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Exploding the volcanic mould

On January 15, 2022, 500 years of volcanology – the scientific study of volcanos – were “thrown out the window” in 100 seconds by the eruption of Hunga Tonga – Hunga Ha’apai and marine geologist Kevin Mackay can’t wait to tell you all about it.

National Institute of Water and Atmospheric Research [NIWA] scientist Mackay will visit Masterton this month, courtesy of Science Wairarapa, to share his passion for and knowledge of the Tongan underwater eruption – the biggest atmospheric explosion on Earth in more than 100 years.

He is programme leader for environmental information management at NIWA and in 2022 led an international team of 40, including 28 scientists from a range of disciplines, to investigate the eruption site.

“The critical thing is that all the evidence as to why this eruption was so violent is all underwater,” Mackay said. “So we went there by boat and then deployed all sorts of equipment.”

This included cameras, acoustic equipment, biological sampling gear, aerial drones and gliders – “little robots with wings, propellers, that use buoyancy to glide through the ocean. And they will just constantly sample the waters around it,” Mackay said.

The implications of the eruption are “huge” and so are some of the basic facts.

Mackay’s expedition found that almost 10 cubic kilometres of seafloor was displaced from the volcano’s summit and flanks and the crater is now 700m deeper than before the eruption.

Sediment cores from the sea floor show pyroclastic deposits of volcanic material at least 80km from the volcano.

No part of the volcano’s crater now remains above water and the eruption vastly reduced the size of the islands of Hunga Tonga and Hunga Ha’apai.

As well as geological and environmental impacts, it made the largest acoustic noise ever recorded and was heard audibly 10,000km away in Alaska.

“The atmospheric shockwave was so powerful, it went around the world three times,” Mackay said.

As well as official sources of data on the volcanic eruption, citizen science is also playing a role in unpacking what this volcano means for the planet.

“One of the things about this modern world is that there is actually now a proliferation of people with their own home weather station,” Mackay explained.

“So the atmospheric pressure wave caused by this was recorded globally by people in their home and they got on social media saying hey, look at this bang.”

“We’ve probably got another 50 or 60 years or more to just unpack the data and to work out what should the textbooks say. What are the implications for other volcanoes in the region and in terms of disaster mitigation?”

Kevin Mackay’s illustrated talk is at 7.30pm on Tuesday, September 12 at the Education Centre, 22 Dixon St, Masterton. All welcome. Door charge $5. Science Wairarapa is supported by Wairarapa REAP. An introduction to the talk is at https://niwa.co.nz/videos/mapping-the-tongan-eruption

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