

The eruption lasted 11 hours in total. During that time, it released 319 teragrams of magmatic water. But even that number paled in comparison to the water that was created through the interaction between magma and seawater.

Less than 10% of the total water vapor came from the magma itself. The vast majority resulted from seawater flashing into steam – enough to transform the sky above.

Invisible but influential

Because most of the sulfur entered the ocean, the eruption left only a faint trace in the atmosphere. This poses a major challenge for climate science.

Many global records of past eruptions rely on atmospheric sulfur data, especially from satellite sensors or ice cores. If eruptions like Hunga leave no clear signal in these tools, how many have been missed?

These findings raise serious concerns. Submarine eruptions may be more common – and more climate-relevant – than previously believed. Yet, without visible sulfur clouds, they go uncounted in climate histories and models.

This could mean that volcanic influence has been underestimated in past centuries or misjudged in terms of future risks.

Underwater volcano poses wider risks

Beyond climate, the eruption highlighted other dangers. Submarine explosions can trigger massive tsunamis, damage undersea communication cables, and reshape coastal environments.

Cronin and his team, including researchers now based at the University of Otago, continue to work with Tongan partners to understand the long-term effects.

“We are striving to understand the broader hazards of submarine volcanism, including tsunami and damage to shorelines and internet data cables, as well as how these eruptions affect our environment and climate,” explained Cronin.

This collaboration is helping Pacific nations prepare for future eruptions. It’s also drawing attention to gaps in global monitoring systems. If a submarine eruption can impact the climate and infrastructure without much warning, scientists and policymakers will need to rethink how they track and respond to these events.

Changing the way we read the Earth

The Hunga eruption has done more than shake the ocean floor – it has shaken the assumptions of climate science.

It showed that water vapor can drive climate shifts. It proved that sulfur can vanish into the sea, where it can remain hidden from satellites and ice. And it confirmed that submarine volcanoes deserve far more attention than they’ve received.

As researchers continue to explore Hunga’s aftermath, one thing becomes clear: the deep sea holds more than secrets. It holds the power to shape the air above us, shift global temperatures, and quietly rewrite Earth’s climate story.

The study is published in the journal Nature Geoscience.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–