A satellite image captured a massive vapour plume in the Pacific Ocean, 1,000 kilometres north-east of New Zealand, at 1.26 am on 19 July 2012. Below the surface, a grey-brown slick began spreading across the water, marking what scientists suspect was one of the largest deep-water volcanic eruptions ever recorded. The eruption originated at the Havre Seamount, a submerged caldera sitting 500 metres or more below the sea level.
Trillions of Pumice Pieces Blanketing 400 Square Kilometres
The floating debris consisted of trillions of pumice fragments ejected from the seabed volcano, with some pieces growing as large as a basketball. Within a single day, the Havre Seamount spewed enough material to cover 400 square kilometres at a depth of 3.5 metres. Pumice forms when molten igneous rock is violently ejected under extreme pressure, cooling and depressurising rapidly to trap air inside a bubbly texture that allows the rock to float easily.
Tectonic Plates Driving the Kermadec Arc Eruptions
The Havre Seamount rises 1,000 metres from the ocean floor with a diameter of 4.5 to 5 kilometres, featuring a summit sitting 650 to 720 metres below the surface. Fresh sonar mapping revealed that a distinct cone formed inside the caldera after the 2012 eruption. The volcano lies along the Kermadec Arc, a fault line where the Pacific Plate subducts beneath the Indo-Australian Plate, dragging water and volatile compounds down to fuel continuous volcanic activity.
Shipping Hazards Across 550,000 Square Kilometres of Ocean
Wind and ocean currents broke apart the initial debris mass into smaller rafts and long ribbons that eventually spanned 550,000 square kilometres of the Pacific Ocean. These floating rock fields pose significant threats to maritime transit by damaging propellers and clogging seawater intake valves used to cool large vessels. Similar hazards emerged in 2021 when the Fukutoku-Okanoba undersea volcano, located 1,200 kilometres south of Tokyo, erupted masses of pumice that disrupted tourism, fisheries, and harbours in Japan and the Philippines, according to discoverwildlife.com.
Biological Rafts Transporting Marine Ecosystems
While most pumice slowly absorbs water and sinks to the ocean floor over time, fragments can remain afloat for years, washing ashore on northern Australia, New Zealand, and various Pacific islands. Studies show that these floating rocks act as biological rafts. Microbes and algae colonize the surfaces first, followed by barnacle larvae, snails, crabs, worms, and colonies of bryozoans that travel to distant habitats they could never reach independently.
Common Questions About Submarine Pumice Rafts
Can floating pumice really help restore damaged coral reefs?
Optimistic researchers suggest that pumice rafts could potentially restock depleted reefs by transporting material. For example, a pumice raft generated by a 2019 eruption near Tonga drifted toward the Great Barrier Reef, raising hopes that it might help reseed the threatened habitat.
How deep underwater was the Havre Seamount eruption?
The eruption occurred at a depth of 500 metres or more below the sea level, making it the largest deep-water volcanic eruption ever recorded.
Where did the drifting pumice end up?
Ocean currents spread the debris across 550,000 square kilometres of the Pacific before the material gradually waterlogged and sank, though some pieces ultimately washed ashore on northern Australia, New Zealand, and Pacific island beaches.
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