This is the most comprehensive analysis of a very complex and large eruption that had far-reaching impacts across the Pacific Ocean and beyond. Our work involved a truly global scientific effort with 76 authors from 17 countries. The group’s expertise included seismology, acoustics, tsunamis, ionospheric perturbations, and volcanology.

Atmospheric pressure waves caused by the Hunga eruption varied in frequency from acoustic-gravity to audio range, and so there was a need for interdisciplinary collaboration and perspective. Similarly, the event was captured on a wide range of instrument types, each providing different information and constraints, further motivating the collaboration.

The 15 January 2022 Hunga eruption was the culmination of a period of eruptions that began a month earlier in December 2021. All of the eruptions leading up to the main explosive event were much smaller, and the impacts were confined to the area around the islands of Hunga-Tonga and Hunga Ha’apai, Tonga.

The main eruption was the largest recorded in the past few decades and the most comprehensively recorded by global monitoring stations - part of the reason for the high number of scientists involved in the paper.

Following the eruption, global pressure sensing instruments recorded a Lamb wave – an atmospheric gravity wave generated by large disturbances of the atmosphere, such as by volcanic eruptions or other human-made sources that temporarily change the natural flow of the atmosphere. Lamb waves travel horizontally, and so the wave circled the globe at least four times over the six days following the eruption. We have never been able to record such a wave in as much detail before, or for as long a time period. This pressure wave was exceptionally rare.

Adding to the rarity of the event, the interaction between the atmospheric pressure wave and the ocean contributed to the tsunami activity generated by the eruption, and aided tsunami waves to travel right around the Pacific Ocean and other bodies of water like the Caribbean and Mediterranean Seas. 

This Lamb wave signal was a once-in-a-century occurrence and a once in a career type of signal. We had to go back to the 1883 eruption of Krakatau to find a comparable signal and not just from a volcano. What is so amazing about that is the 1883 eruption of Krakatau volcano and the observation of the atmospheric signals in barographs at the time was what began the the field of volcano infrasound which I work in now.

Hunga volcano produced a variety of types of atmospheric pressure waves including the Lamb wave, infrasound (sound below human hearing), and even audible sound. This sound was heard in NZ and while the direct sound from the eruption wasn't heard in Alaska, the interactions of this variety of waves produced an audible signal there as well.

We measure the size of an eruption in a couple different ways, the traditional being through the eruptive volume. However, in terms of the atmospheric signals produced this eruption was larger than both the 1980 Mt St Helens (Lawetlat'la), and the 1991 Pinatubo eruption.

This work was a huge community effort with 76 of us from 17 countries and a variety of backgrounds coming together for an intense 1 month of analysis. This analysis brought up many questions and there are already several other projects that have been spawned from this collaboration. There will be years and years of work done on this eruption.