New trigger suggested for record-breaking 2022 Tonga eruption

The researchers suggest that the seismic wave resulted from the volcano breaking in a weak area of ​​ocean crust beneath the caldera wall. This rupture allowed seawater and magma to flow into the space above the volcano’s underground magma chamber and mix together there, explosively setting off the eruption.

The research was published on: Geophysical Research LettersAn open-access AGU journal covering all Earth and space sciences, publishing high-impact, short-format reports with immediate impact.

The results build on the researchers’ previous work monitoring remote volcanoes. In this case, a Rayleigh wave, a type of seismic wave that travels across the Earth’s surface, was detected 750 kilometers (about 466 miles) from the volcano.

“Early warnings are crucial for disaster mitigation,” said Mie Ichihara, a volcanologist at the University of Tokyo and a co-author of the study. “Island volcanoes can produce tsunamis, which are a significant hazard.”

Silent harbinger of a violent explosion

Hunga Tonga-Hunga Ha’apai is an oceanic volcano in the western Pacific Ocean in the Kingdom of Tonga. The seamount was formed by the subduction of the Pacific Plate beneath the Australian Plate, a process that produces magma and leads to eruptions.

On January 15, 2022, the volcano erupted with record-breaking energy, injecting the water vapor of 58,000 Olympic-size swimming pools into the stratosphere, unleashing an unprecedented lightning storm and creating a tsunami. This large eruption was preceded by a smaller eruption on January 14, and a month-long eruption activity before that.

Researchers are still debating the exact start time of the eruption, but most agree that the eruption began shortly after 4:00 a.m. Coordinated Universal Time (UTC). The new study reports a Rayleigh wave that started around 3:45 UTC.

Researchers used seismic data to analyze the Rayleigh wave, which was detected by instruments at seismic stations on the islands of Fiji and Futuna but was not felt by humans. While Rayleigh waves are a common feature of volcanic eruptions and earthquakes, researchers believe this wave is a precursor and possible cause of a major eruption.

“Many eruptions are preceded by seismic activity,” said Takuro Horiuchi, a volcanology graduate student at the University of Tokyo and lead author of the study. “However, such seismic signals are subtle and are detected only within a few kilometers of the volcano.”

In turn, this seismic signal traveled a large distance, indicating a major seismic event. “We believe that unusually large movements began around the time of the antecedent,” Horiuchi said.

secrets of the sea mountain

Scientists may never know exactly what caused the massive “caldera-forming” explosion; however, Ichihara believes that the process is not instantaneous. Instead, he thinks this precursor event was the beginning of an underground process that ultimately led to the eruption.

But the origins of these rare massive explosions can be difficult to pin down.

“Very few caldera-forming eruptions have been observed, and there are even fewer witnessed caldera-forming eruptions in the ocean,” Ichihara said. “This gives one scenario for the processes that lead to caldera formation, but I wouldn’t say it’s the only scenario.”

Regardless, early detection of eruption signals could give island nations and coastal areas more valuable time to prepare when faced with approaching tsunamis, even if the signal is not felt at the surface.

“We did not intend to use this type of analysis in real time at the time of the explosion,” Ichihara said. “But maybe next time there’s a significant explosion underwater, local observatories can recognize it from their own data.”