25,000 sq km sea of pumice floats off New Zealand
(By MICHAEL FIELD AND STACEY KIRK, Stuff.co.nz)
A navy ship heading to the Kermadec Islands has sailed into a huge 25,000 square kilometre area of pumice pieces north of Auckland.
It is believed to be from New Zealand’s third erupting volcano – the undersea mount Monowai. In the past week both Mt Tongariro and White Island have erupted.
The navy said the raft – 463 kilometres by 55 kilometres – was spotted by an RNZAF Orion returning on patrol from Samoa.
Canterbury, which left Auckland on Wednesday, sailed to the raft to pick up a sample.
GNS scientists are aboard the ship, which is also carrying 30 high school students on a Sir Peter Blake fellowship to Raoul Island.
GNS vulcanologist Craig Miller said they were aware of the ”pumice raft” but did not know the exact dimensions of it.
He said it was difficult to guess how big the pumice raft could be, but the air force had flown over and assessed its size.
“We’ve been in contact with the air force recently about it. But it is floating more than 1000 kilometres offshore, so it’s a while away.”
Miller said the pumice raft was about “half way to Tonga”, and just past Raoul Island.
A science writer on the voyage to the Kermadecs has been keeping a journal of findings from each day.
Rebecca Priestley said it was “an event” which caused the Canterbury’s Commanding Officer, Commander Sean Stewart to give the order to change course.
“Up to 250 nautical miles long by 30 nautical miles wide, it stood out against the blue-grey of the ocean as a great white froth on the surface of the sea,” Priestley wrote.
She said they came across it about midday yesterday.
Navy ratings reportedly lowered buckets, tied to a rope, off the gun deck and down into the water to collect deposits, which Marine Geologist Helen Bostock, who is also on the voyage, would take back to Niwa to examine, Priestly said.
Monowai is a volcanic seamount to the north of New Zealand. It is one of the most active volcanoes in the Kermadec volcanic arc.
The most recent eruptions were in 2008 and 2011.
The summit is approximately 132 metres (433 ft) below sea level, considerably above the level of the nearby Tonga and Kermadec Trenches. The summit’s position and depth changed between 1998 and 2004, due to a landslide and eruptive regrowth. A 1500 metre deep caldera, 13 by 8 km, lies 5–15 km NNE of the seamount’s main cone.