People in parts of Papua New Guinea are facing an unusual problem. Floating volcanic rock is making boat travel difficult, blocking access to fishing grounds and disrupting daily life in coastal communities.
The source of the pumice is the ongoing Titan Ridge eruption from an underwater volcano in the Bismarck Sea. Since May 9, the eruption has produced vast amounts of pumice - a lightweight, porous volcanic rock that floats on the ocean surface.
Reports from Manus Province in the country's northeast describe chunks of pumice accumulating along coastlines and waterways in enormous "rafts" 2-5 metres thick. In some locations, residents report being able to walk where there was previously open water.
It's a strange sight, but not an unprecedented one. Submarine eruptions have produced similarly vast pumice rafts before, and the experience from those events suggests the disruption facing Manus communities could persist for months or even years, long after the Titan Ridge eruption itself has ended.
A lifeline cut off
For many Manus communities, small boats are essential for accessing fishing grounds, neighbouring villages, markets, schools and healthcare services. When those transport routes become difficult to use, the consequences extend well beyond inconvenience.
PNG's Disaster Minister Billy Joseph has described growing concerns regarding food security and access to essential supplies.
The ocean serves as the backbone of Manus livelihoods, providing daily sustenance and the primary source of income through seafood sales. In some villages, residents have begun manually clearing pumice from shorelines and waterways in an effort to restore access to fishing grounds and prevent longer-term damage to local fisheries .
A costly precedent from Japan
Titan Ridge is not the first submarine eruption to generate widespread pumice rafts.
In 2021, the submarine eruption of Fukutoku-Oka-no-Ba south of Japan produced large quantities of floating pumice that drifted to the Nansei islands including Okinawa. There, pumice clogged 71 harbours and marinas, damaged hundreds of vessel engines, disrupted ferry services and affected tourism and fishery industries.
The economic cost in the Okinawa Prefecture alone exceeded 515 million yen.
Japan had extensive transport infrastructure, alternative supply chains and substantial federal resources for clean-up and recovery. The cleanup effort employed heavy machinery on land and sea and removed more than 110,000 cubic metres of pumice from the ports and beaches at an additional cost of more than 1 billion yen .
Despite its scale, the cleanup was only somewhat useful. Most pumice rafts only washed away the following spring with the change in seasonal winds.
Why this could last for years
While pumice from the 2021 Fukutoku-Oka-no-Ba eruption caused major disruption to ports, ferries and tourism in Japan, reports from Manus highlight a different concern: the potential impacts on food security and livelihoods in communities that depend directly on the ocean. These impacts may persist far longer than people expect.
Even after the eruption ends, the pumice already floating on the ocean will continue to move through the region for months to years. To understand why, it helps to understand how pumice behaves.
Pumice forms when gas-rich magma erupts and rapidly cools. The escaping gas leaves behind countless tiny holes, creating a rock that can be porous enough to float.
Individual pieces of pumice lump together to form enormous floating rafts covering hundreds or even thousands of square kilometres.
Many people believe that floating pumice quickly becomes waterlogged and sinks. Research by my colleagues and I shows otherwise.
Previous submarine eruptions show some pumice can remain afloat for years. Ocean currents, winds, and storms can repeatedly redistribute pumice across large areas of the ocean, moving it between coasts and islands long after an eruption ends.
After the 2012 submarine eruption of Havre volcano north of New Zealand, pumice travelled thousands of kilometres across the Pacific, reaching Queensland about eight months later and even Tasmania more than a year afterwards. So even after the Titan Ridge eruption, we can expect the pumice already produced to float around the region for months or years to come.
An ecological toll, too
Humans won't be the only ones affected. Whole ecosystems may suffer.
Months after the 2021 Fukutoku-Oka-no-Ba eruption in Japan, scientists observed dead farmed fish with stomachs full of pumice, indicating that some species may mistake floating pumice for food. The same researchers also documented pumice rafts passing across fringing coral reefs, temporarily reducing light levels and physically colliding with shallow-water coral colonies.
Research following the 2022 Hunga Tonga-Hunga Ha'apai eruption in Tonga suggests another possible ecological impact. Satellite observations showed volcanic particles suspended in seawater reduced light penetration through the water column, potentially affecting coral reefs and other marine ecosystems that depend on sunlight.
Whether similar impacts will occur in Papua New Guinea is not yet known. However, these observations suggest the marine ecological effects may extend beyond the immediate disruptions.
For now, the immediate concern remains the disruption to fishing, water and food security, and boat transport for essential services in Manus Province. But the people of Manus are dealing with only the first stage of the problem.
Pumice rafts are an unusual volcanic hazard because their impacts do not necessarily end when an eruption stops. The experience from Japan is that once the pumice enters coastal waterways, there are few easy solutions.
Rebecca Carey does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
