A new analysis of seismic data recorded after the massively violent eruption of the Hunga Tonga-Hunga Ha’apai underwater volcano on January 15, 2022 consisted of two distinct sequences of events, according to a new study. Kotaro Tarumi and Kazunori Yoshizawa of Hokkaido University in Japan discuss their methods and findings in an article in Earth and Planetary Science Letters.
seismologist and geophysicist Yoshizawa said “We showed that the eruption consisted of two distinct sequences of events, some of which occurred quasi-periodically in the first sequence. It will be useful to further investigate the mechanisms involved in such eruption cycles”.
Tarumi said “the volcano generated seismic, tsunami and atmospheric waves that were recorded around the world. Recent studies have estimated that it was one of the most powerful eruptions recorded by modern instruments. Eruption eruptions are difficult to fully analyze from seismic surface waves, but we obtained more details using what are called teleseismic-P waves”.
These are seismic waves that traveled through the planet to locations far from the eruption site, the study said. In this case, the team used seismic data collected from locations up to 93 degrees around the planet’s circumference, the study said.
The team’s “backprojection” analysis successfully detected the locations and timing of several explosions, even though the P-waves from each eruption overlapped and were masked by other seismic signals and sounds, the study said.
The back-projection technique reverses the transmission of seismic signals to reveal details of the potential source that emitted the seismic waves. It was originally developed and used to image the source processes of large earthquakes, but is now being shown to be equally applicable to large-scale volcanic events, the study said.
The results showed that the sequence of eruptions occurred in two main parts. The first sequence began at 04:02 UTC on January 15, then escalated into large explosions at 04:15 UTC and 200 to 300 seconds thereafter. The entire sequence lasted until at least 04:35 UTC, the study said.
A second sequence of eruptions began about four hours later and continued for six to seven minutes, including a massive eruption at 08:31 UTC, the study said. Satellite images captured the resulting dramatic ash cloud from the first eruption sequence, but until now the exact details of the underwater events remained elusive.
One interesting finding was that significant explosive eruptions occasionally occurred at intervals of 270 to 280 seconds, a frequency indicative of a resonance effect with the atmosphere and Earth, the study said. “This apparent coincidence of the eruption cycle and the atmospheric resonance oscillation with the Earth could be coincidental, but it certainly deserves further investigation,” Yoshizawa said.
