Revealing the Eruption Cycle of Hunga Tonga-Hunga Ha’apai

Results from research conducted by a team from Hakkaido University has revealed yet more information about the eruption of the underwater volcano Hunga Tonga-Hunga Ha’apai, on January 15, 2022.

The back-projection analysis of seismic P-waves revealed correlations with eruptions observed by satellite (Kotaro Tarumi, Kazunori Yoshizawa. Earth and Planetary Science Letters. January 15, 2023). Image credit: Kotaro Tarumi, Kazunori Yoshizawa. Earth and Planetary Science Letters. January 15, 2023

The sequence of eruptions occurred in two main parts.

The first sequence began at 04:02 UTC on January 15, then escalated into major explosions at 04:15 UTC and 200 to 300 seconds after. The entire sequence lasted at least until 04:35 UTC. Satellite imagery recorded the dramatic ash cloud.

A second sequence of eruptions began about four hours later and continued from six to seven minutes, including a massive eruption at 08:31.

Kazunori Yoshizawa, Hokkaido University explained:

“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 worthwhile to investigate the mechanisms involved in such eruption cycles further.” 

The volcano generated seismic, tsunami and atmospheric waves that were recorded worldwide. Recent studies have estimated that it was one of the most energetic eruptions recorded by modern instruments. 

The team at Hakkaido University used “back-projection” analysis to successfully detect the locations and timing of multiple explosions, even though P-waves from each eruption overlapped and were masked by other seismic signals and noises.

The back-projection technique reverses the transmission of seismic signals to reveal details of a potential source that radiated seismic waves. It was originally developed and applied for imaging the source processes of large earthquakes, but is now proving equally applicable to large scale volcanic events.

January 7 – 17, 2022 satellite images Hunga Tonga-Hunga Ha‘apai via Earth Observatory NASA

Kotaro Tarumi said:

“Eruption episodes are difficult to analyse fully from seismic surface waves, but we have teased out more details using what are called teleseismic-P waves.”

These are seismic waves have travelled through the planet to locations distant from the eruption site. In this case, the team used seismic data collected from sites as far as at a 93-degree angle around the circumference of the planet.

One interesting finding was that significant explosive eruptions intermittently occurred at 270 to 280 second intervals, a frequency suggesting a resonance effect with the atmosphere and the Earth.

Click on this link to access the report, Eruption sequence of the 2022 Hunga Tonga-Hunga Ha’apai explosion from back-projection of teleseismic P waves, published in Earth and Planetary Science Letters

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