Fifteen minutes prior to the significant eruption of the Hunga Tonga-Hunga Ha’apai volcano in January 2022, two distant seismic stations recorded a seismic wave. Researchers now suggest that these early signals could be instrumental in monitoring potential eruptions in remote oceanic volcanoes.
The scientists believe that the seismic wave was a result of a crack in a vulnerable section of the oceanic crust located beneath the caldera wall of the volcano. This crack facilitated an influx of seawater into the magma, allowing them to mix in the area above the volcano’s magma chamber, thereby triggering a violent eruption.
This study was published in Geophysical Research Letters, an AGU journal known for its quick-access, high-impact reports across all fields of Earth and space sciences.
The findings expand on the researchers’ earlier work on monitoring volcanoes in remote locations. In this instance, a Rayleigh wave—a type of seismic wave that travels along the Earth’s surface—was detected 750 kilometers (around 466 miles) away from the volcano.
“Early warnings are crucial for reducing disaster risks,” stated Mie Ichihara, a volcanologist from the University of Tokyo and co-author of the study. “Volcanic islands can trigger tsunamis, posing a serious threat.”
Quiet signs before a fiery eruption
The Hunga Tonga-Hunga Ha’apai is an oceanic volcano located in the western Pacific within the Kingdom of Tonga. Its formation arose from the Pacific Plate being pushed down beneath the Australian Plate, creating magma that can lead to eruptions.
On January 15, 2022, the volcano erupted with unprecedented force, releasing the equivalent of 58,000 Olympic swimming pools worth of water vapor into the stratosphere, initiating an extraordinary lightning storm and causing a tsunami. This powerful eruption was preceded by a smaller one on January 14 and a month’s worth of eruptive activities beforehand.
While the exact onset of the eruption is debated among researchers, most agree that it began shortly after 4:00 Coordinated Universal Time (UTC). The recent study identifies a Rayleigh wave occurring around 3:45 UTC.
The researchers analyzed seismic data from the Rayleigh wave detected by equipment on the islands of Fiji and Futuna. Though Rayleigh waves are a normal indication of volcanic eruptions and earthquakes, the researchers believe this particular wave pointed to an earlier event and a potential catalyst for the massive eruption.
“Generally, eruptions are prefaced by seismic activity,” explained Takuro Horiuchi, a volcanology graduate student from the University of Tokyo and lead author of the study. “Nevertheless, these seismic signals are generally subtle and only detected a few kilometers from the volcano.”
In contrast, this seismic signal covered a substantial distance, which suggests that a significant seismic event was occurring. “We think that unusually large movements began with this precursor,” Horiuchi added.
Mysteries of the seamount
While scientists may not fully determine the exact reasons behind the enormous “caldera-forming” eruption, Ichihara contends that the process unfolded gradually. She proposes that the precursor event started an underground process eventually culminating in the eruption.
However, pinpointing the origins of these extraordinary eruptions can be quite challenging.
“There are very few documented caldera-forming eruptions, and even fewer have been observed in the ocean,” Ichihara remarked. “This provides one perspective on the processes leading to caldera formation, but there could be other scenarios as well.”
Nonetheless, spotting early eruption indicators could offer island nations and coastal communities critical time to prepare for potential tsunamis—even if the seismic signal isn’t felt at the surface.
“During the eruption, we didn’t consider using this type of analysis in real time,” Ichihara noted. “However, the next time there’s a significant underwater eruption, local monitoring stations might be able to detect it using their data.”
