Pumice

I had just given a lecture to the expeditioners about the geological evolution and formation of the Kermadec region and why the volcanic Raoul Island exists - when there was a commotion on the bridge and we were changing course to go and check an expanse of white/cream on the ocean surface, up to 250 km long and 100 km wide, that had been spotted by a maritime surveillance plane flying back from Tonga. The Captain Sean Stewart called me over to ask me what I thought it might be? "Well it is unlikely to be an ice-berg this far north - most likely it is pumice from a volcanic eruption." He was a little reticent about approaching it as it might do damage to the ship, but we set off to see if we could intercept it.

A few hours later we started to spot the first few pieces of pumice floating by (we were actually trying to spot whales and dolphins at the time as we were still quite a way from the original sighting by the aircraft). The concentration of pumice started to increase over the next few hours and we used some high tech ropes and buckets to try to catch pieces as they floated by. The pumice pieces ranged in size from marbles to soccer balls. Unfortunately the wake pushed the pieces out from the side of the ship, making it rather hard to catch them. It became quite competitive between the guys with the buckets.... after about 30 minutes we had collected just 30 pieces of pumice and the largest one the size of a tennis ball.

The captain and the buffer with the largest piece of pumice

We continued to see pumice streaks for the rest of the afternoon, but assumed that the wind and waves had dispersed the original expanse seen on the photos. However at midnight the ship hit a large concentration of pumice, 1 m deep and stretching as far as the spotlights could see, although only 600 m wide. Unfortunately they didn't take any photos or collect any samples, or wake me up, but they did take down the position. Th officer of the watch Lt Tim Oscar described it as "the weirdest thing I have seen in the 18 years I have spent at sea." However, I did get some samples as it turns out that some pumice got sucked up into the water intake system that cools the engine and they were cleaning out their filters the next day and gave me some of it.

Science writer Rebecca Priestley was writing a daily blog for the expedition and as an ex-geologist she decided to cover the pumice story. The navy also decided to put some photos up on their website and reposted her blog - for some reason the media jumped on the story and it was reported all over the world. It must have been a slow news day! Several other organisations jumped on the band wagon with their own interpretation and information. The satellite images from NASA show that the pumice was first seen on the 19th July and that its most likely source is Harve volcano. We originally thought it might be Monowai as we  knew there was ongoing seismic activity there, but it was a lot further north. I have given the pumice samples to a student at Victoria University in Wellington that is studying this region and working on pumice to analyse. The chemical fingerprint of the pumice will help us to determine which volcano they are from. Hopefully we will know in a couple of weeks - watch this space.

The streaks of pumice intercepted again on the way back from Raoul

So I became a vulcanologist for the trip - there was supposed to be a vulcanologist from GNS Science on the voyage up to Raoul, but he had pulled out at the last minute due to the eruption of Tongariro in the north island the day before we left. You just can't escape geology in New Zealand.