Kermadecs voyage #2: The mystery of the floating pumice

I was planning to write this personal blog at the same time as writing one for Scientific American, but I’m so busy circumnavigating islands in a RHIB, flying into volcanic craters in a Navy Seasprite, fishing for sharks off the back of the HMNZS Canterbury and helping rescue Kermadec storm petrels (it’s my job!) that I haven’t found the time. You can read my Scientific American blog posts but by all the media calls coming into the ship about the pumice raft we encountered a couple of days ago, I’m guessing that there might be a bit of interest in it (I have no internet connection here, just the ability to send out pre-arranged emails using a New Zealand military email addresses).

Just to summarise, here’s the story of the pumice, as I’ve posted on Scientific American’s expedition blog:

Wednesday 8 August 2012

“You can’t escape the geology in New Zealand,” said Helen Bostock, a marine geologist on the voyage. “It’s in your face whether you like it or not.”

It’s true. As we left Auckland this morning we were sailing away from two erupting volcanoes: Tongariro, in the middle of the Taupo Volcanic Zone, had just erupted for the first time in more than 100 years, depositing ash around the central North Island. White Island, a busy little volcano in the middle of the Bay of Plenty, was erupting ash from its Crater Lake.

So where are we heading? We’re sailing north along a chain of underwater volcanoes to another active volcano, Raoul Island, about two days sailing from Auckland. Raoul Island – the top 516 meters of a submerged volcano whose slopes extend for thousands of meters beneath the ocean – last erupted in 2006 and we hope it will stay quiet for our visit.

Thursday 9 August 2012: 

… at midday, our Commanding Officer, Commander Sean Stewart, gave the order to change course. A marine patrol aircraft, flying from Samoa to New Zealand, had spotted “an event” in the ocean north of us. 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.

Marine geologist Helen Bostock said the deposit could be a mixture of ash and pumice from an underwater volcanic eruption. There was only one way to find out – sample it. By the time we reached the deposit, the ash had dispersed, but blocks of pumice were bobbing past us in the water.

Commanding Officer Sean Stewart and Chief Petty Officer Henry Matangi with a big piece of pumice collected by Matangi. Photo by Helen Bostock.

Sometimes science is about using whatever tools you can find when faced with a serendipitous opportunity. At Helen’s request, a couple of young Navy ratings lowered buckets, tied to a rope, off the gun deck and down into the water. There was a big cheer when they came up with a few small pieces of pumice – brand-new, freshly-minted rock – in the bucket.

But from where? We have some people on board from Geonet, whose role is to monitor seismic and volcanic activity around New Zealand. They say that Monowai, an undersea volcano north of Raoul Island, has been showing activity for the past five days. Helen says that when she gets the pumice back to her NIWA laboratory, they will do a chemical analysis. “It’s like genetic fingerprinting,” she says. “Each volcano has it’s own chemical signature”. If this pumice matches Monowai, or one of the other existing volcanoes, that’s where it’s from. If it doesn’t match anything, it could be from a new volcano.

Friday 10th August 2012

Last night, when Lieutenant Tim Oscar, the Officer of the Watch, arrived at the bridge for his midnight to 4am watch (seriously, that’s what they do, all the lights on the bridge are turned off and they watch the sea) he noticed something strange. He turned the ship’s spotlights on and discovered the ship was ploughing through the wall of pumice we were looking for yesterday. The ship travelled through it for half a nautical mile, and he estimates it was two feet thick and extended sideways as far as the eye could see. “It was like being an ice-breaker hitting an ice shelf,” he said this morning. He described it as “the weirdest thing I’ve seen in 18 years at sea.”

It was too dark and the ship was going too fast to stop and take samples, so he noted down the latitude and longitude (29 59.43 degrees south and 179 25.598 degrees west) and motored on through it.

Saturday 11th August 2012

Helen Bostock with a handful of pumice collected off the side of the HMNZS Canterbury.

The engineering crew checked the ship’s water filters yesterday and, along with the usual mess of leaves and seaweed, they found a lot of small pieces of pumice. These filters, which suck in water to cool the ship’s engine, are about 10 feet below the sea surface, so when the ship went through the pumice raft on Thursday night it sucked up a lot of pumice with its water. Today, they’re giving the water filters a thorough clean. Helen Bostock has a new collection of pumice to take back to her lab in Wellington and I have a couple of small souvenirs to take home.

I’m transferring to Raoul Island tomorrow. If the weather packs in, as predicted, I’ll have time to write some more.

About Rebecca Priestley

I have a PhD in the history & philosophy of science and I write about science and science history. I live in New Zealand.
This entry was posted in Kermadecs, Science, Travel and tagged , , , , . Bookmark the permalink.

5 Responses to Kermadecs voyage #2: The mystery of the floating pumice

  1. Pingback: La erupción del monte submarino Havre del 18 de julio de 2012 « malcolmallison

  2. Pingback: Floating rocks in the ocean lead to an undersea eruption… seen from space! | Bad Astronomy | BizNax

  3. Pingback: Floating rocks in the ocean lead to an undersea eruption… seen from space! | Bad Astronomy | Discover Magazine

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  5. Pingback: Floating rocks in the ocean lead to an undersea eruption… seen from space! | Space Travels - Space Turism

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