It floated into the collective consciousness in August, twice the size of Manhattan and probably powerful enough to exfoliate the feet of the entire world. The giant Pacific Ocean pumice raft was as mysterious as it was vast.

The world only knew of its existence thanks to Michael Hoult and Larissa Brill, two Australians who sailed into it while travelling by catamaran to Fiji. Photographs they took showed a mass of grey stretching as far as the eye could see.

At the time it was not clear exactly where the giant pumice raft had come from – and what would become of it.

But now its origins and fate can be guessed at. Research published in the Journal of Volcanology and Geothermal Research says it was created by the eruption of an underwater volcano off the coast of Vavaʻu, the second largest island in Tonga.

The volcano, known as Volcano F or by the number 243091, erupted between 6 and 8 August, the researchers said. Researchers from the Geomar Helmholtz Centre for Ocean Research, in Kiel, Germany, used satellite images to track the raft’s creation and journey across the Pacific.

Satellite imagery showed plumes of vapour and ash, indicating an eruption, which matched exactly with maps of the seafloor that showed the underwater volcano. The team then tracked the progress of the raft as it moved west across the ocean until mid-August.

The pumice raft is due to reach Australia, and parts of the Great Barrier Reef, in late January or early February.

In August, it had been hoped that the raft could help revive the reef, which is suffering from climate change-induced mass bleaching.

The pumice raft adrift in the Pacific Ocean. Photograph: Nasa Earth Observatory

A Queensland University of Technology geologist, Scott Bryan, said the rocky flotilla could pick up marine organisms and become a “potential mechanism for restocking” the reef, by “bringing new healthy corals”.

However, a range of experts say this is unlikely.

Professor Terry Hughes, the director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, says the raft is too small, and coral would have no way to detach from the pumice on to the reef.

The coral biologist Dr Rebecca Albright from the California Academy of Sciences agreed. In fact, she told Scientific American that the pumice may even “abrade the reef”.

Pumice tutorial:



1. The pumice raft is 1/2,000th the size of the #GreatBarrierReef

2. Corals only rarely settle on pumice. When they do, they can't get off.

3. About 25 billion corals still alive on the #GreatBarrierReef produce quite a few larvae. https://t.co/eNvVAq84tR https://t.co/KQq7DiwMPv pic.twitter.com/VJRHnrk6j3 — Terry Hughes (@ProfTerryHughes) August 26, 2019

The press release now says the pumice covers 150 sq km. The #GreatBarrierReef is 344,000 sq km. Any corals that might settle on the pumice can’t just jump off onto a reef. — Terry Hughes (@ProfTerryHughes) August 25, 2019

Hughes told Australia’s Science Channel: “Pumice floats, and corals don’t like to attach to something that’s bobbing around on the ocean … It doesn’t want to be attached to something that’s mobile.”

He added that the process would take years.

“There isn’t any mechanism for [coral] to get off the pumice … The only way they could do that would be to stay floating on the pumice for several years until they grow big enough to reproduce and produce another generation of larvae which, it’s often three of four years minimum for that to happen.”

Albright said that previous studies of pumice rafts found corals were less than 1% of life on the rocks.

“By the time the pumice reaches Australia, there is a diverse community of things living on it,” she said. “But will corals be major players? No, absolutely not.”

She added that the focus on the raft ignored the main reason for the reef’s decline.

“The reason the Great Barrier Reef is in the condition it’s in is because of climate change. We’d be kidding ourselves if we did not acknowledge that elephant in the room. A pumice raft is not going to fix it.”