Massive underwater eruption layered coral reefs with ash and suffocated marine life

In 2022, the underwater Hunga volcano exploded, blasting ash 37 miles into the sky – the largest volcanic plume ever captured by satellites. What followed offered researchers a rare chance to see how the ocean floor responds to sudden, massive disruption.

Months later, scientists from around the world headed to the location of the eruption on a research vessel.

Onboard the ship, undergraduate student Marcus Chaknova discovered something unexpected: thick layers of volcanic ash coating the seafloor. The ash had suffocated deep-sea ecosystems that rely on fragile chemical exchanges to survive.

Underwater eruptions usually go unseen

“This was an extremely rare opportunity,” Chaknova explained. “Observing the mass movement of underwater sediment is something that hasn’t been studied much.”

Now a graduate student in Earth Sciences at the University of Oregon, Chaknova led a study that analyzed what the underwater eruption left behind.

Working with Professor Thomas Giachetti and 16 other experts from around the world, he became the lead author on a study that looked at how volcanic ash travels – and what it does to life underwater.

“We had scientists from every single time zone you could think of,” Chaknova said. His project needed expertise from the fields of marine biology, geochemistry, and micropaleontology.

Tracking ash from the volcano

The first step was to confirm that the underwater ash had indeed come from Hunga, located about 40 miles from Tonga’s main island in the South Pacific.

After an eruption, it can take weeks or even months for ash to fall through the water and settle on the ocean floor. As it drifts, wind and currents push it farther from the eruption site.

“One grain of sediment will take weeks or months to reach the bottom of the ocean. It’s like a leaf falling from a tree. Because of the wind, it might end up somewhere completely different,” Giachetti explained.

Back in the lab, Chaknova matched the ash samples to those found near the volcano. The grains were varied – some jagged and sharp, others rounded and smooth.

In some places, the sediment was more than a meter thick. Most of it was made up of very fine particles, around the width of a human hair.

What the eruption left behind

Chaknova discovered that much of the ash came from the volcano’s caldera walls and was carried away by fast-moving underwater flows – something like underwater avalanches.

Those flows were so powerful they damaged submarine cables and carved small canyons into the seafloor. The researchers even used the timing of power loss from those broken cables to calculate how fast the ash surged.

Using computer models, Chaknova plans to simulate how the ash moved and where it went. Giachetti said this research could change how scientists think about sediment movement in the oceans.

Deep-sea life suffocated

The underwater eruption didn’t just leave a geological footprint; it disrupted entire ecosystems.

In the deep sea, where sunlight doesn’t reach, life depends on chemosynthesis – organisms use chemicals like methane or ammonia from hydrothermal vents, instead of sunlight, to produce energy.

Roughly 90% of marine life lives on the seafloor, according to the World Wide Fund for Nature. After the eruption, much of that life was buried in thick sediment.

Some creatures like worms and anemones can survive brief burials, but this sudden wave of ash was too much.

Many deep-sea species are suspension feeders. They grab tiny particles of food from the water and filter them through their gills.

“With all the displaced sediment, these organisms are only grabbing sediment,” Chaknova continued. “That’s going to clog their gills, it’s going to clog their intestines, and that’s going to have a dramatic effect on their ability to create energy.”

Fallout from the underwater eruption

Chaknova’s early findings also show that ash made it all the way to Tonga’s coral reefs. At first, it caused a short-lived plankton bloom at the surface.

But as the ash settled, it threatened coral ecosystems that support larger marine life. When coral suffers, everything above it in the food chain is affected.

On top of the environmental consequences, the eruption of this underwater volcano also affected livelihoods for Tonga residents.

Fishing is a way of life in Tonga. According to the World Bank, about 82% of households rely on reef fishing in some way for income. Marine tourism accounts for more than 7% of Tonga’s GDP.

“Although this eruption occurred on the seafloor, there is a chain of both positive and negative effects,” Chaknova explained.

“The negative effects go farther than just losing power or Wi-Fi from submarine cables. This is some people’s livelihood. They need fish for food. Fishing is incredibly important for the economic and food security of Tonga.”

Warning for deep-sea mining

The study also has bigger implications. As the world turns toward clean energy, demand is growing for metals like copper and cobalt – many of which sit in potato-sized nodules beneath the ocean floor.

Private companies have approached small Pacific nations, including Tonga, with offers to mine these resources.

“The area where we collected the sediment is within the Kingdom of Tonga, and we found that they are very rich in minerals,” Chaknova said.

“A lot of companies are interested in collecting these minerals, and so this area that belongs to the Kingdom of Tonga will be up for bid, in coming years, for deep-sea mining.”

While commercial mining hasn’t started yet, researchers are urging caution. The plumes of sediment created by mining could be just as harmful as those created by volcanic eruptions – clogging gills, burying habitats, and destroying fragile ecosystems.

Chaknova’s work provides some of the only real-world data we have on what that kind of disturbance could look like.

The research gives scientists and policymakers a better understanding of what’s at stake – and what might be lost if we move forward without enough knowledge.

The full study was published in the journal Geochemistry, Geophysics, Geosystems.

Image Credit: NOAA

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