Something Weird Happened 15 Minutes Before the Giant Tonga Eruption of 2022

Two years ago, the Hunga Tonga-Hunga Ha’apai volcano blew its top, destroying the island of the same name, forcing mass evacuations, covering Tonga in ash, and causing several deaths. Predicting these sorts of natural disasters are exceedingly difficult, but a surprising new finding suggests some volcanoes give off a clue in the minutes preceding a cataclysmic eruption.

According to a team of researchers that reviewed some overlooked data from that data, the huge volcanic eruption that rocked the Pacific Ocean in 2022 was preceded by a seismic wave that shot across Earth’s surface. The data was collected by faraway seismometers, but the recent team posits that even those distant signals can help people prepare for future surprise eruptions.

Early warning systems for natural disasters—earthquakes, eruptions and tsunamis, as well as more predictable events like hurricanes, tornadoes, and typhoons—save lives. Any amount of notice is better than none, as even critical minutes of warning can make the difference between life and death.

“Early warnings are very important for disaster mitigation,” said study co-author Mie Ichihara, a volcanologist at the University of Tokyo, in an American Geophysical Union release. “Island volcanoes can generate tsunamis, which are a significant hazard.”

The team inspected seismometer data from stations in Fiji and Futuna—over 466 miles (750 kilometers) from the eruption. In that data, the researchers found a certain kind of surface-traveling seismic wave—called a Rayleigh wave—that emanated from the direction of the cataclysmic eruption about 15 minutes before the event itself. The Rayleigh wave was imperceptible to humans, but the seismometers had no problem picking it up.

“Referring to other seismic signals and satellite images, we concluded that the Rayleigh wave was the most significant eruption precursor with no apparent surface activity,” the researchers wrote in their work, published Monday in Geophysical Research Letters. “Including our findings and results of previous studies, we propose a scenario of the beginning of the caldera-forming eruption.”

The record-breaking eruption occurred on January 15, 2022. The eruption’s 36-mile-high (58-kilometer-high) volcanic plume was the largest ever recorded, and reached Earth’s mesosphere in just half an hour. The previous record-holder was the huge 1991 eruption of Mount Pinatubo in the Philippines.

As the team notes, the Hunga Tonga-Hunga Ha‘apai eruption was not preceded by any “apparent surface activity.” Consequently, the Rayleigh wave was the main indicator of the imminent destruction.

“When a usual earthquake occurs, seismic waves including the Rayleigh wave are instantaneously used to estimate the source parameters,” such as the epicenter, depth, magnitude, and mechanism, Ichihara told Gizmodo in an email. “Then, the source parameters are used to disseminate Tsunami early warning. However, there is no existing infrastructure to use the Rayleigh wave from an eruption precursor like the one identified in our article, though we believe it useful.”

In their paper, the researchers suggest that a fracture in the oceanic crust beneath the volcano’s caldera wall released the seismic wave detected in Fiji and Futuna. Then, magma from beneath the crust and ocean water above it poured into the volcano’s magma chamber beneath the surface, which caused the land above to collapse and kick off the eruption.

The team suggests that analyzing data from seismic stations located even hundreds of miles from an eruption can reveal the event before its worst impacts occur. “At the time of the eruption, we didn’t think of using this kind of analysis in real-time,” Ichihara said. “But maybe the next time that there is a significant eruption underwater, local observatories can recognize it from their data.”

Researchers are regularly finding new methods to spot potential disasters early. In 2021, a team of earth scientists found that tsunamis can be predicted by their magnetic fields, which arrive before the sea level changes that harken the arrival of the massive walls of water.

The Hunga Tonga-Hunga Ha‘apai eruption could have been much more disastrous if it occurred in a more populated part of the world. Hopefully, the insights gained from the record-setting explosion can help people better prepare for future events like it.