Raft of pumice floats off New Zealand
Published: 6:04PM Friday August 10, 2012 Source: ONE News
A navy ship sailing towards the Kermadec Islands has encountered a 25,000 square kilometre area of pumice pieces.
The area of floating pumice was estimated to be 250 nautical miles in length and 30 nautical miles wide.
The Royal New Zealand Air Force (RNZAF) Orion spotted the phenomenon yesterday afternoon, while on maritime patrol from Samoa to New Zealand.
The area of floating pumice is about 85 nautical miles off West South-West of Raoul Island.
Lieutenant Tim Oscar, a Royal Australian Navy officer described the phenomenon as “the weirdest thing I’ve seen in 18 years at sea”.
He said the raft of pumice was moving up and down with the swell as far ahead as he could observe.
“The rock looked to be sitting two feet above the surface of the waves, and lit up a brilliant white colour in the spotlight. It looked exactly like the edge of an ice shelf,” said Oscar.
RNZAF staff had been briefed by GNS Volcanologist Helen Bostock the previous day when the ship first encountered an area of pumice from an undersea volcano, believed to be New Zealand’s third erupting volcano - the undersea Mount Monowai.
“I knew the pumice was lightweight and posed no danger to the ship. None-the-less it was quite daunting to be moving toward it at 14 knots.
“It took about 3 – 4 minutes to travel through the raft of pumice and as predicted there was no damage. As we moved through the raft of pumice we used the spotlights to try and find the edge – but it extended as far as we could see,” said Oscar.
The Commanding Officer, Commander Sean Stewart changed course to intercept the pumice, and brought the ship to a halt to enable retrieval of samples.
The samples will be analysed to determine which volcano they came from.
Monowai, 3rd volcano thought to have erupted
(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.
Monowai seamount, also known as Orion seamount, rises to within 100 m of the sea surface about halfway between the Kermadec and Tonga island groups. The volcano lies at the southern end of the Tonga Ridge and is slightly offset from the Kermadec volcanoes. Small parasitic cones occur on the north and west flanks of the basaltic submarine volcano, which rises from a depth of about 1500 m and was named for one of the New Zealand Navy bathymetric survey ships that documented its morphology. A large 8.5 x 11 km wide submarine caldera with a depth of more than 1500 m lies to the NNE. Numerous eruptions from Monowai have been detected from submarine acoustic signals since it was first recognized as a volcano in 1977. A shoal that had been reported in 1944 may have been a pumice raft or water disturbance due to degassing. Surface observations have included water discoloration, vigorous gas bubbling, and areas of upwelling water, sometimes accompanied by rumbling noises.
|Subregion Name:||Kermadec Islands|
|Volcano Type:||Submarine volcano|
|Last Known Eruption:||2008|
|Summit Elevation:||-132 m||- 433 feet|
Additional information on the Monowai Seamount – index of monthly reports – may be found at: http://www.volcano.si.edu/world/volcano.cfm?vnum=0402-05-&volpage=var
Presumed Floating Pumice
Tonga, SW Pacific Ocean
This report presents a serendipitous observation near Tofua, possibly indicative of volcanism elsewhere (not on Tofua). A photo of Tofua and vicinity from space taken on 13 April 2011 displays significant material on the sea surface – the possible relict of an eruption at some unknown center.
A photo taken from space by Astronaut Paulo Nespoli (figure 25) could suggest an eruption in the Southern Pacific region at an unknown volcano. Nespoli took the photo from the International Space Station on 13 April 2011 (Nespoli, 2011). It shows occasional white clouds over the island’s high points, and a thin gray-blue plume indicative of Tofua’s volcanic emissions wafting to the SE.
The elongate and sinuous bands of debris seen in the photo are suggestive of floating pumice seen before in the region (eg., see Home Reef, BGVN 31:09; 31:10; 31:12; 32:04; 33:05; 33:12; Metis Shoal, BGVN 20:06). If this is pumice in elongate strands such as seen from Home Reef’s 2006 eruption, it could also be derived from deposits of an older eruption. Debris floating in strands are most conspicuous at upper left of figure 25, where they form a curve cut by the photograph’s left edge. Faintly linked to that area is a thinner strand of sinuous debris. Other strands of similar width appear elsewhere.
Reference. Nespoli, P., 2011, Tofua Island, Tonga: Flickr (uploaded 18 April 2011) (URL: http://www.flickr.com/photos/magisstra/5618223635/).
The calculation of square area is determined by multiplying length x width. The area in the story was 250 x 30 = 7500. And 7500 square nautical miles is equivalent to 8630.8 square miles. That’s a far cry from the “nearly 10,000 square miles” cited by CNN. As a matter of fact, it’s almost the size of New Hampshire, which has 8,968.10 square miles. Or, if you prefer, it’s nearly as large as Rhode Island, Delaware and Connecticut combined (which is 7843.29 square miles.)
As well, the sailor cited by CNN in the sentence “Described by one sailor who witnessed it as “the weirdest thing I’ve seen in 18 years at sea…”" was not merely a sailor, but rather was Lieutenant Tim Oscar, a Royal Australian Navy officer.