At 1.26 am on 19 July 2012, a satellite image captured a vapour plume in the Pacific Ocean, 1000 km north-east of New Zealand. Stranger still, there was a mysterious blob on the ocean's surface, an enormous grey-brown slick and it was spreading.
Scientists began to suspect that, far from human eyes and deep below the water's surface, an enormous volcanic eruption had occurred.
The great grey morass on water's surface was a huge raft of floating debris spewed from the bowels of a volcano on the seabed. This comprised trillions of pieces of pumice, mostly tiny fragments but some as large as a basketball - as ships that encountered the raft would later discover. In one day, the volcano ejected enough material to cover 400 sq km at a depth of 3.5m. It is thought to be the largest deep water (500m below sea level or more) eruption ever recorded below.
- One mile down, iron-rich waters, toxic fluids, and 81°C acidic vents made this volcano seem uninhabitable – yet scientists filmed something staggering
- It’s almost twice the size of Washington state and stretches 18 miles down into the Earth’s crust – and it’s underwater too
Pumice is a very low density, lightweight rock that forms when molten igneous rock is violently ejected from a volcano under extreme pressure and cools and depressurises rapidly, creating a frothing, bubbly like texture as it hardens. Air is trapped and sealed within the rock and so it floats easily.
The volcano in question is the Havre Seamount, and was only known before 2012 through sonar maps. It is a caldera, a broad volcanic basin rising 1000m from the sea floor with a diameter of 4.5-5km and ringed by steep walls. Its summit is some 650-720m below the sea's surface. After the eruption, fresh sonar mapping revealed that the submarine volcano had developed a distinct cone.
Havre Seamount lies on a great fault where a huge chunk of the Earth's crust known as the Pacific Plate sinks (subducts) beneath the Indo-Australian Plate on a line known as the Kermadec Arc. Water and other volatile compounds are dragged under at the same time and feed the volcanic activity. The Kermadec Islands, a loose chain of isles north-east of New Zealand, lie on the Arc and are volcanic in origin.
- It was twice the size of Manhattan and incredibly floated a colossal 3,000km across the ocean, transporting millions of animals on the way
- “I screamed before the rest of it came into the screen.” Deep-sea scientists film rare creature deep in Pacific Ocean
- "It produced a 12km high eruption plume, a large volume of floating pumice, and an island almost a mile-wide with cliffs 30-50m high"
Wind and ocean currents began to disrupt the pumice raft and it split into small rafts and long ribbons of material, which eventually covered over 550,000 sq km of the Pacific Ocean. This can be problematic for shipping as the pumice fragments can damage propellers or be clog seawater intakes that help with cooling larger vessels. In 2021, the Fukutoku-Okanoba undersea volcano some 1200 km south of Tokyo erupted masses of pumice pebbles that damaged tourism, fisheries and harbours in Japan and the Philippines.
Eventually the Havre pumice raft dissipated. Some of the pumice was washed up on the shores of Pacific islands, northern Australia and New Zealand. Though most pieces gradually absorbed water and eventually sank to become part of the ocean floor, it is very likely that some remained floating for many years after – and a few could still be adrift in the Pacific somewhere today.
Studies have shown that pieces of floating pumice can become wildlife habitat, attracting microbes, then algae. Over time, barnacle larvae, crabs, snails and worms may settle on the floating rock as well as colonies of tiny animals called bryozoans. Essentially, each piece of pumice has the potential to be a biological raft, carrying organisms to new places where they could never reach under their own movement.
- It was born from volcanoes, is millions of years old – and it’s still growing today
- "The idea was that they would inhale the spores and become infected. And they did — most died within days. The island was then burned to kill the spores"
- Mount St. Helens erupted in 1980, then a team of gophers were helicoptered in to bring it back to life
Some optimistic reports claim that the pumice might potentially bring corals with them and help restock damaged reefs. For instance, the pumice raft that occurred after an eruption near Tonga in 2019 brought material towards the Great Barrier Reef raising hopes that it would help reseed the depleted habitat. The rafts certainly provide a living 'bridge' between isolated and increasingly rare habitats.
Pumice rafts may be occasionally mistaken for real islands. In the 19th century, Sandy Island was added to maps of the Coral Sea to the west of the French territory of New Caledonia. It remained on nautical charts well into the 20th century but its disappearance was confirmed in 2012 when an Australian research vessel explored the area and found only deep sea. Some experts now believe that the origin recordings of 'Sandy Island' were really sightings of a pumice raft.
top image: Close up of grey pumice volcanic rock, Hawaii, USA. Credit: barbaraaa/ Getty Images
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