Tonga’s massive 2022 eruption was an `inside job’

Research led by the University of Auckland has revealed what caused the huge underwater eruption in Tonga in January 2022 with scientists finding the answer lay inside the volcano itself.

The eruption at Hunga volcano was the most explosive in more than 100 years. It sent ash more than 50km into the sky and triggered powerful tsunami waves across the Pacific.

The underwater volcano likely contained two distinct pools of magma, according to the scientists.

In the weeks before the main blast on 15 January, smaller eruptions came from a shallow upper magma layer, says Professor Shane Cronin of the School of Environment at Waipapa Taumata Rau, University of Auckland.
 

Cronin and Dr Jie Wu, also of the School of Environment, were lead authors of the paper published in the journal Earth and Planetary Science Letters. Co-authors were from Tonga Geological Services, University of Otago, South Korea, Italy, Australia and the US.

When the upper layer of magma in the volcano became depleted, there was likely a sudden drop in pressure allowing gas-rich magma to suddenly rise from below, says Cronin.
 

Gases in the rising magma rapidly expanded, and at the same time seawater entered the volcano through cracks. When hot magma met cold seawater, it caused violent explosions.

“So, the trigger wasn’t new magma rising from deep within the Earth,” says Dr Wu. “It was an inside job – the scale of the eruption resulted from pressure changes and structural collapse within the volcano itself.”

In the same issue of the journal, Wu, Cronin and their co-authors described creating a micro-model of the Hunga volcano magma system from a single volcanic “bomb” – a fragment of molten rock – deposited on the ocean floor.

About 20cm in diameter, the rock cooled at different rates from its rim to its core, with consequent changes in chemistry and crystal content.

The research was funded by entities including New Zealand’s Royal Society Te Apārangi and Ministry of Business, Innovation and Employment.