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A new study has comprehensively mapped the immediate after effects of the 15 January 2022 volcano eruption of Hunga Tonga - Hunga Ha'apai, highlighting the risks of similar events.
The study, published in Nature Communications, is part of the joint international project, the NIWA-Nippon Foundation Tonga Eruption Seabed Mapping Project (TESMaP), which includes 13 partners from Tonga, New Zealand, Australia, Germany, the United States, and the United Kingdom.
New Zealand's National Institute of Water and Atmospheric Research (NIWA) said the eruption was the biggest atmospheric explosion recorded on Earth in more than 100 years, displacing almost 10km3 of seafloor, and generating a tsunami that sent shockwaves around the world.
Following the eruption, scientists from NIWA set sail on RV Tangaroa for a month-long voyage to collect geological data, video footage, seabed imagery and water column samples.
Using this information, they were able to show the far-reaching ocean impacts of such a large eruption, including the widespread loss of seafloor life.
They worked with the Department of Geology in Nuku'alofa, led by the Head Geologist and now the Ministry of Lands, Natural Resources, Geology and Survey, chief executive Taaniela Kula.
Kula said ongoing studies and research will continue as they and their overseas partners continue to learn from "a one of a kind eruption" that has held the world of volcanology in awe.
"It's the first of its kind to be recognised by the volcanology community - confirming that it's a new kind of volcano eruption," he told RNZ Pacific.
He said no one in the volcanology community had witnessed or had ever heard of such an eruption, blowing up from the seafloor and going beyond the atmosphere into the mesosphere, 58km above sea level.
"Most of the volcanology community and the science community were very interested in finding out what was the true cause, and the mechanism that created this enormous eruption, that was heard around the world four times," he said.
Kula and the government of Tonga wants study to continue so that the country and its people can be prepared for what could happen in the future.
NIWA biogeochemist and lead author of the study Dr Sarah Seabrook said in a statement that they had made discoveries never before seen, reshaping their understanding of the impacts of volcanic eruptions on ocean ecosystems.
"Just one example is the role of underwater mountains (seamounts) providing a sheltering effect from the powerful seafloor density currents that smothered much of the seafloor around the volcano, wiping out seafloor life in the area, but left the seamounts relatively unscathed," Dr Seabrook said.
"Such refugia have been reported on land, where vegetation and people have been sheltered, but not in the ocean. But survival after the initial event is only the first hurdle. The eruption causes dramatic changes to nutrient and oxygen levels in the water which could have feedbacks that we are yet to understand.
"We do not know the timescale over which the seafloor communities in the Hunga Volcano may recover, but we think it may be aided by re-colonisation of the life which survived near these seamounts. The only way to see if it has survived, and to what extent, is to revisit the area."
She said that most eruptions of submarine volcanoes go undetected or underreported with little data before or after eruptions.
Dr Seabrook said that there is still much to be learned about the 22 mapped volcanoes in the Kingdom of Tonga, along with hundreds more along the Tonga-Tofua-Kermadec Arc, and numerous others worldwide.
"Future monitoring, of both the volcanic edifice itself and the surrounding seafloor and habitats, is necessary to robustly determine the resilience and recovery of both human and natural systems to major submarine eruptions. It will also help more broadly assess the risks posed by the many similar submerged volcanoes that exist worldwide."
'Need for more research globally'
Dr Isobel Yeo is a volcanologist, and lead scientist of the UK part of this international programme, based at the National Oceanography Centre (NOC).
She believes ongoing studies needs to continue.
"This work has highlighted the potential of offshore volcanoes to produce immense eruptions that pose a serious threat to coastal communities and subsea infrastructure, and highlights the urgent need for more research on and monitoring of these volcanic systems, not just in Tonga, but globally," she said.
Dr James Hunt of the UK's National Oceanography Centre said international partnerships were key to the success of the research.
"This complex project required mobilisation of a vessel immediately after the eruption and brought together a truly multidisciplinary science team. This could only be achieved through international collaborations, underlining a need to work across borders to understand volcanic hazards," he said.
