NZ-led team of scientists hope to understand why 2022 Tongan volcano was so violent

The submarine volcano that erupted near Tonga in January 2022 created the biggest atmospheric explosion in 100 years and the fastest underwater debris flow ever recorded.

Now a New Zealand-led team of scientists is on the way there onboard the research vessel R/V Tangaroa, hoping to find out why the blast was so powerful and help us prepare for future underwater eruptions.

Among scientists from eight nations onboard is Tongan geologist Pununu Tukuafu.

He was with the Tongan Geological Services near Hunga Tonga-Hunga Ha'apai monitoring the volcanic activity which had begun in December 2021.

"Me and my colleagues were out taking some drone images of the eruption at the time, so we could get a feel of what's going on," he said.

Days later came an explosion that not even scientists saw coming. It was an eruption so big, experts say it could have wiped Tonga off the map.

"[It was a] huge, huge eruption so far bigger than what we normally see - so that did take people by surprise," GNS Expedition Lead Cornel de Ronde said.

It's that violence and magnitude that's brought together the international group of scientists who are heading back to the eruption site to try and find out what made it so unique.

"We'll map the volcano and the sea floor, we'll do a lot of geophysics which tells us where the magma chamber is or how thick the lavas are and really set the scene as to why this volcano exploded so violently," de Ronde said.

A recently released study proposes the powerful eruption was caused by a gas-driven climactic explosion rather than a phreatomagmatic one - where magma and water react violently, as previously thought.

To further investigate the evidence supporting this theory, the expedition will collect geological, geophysical and water column data inside the volcano crater and over the flanks of the submerged eruption vent.

They'll conduct seven types of surveys, including seismic survey to understand the architecture of the volcano and the magma chamber.

"Because it blew out a hole from 200 below sea level to 850 below sea level, we effectively have a knife slicing through the stratigraphy of that volcano, like nature's own drill hole," de Ronde said.

"So we can get information about the evolution of the volcano through time."

They hope to bring together all of the pieces of the scientific puzzle to understand an event that's still a traumatic memory for many Tongans.

Tukuafu is excited to learn from the experts onboard.

"It's a great opportunity for me and my country and my workplace, because there's very little knowledge about volcanoes."

And although scientists can't predict when eruptions will happen, they hope volcanoes that are particularly dangerous can be identified, so communities around them can be prepared.

The voyage will include researchers from GNS Science, University of Auckland, Natural Resources Tonga, University of Genova, National Oceanic and Atmospheric Administration, GEOMAR Helmholtz Centre for Ocean Research Kiel, University of Toronto, and the Queensland University of Technology.

GNS Science's contribution to the voyage has been funded by the Beneath the Waves Endeavour programme, MBIE Strategic Science Investment Fund, Large Experiment Investment Fund and GNS vessel time allocated by the Tangaroa Reference Group.

Surveys to be undertaken by the R/VTangaroa:

  • Bathymetric mapping - establish if there has been any subsequent collapse of the volcano flanks, infill of the caldera and/or if new volcanic cones are forming inside the crater
  • Bathymetric, magnetic and gravity surveys - provide invaluable estimates of the volume of material displaced by the eruption, which will feed directly into tsunami modelling and other models focused on the 'why' and 'how' this eruption occurred
  • Seismic survey of the edifice and its surrounds - provide insight into the internal architecture of the volcano and may image the upper parts of the magma chamber, all the while providing structural evidence for the nature of the eruption
  • Dredging of the inner walls of the volcano - to recover both fresh and altered rock samples to gain a longer-term view of the petrological history (origin of rocks) of Hunga volcano, establishing triggers for the eruption and insight into magma conditions over time
  • Possible dredging of nearby satellite cones - to establish the petrology of the regional volcanic field
  • Water column surveys - ascertain whether there is ongoing volcanic activity at Hunga and to determine the extent and nature of seafloor hydrothermal activity on and around the volcano.