In January 2022, a calm patch of ocean near the Tonga Islands suddenly became explosively active. About a month after the activity began, the undersea eruption of Hunga Volcano occurred on an unprecedented scale, spewing ash into the water column and Over 30 miles highwhich spread quickly in billowing smoke for hundreds of miles.
The explosion was so powerful that it rang like a bell around the Earth, the shock wave circled the Earth multiple times and created a sonic boom that was heard as far away as Alaska, and the eruption also triggered a tsunami that devastated the Pacific coast and created record-breaking waves in Japan, North and South America, and Antarctica.
To their surprise, the scientists discovered that the eruption also had effects underwater, as described in a recent study in the journal Nature. Nature Communications Earth and the Environment.
The Tahi Moana hydrothermal vent, pictured here, was observed to be covered in up to six inches of ash in some places. Some species of snails and mussels in the area survived the eruption and its aftermath.
As part of a fortunately timed expedition, a team of researchers set sail in April 2022 for the Lau Basin, a vast undersea region where the two tectonic plates surrounding Tonga meet. Their goal was to study life around deep-sea hot springs, but when they arrived, they found the area littered with dead creatures.
“We expected to see very little fallout from the eruption, because the eruption was several months away, about 100 miles away, and over a mile deep,” said Shawn Arellano, an associate professor at Western Washington University who led the expedition with Roxanne Beinart, an associate professor at the University of Rhode Island. “So we were really surprised by the level of impact we saw.”
Through the eyes of an underwater robot, they witnessed a layer of ash up to five feet thick covering the ocean floor, something never seen before. Local animal populations, including vulnerable mussels and snails on the Red List of Threatened Species, were either buried alive or wiped out, unable to adapt to the dramatically changed environment.
Similar catastrophic events appear in the fossil record, but scientists rarely have the opportunity to collect real-time observations.
“There are very few recent observations of volcanic ash deposition in the ocean,” Beinart says, “but there are many examples where scientists are looking at similar events in the fossil record and trying to understand what happened.” The team’s observations provide a rare glimpse into the early stages of the volcanic ash deposition process.
Perhaps thousands or millions of years from now, scientists will study the fossils of creatures buried by the Hunga volcano’s eruption.
Sink or swim?
With their original goal of studying the ecosystem all but dashed, the team quickly pivoted to explore the underwater aftermath of the eruption. One of their more immediate discoveries overturned a long-held idea about what happens to some organisms after a similar event.
Fossil records show that crabs and other crustaceans often go extinct when their habitats are suddenly covered in volcanic ash. Scientists speculate that this is likely because it clogs the animals’ respiratory systems. But Beinart and Arellano’s team noticed that the crustaceans managed to survive Hunga’s eruption, scurrying around on the ash that had swept away so many other animals. The team is still trying to figure out why the crustaceans managed to survive so well against the odds.
The team also collected more vent animal larvae than expected, and Arellano speculates that the new sampling system could have led to even more, or that the event may have triggered the animals to spawn, which is known to sometimes happen after storms or other major disturbances.
“Or maybe it’s just normal for this area,” Arellano says, “because there hasn’t been much collection here before, we don’t have a baseline to compare it to.”
Dexter Davis (Western Washington University)
Of the samples the team collected, Arellano made his first documented observations. Alvini-Concha Snail larvae. These snails grow into the dominant species at hydrothermal vents in the Western Pacific and Indian Oceans, but no one has ever seen them before. These organisms harbor chemosynthetic bacteria in their tissues and get most of their nutrition via chemicals in the hydrothermal vent fluids.
