Scientists have shed new light on a powerful undersea eruption north of New Zealand that proved larger than any on land in the past century.

In a just-published study, researchers have pieced together the 2012 eruption of the seafloor Havre volcano, which lies in the Kermadec Islands, about 1000km off the North Island.

The 2012 blow - the largest deep-ocean eruption of the past century - was revealed when satellite imagery picked up a pumice raft spread across some 400sq km of ocean.

"We knew it was a large-scale eruption, approximately equivalent to the biggest eruption we've seen on land in the 20th century," said the study's lead author, University of Tasmania volcanologist Dr Rebecca Carey.

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"Having the pre-eruption map of Havre volcano allowed us to know exactly what and where the new eruption products were on the submarine edifice.

"This event is a scientific goldmine as for the first time there are quantitative constraints on submarine eruption dynamics, and the role of the ocean in modulating those dynamics."

The volcano itself had been discovered only a decade earlier.

With 80 per cent of Earth's volcanoes located on the seafloor, the study of submarine volcanism was "very important", said Carey, who worked alongside Otago University's Professor James White on the study.

Volcanism was also an important source of heat and chemicals to the ocean, and supported life.

The pumice raft spread across some 400 sq km of ocean. Photo / Wikimedia Commons
The pumice raft spread across some 400 sq km of ocean. Photo / Wikimedia Commons

Over the two-year study, researchers used submersibles, including a remotely operated vehicle and an automated underwater vehicle, to map, observe and collect samples from Havre.

"There are conceptual theories about how deep volcanic eruptions should be relatively passive, forming lava flows due to the huge amount of pressure from the overlying water column," Carey said.

"This is the first event of high silica magma composition where we are able to provide the constraints that test whether the hydrostatic pressure did suppress explosivity.

"We were able to demonstrate that the eruption was very complex, involving more than 14 aligned vents that represent a massive rupture of the volcanic edifice.

A view of the ROV landing on the seafloor at Havre submarine volcano at 900 metres below sea level, in order to retrieve a heat flow monitor. The Remotely Operated Vehicle Jason is about the size of a large 4WD. Photo / Supplied
A view of the ROV landing on the seafloor at Havre submarine volcano at 900 metres below sea level, in order to retrieve a heat flow monitor. The Remotely Operated Vehicle Jason is about the size of a large 4WD. Photo / Supplied

"We were also able to demonstrate that 80 per cent of the volume of the pumice was delivered to the pumice raft and efficiently dispersed into the Pacific Ocean landing on Micronesian island beaches and the East Australian seaboard.

"The record of this eruption on Havre volcano itself is highly unfaithful - it preserves a small component of what was actually produced, which is important for how we interpret ancient submarine volcanic successions that are now uplifted and are highly prospective for metals and minerals."

Carey said data collected for the study has also led to much interest from the broader scientific community.

Havre volcano lies 1000km off the coast of the North Island. Photo / Supplied
Havre volcano lies 1000km off the coast of the North Island. Photo / Supplied

"The eruption blanketed the volcano with ash and pumice and devastated the biological communities.

"Biologists are very interested to learn more about how species recolonise, and where those new species are coming from," she said.

"We also discovered new infant hydrothermal systems, and observing how they recover after such a large event is of importance.

"There is a decade worth of interdisciplinary science to do based on our 2015 voyage data and samples," she said.

"It's very exciting to marry the geosciences with other scientific disciplines addressing novel research questions."

The study was published online in the journal Science Advances.