New research proposes a vastly different trigger caused Tonga's volcanic eruption in 2022.
The study by GNS Science and the Australian National University suggests the underwater eruption of the Hunga Volcano was a gas-driven explosion, instead of the result of magma and water reacting through the water column, known as a phreatomagmatic explosion.
The eruption, on 15 January 2022, caused a 58km high ash plume within minutes and a 2-3 km diameter steep-walled crater deeper than the Burj Khalifa Tower. It was so powerful it sent out atmospheric shock waves that promulgated the entire planet.
The study's authors concluded a gas-driven trigger is likely based on the eruption magnitude, the time sequence, the mass amounts of volcanic gas release, the remaining volcano structure and the presence of minerals formed through magmatic gas interactions with the surrounding rock.
"What we witnessed during this event was a Plinean eruption. These are the kind most people think of when imagining an erupting volcano - very intense, violent and sudden with extremely high ash columns," said lead author Richard Henley.
"Our model describes a process that explains how the accumulation of volcanic gases over the months leading up to the eruption could generate this scale of explosive energy."
The study suggests an eruption sequence as follows: a fluctuation of magma-derived reactive gases aggressively alters the rocks in the volcano core, creating a seal that blocks gas flow to the surface. This then increases the internal gas pressure and puts stress on the volcanic structure. Then the seal fractures, leading to an explosive release of compressed gas.
"Not only does the paper suggest that the Hunga Plinean eruption was gas-driven but proposes that this mechanism may be characteristic of all Plinean eruptions regardless of whether the volcano is oceanic or subaerial. If correct, a pause in gas discharge may act as a precursor of a large eruption event," lead author Richard Henley said.
"Understanding the cause of the eruption is important for volcano monitoring and risk preparedness, not just for the Tongan archipelago but for the numerous submarine volcanoes that sit within New Zealand's maritime estate," GNS co-author Cornel de Ronde added.
"The eruption at Hunga has opened our eyes."
GNS Science will lead an international marine voyage from 14 May to 12 June to Hunga Volcano to collect geological, geophysical and water column data inside the crater to further investigate the cause of the eruption.
