A surprise encounter while sailing to the Kermadecs Islandsby Toby Manhire
From aboard the HMNZS Canterbury, Rebecca Priestley observes the raft of pumice, thought to be the result of an underwater explosion.
Friday August 9
“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.
Raoul Island is a pest-free nature reserve, its steep cliffs home to more than six million breeding seabirds. Like all the Kermadec Islands, the waters up to 12 nautical miles around the island are a no-take marine reserve, part of a stunning and pristine marine environment with a unique mix of tropical, sub-tropical and temperate species of fish. This is a rare ecosystem, where large predators rule, untroubled by fishing lines or nets.
On the island, New Zealand’s northernmost scientific field base is managed by a small group of Department of Conservation staff and volunteers, and that’s partly what this voyage is about.
In any given year, the Island would typically receive about 20 visitors, but this year is a bit special. As well as the annual Department of Conservation staff changeover and resupply, the HMNZS Canterbury – a big, grey beast of a ship that looks as much like a windowless building as an ocean-going vessel – is taking meteorologists, geologists, marine biologists and a large group of students on a Sir
Peter Blake Trust Expedition. We’ll spend about six days anchored beside the island. The crew and marine specialists will remain on the ship, but 50 of us will go ashore.
Rough seas are forecast. The best thing to avoid seasickness, I’m told, is a lemon and ginger tea and some fresh air. So I’m going up on deck to breath some salty air and keep a lookout for migrating whales.
I’ll let you know what we see.
Saturday August 10
I went outside at first light and found the ship in the middle of a heaving grey sea, with nothing but ocean and sky in every direction. Three dark-winged birds – probably petrels – swooped and dived amongst the waves. It might
look like a great big nothingness, but there’s a lot going on in the ocean beneath us. The birds are diving for fish or small squid. There are whales migrating south as we sail north. There are volcanoes in the depths beneath us, their slopes and geothermal vents home to a rich and often bizarre diversity of flora and fauna.
Then, 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.
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 [National Institute of Water and Atmospheric Research] 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.
While we were outside pumice spotting we saw more petrels and an Antipodean albatross. And then, at last, a whale! Not a humpback, which are known to follow this path on the annual migration from the tropics to their Antarctic feeding grounds, but a minke whale.
We’re now sailing at about 17 knots, and should reach Raoul Island overnight. We’re all hoping for calmer seas.
Dr Rebecca Priestley is travelling on the HMNZS Canterbury as part of a Sir Peter Blake Trust voyage to the Kermadecs. The above entries are cross-posted from the American Scientist website, where Rebecca is blogging her trip to the Kermadecs.
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