Hunga Tonga Should Have Been Obliterated by 2021 Eruption. It Wasn't

The Hunga Tonga volcano remains mysteriously intact when it should have been obliterated by its recent violent eruption, scientists have found.

In December 2021, the Hunga Tonga-Hunga Ha'apai volcano began erupting. A few weeks later on January 15 this reached a climax that resulted in the biggest volcanic eruption on Earth in 30 years that caused a four-foot tsunami wave.

Scientists from New Zealand's National Institute for Water and Atmospheric Research (NIWA) went on a month-long expedition of the underwater volcano to see how it had changed following the eruption and found something "surprising and unexpected."

NIWA marine geologist Kevin Mackay said in a press release that they expected to find the volcano "obliterated," but found it to be quite the opposite. Mackay was "taken aback" by the findings.

Sea life Hunga Tonga
The Hunga Tonga volcano remains mysteriously intact when it should have been obliterated by its recent violent eruption, scientists have found. A picture shows thriving sea life caught by underwater cameras 80km from the volcano. NIWA-Nippon Foundation TESMaP

"With an explosion that violent—the biggest ever recorded—you would expect that the whole volcano would have been obliterated, but it wasn't," he said. "While the volcano appeared intact, the seafloor showed some dramatic effects from the eruption. There is fine sandy mud and deep ash ripples as far as 50 kilometers away from the volcano, with gouged valleys and huge piles of sediment."

The reason for this is not yet clear, however, it was not the only surprising finding.

While the volcano itself is "devoid of biology" as expected, scientists found pockets of wildlife thriving as close as 15 kilometers away.

Scientists believe surviving wildlife managed to escape the direct impact of the volcano by being just outside of the flows pathway, meaning they avoided the blanket of ash that accompanied the eruption.

The expedition's marine biologist, Dr. Malcolm Clark, told Newsweek that it is believed "some faunal communities" are unaffected because "the eruption was not uniform in its impact."

"Rather than the ash cloud and underwater eruptive debris spreading out in a consistent radial pattern, it was variable depending on where the caldera walls were breached and how current flows in deeper water were affected by the complex seafloor topography," he said. "So there were major impacts on the immediate flanks of the volcano, in the gouged areas where pyroclastic flows occurred, and in areas where ash deposition was thick. These were pretty barren of life. However, seamounts close-by that were outside the path of these eruptive effects were left largely unaffected, and so pockets of wildlife remain."

He said while they were "surprised" to find such a large number of remnant populations, they were also "very pleased."

"They give good insights into the type of communities that may have been on the volcano initially, and what might be able to recolonize impacted areas and begin the process of recovery," he said.

Hunta Tonga
A picture shows a three-dimensional map of the underwater Hunga Tonga volcano, created using NIWA multibeam data. NIWA-Nippon Foundation TESMaP

Scientists even found evidence that the volcano may still be erupting, observing a dense layer of ash in the upper water column surrounding it.

NIWA biogeochemist Dr. Sarah Seabrook said in a press release that this layer of ash will have a variety of impacts on the surrounding ecosystem.

"In the immediate aftermath of an eruption, volcanic ash fertilizes microscopic ocean algae thanks to the ash's concentration of nutrients and trace metals—in this case, there was a bloom of life so big that we could see it from space," Seabrook said.

"However, the unexpected persistence of the ash in the water column is creating prolonged impacts. For example, spikes in volcanic ash were coupled to the appearance of oxygen minimum zones—where oxygen levels in the water are at their lowest—which could have implications for important services provided by the ocean, such as food production and carbon sequestration."

Hunga TOnga
A picture of the 2021 Hunga Tonga eruption from space. The eruption was the biggest on earth for 30 years. NASA