NIWA scientists analysing the aftermath of Tonga's record-breaking Hunga Tonga-Hunga Ha'apai (HT-HH) volcanic eruption in December have made "surprising and unexpected" findings.
During a month-long expedition, researchers expected the volcano to be obliterated, but upon discovery they soon found the volcano to be primarily intact.
NIWA marine geologist Kevin Mackey said he was completely taken aback by what his team discovered.
"With an explosion that violent – the biggest ever recorded – you would expect that the whole volcano would have been obliterated, but it wasn’t."
Mackay said it was the seafloor surrounding the volcano that saw a drastic change.
"The seafloor showed some dramatic effects from the eruption. There is fine sandy mud and deep ash ripples as far as 50 kilometres away from the volcano, with gouged valleys and huge piles of sediment."
And it wasn't just the discovery of the volcano still intact, in a "remarkable" revelation researchers found diverse populations of fish and other animals as close as 15km away from the volcano.
NIWA marine biologist Dr Malcolm Cark said the sign of healthy life is positive.
"Although the seafloor on the volcano is largely barren, surrounding seamounts have pockets of normal biodiversity, such as corals, sponges, starfish, and mussels, indicating the resilience of such marine ecosystems and giving some hope for recovery."
Clark added more work is needed before they can be confident of how the surrounding ecosystem will respond.
"These surviving animal communities indicate what kind of life may repopulate HT-HH."
NIWA scientists also tested the water column for physical and chemical characteristics, including temperature, nutrients and oxygen concentration.
They say preliminary data shows the water column is still in recovery with some airborne ash yet to settle on the seafloor.
The data also revealed that the volcano may still be erupting, with a dense ash layer found in the upper water column near the volcano.
NIWA biogeochemist Dr Sarah Seabrook said the continuation of ash seen in the water column has a myriad of impacts on the ocean ecosystem.
"In the immediate aftermath of an eruption, volcanic ash fertilises microscopic ocean algae thanks to the ash’s concentration of nutrients and trace metals - in this case, there was a bloom of life so big that we could see it from space."
NIWA researchers found Tonga's internet cable under 30 metres of ash and sediment as well as seven cubic kilometres of displaced material.
"The equivalent of five Wellington Harbours or three million Olympic-sized swimming pools - but there is likely more yet to be seen."
