Billions Of Marine Organisms Are Catching A Pumice Ride To Australia


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

Mick Hoult, one of the sailers on an expedition to Fiji with a giant piece of pumice encountered on the trip. SailSurfROAM

An enormous field of pumice, spewed out by a volcano near Tonga, is heading for Australia. Prevailing winds and currents should bring it to the Great Barrier Reef in seven to eight months. On board will be many microorganisms and scientists think they could bring aid to the world’s greatest reef system, currently hard-pressed by high temperatures and ocean acidification.

Landlubbers probably filled the first tales of floating stones as far as the eye could see with accounts of mermaids and the Kraken, but underwater volcanoes sometimes spew forth pumice stones so hollow they can float on water. Eventually, the stones fill with water and sink, but this can take many years because the holes can be so small that surface tension prevents water displacing gas trapped inside.


On August 15, adventurers onboard the Sail Surf ROAM catamaran voyage to Fiji reported they were passing through waters dotted with pumice, ranging from the size of marbles to basketballs. Large concentrations of pumice are known as rafts, even though they are made up of millions of stones, rather than a single sheet as the name might suggest.

The raft has been attributed to an underwater volcano eruption near Tonga in early August. The same volcano erupted in 2001.

For Dr Scott Bryan of the Queensland University of Technology, this was exciting news. Bryan has made a specialty of studying these events, which happen around every five years in the South Pacific. This eruption doesn’t look set to reach the size of one in 2012, which has been rated the largest deep-ocean eruption in history. The current size estimate for this raft is 150 square kilometers (60 square miles or 20,000 football fields), about a third of 2012.

However, Bryan thinks the timing of this event could make it particularly ecologically significant. “At the moment the pumice will be bare and barren but over the next few weeks it’s going to start getting organisms attached to it,” Bryan said in a statement. “Then they’re going to grow and diversify, to ultimately wash up here in Australia.”


Bryan expects the raft to pass coral-rich islands like New Caledonia and Vanuatu during peak spawning season. Some of the coral larvae will make a home in the holes in the pumice and be carried to the Great Barrier Reef where they will settle when their transportation sinks. For a reef facing its most severe crisis in 10,000 years, the arrival of new genetics, adapted to different conditions, could be just the boost it needs. On the other hand, shipping will need to take care lest the larger stones damage the hull, and smaller ones be sucked into propellers.

For Bryan, the eruption offers a chance to compare the composition of the pumice with material from 2001, which he analyzed in unprecedented detail. Bryan expects this will reveal whether this is left-over magma from the previous eruption or a new batch, offering insight into the causes of underwater eruptions.

Larissa Brill from Sail Surf ROAM compares the size of pumice samples she encountered sailing to Fiji. SailSurfROAM
The location of the raft over the last two weeks as it moves west through the South Pacific. QUT media