Island gave few clues it was about to blow
Those on Whakaari/White Island when it erupted may not have had much warning of what was about to happen, a geologist says.
A video from tourist Allessandro Kauffmann shows conditions on White Island shortly before the crater blew on Monday.
Kauffmann was back on his tour boat by the time it happened, but had been filming at the crater during his visit.
Smoke plumes and streams changed colour, prompting a guide to say he was a ‘‘little bit worried about why it’s going green’’.
University of Auckland associate professor in geology Phil Shane watched the video yesterday.
‘‘Probably the interesting thing about the video, it just shows that – leading right up to the eruption – there wasn’t really any indication that there would be an explosion of that size,’’ he said.
Signs such as bubbling or steaming could be what visitors were expecting to see on Whakaari, and the eruption was relatively small, despite its effects.
‘‘It’s only because people were right in there that we’re even discussing this,’’ he said.
‘‘Anything’s catastrophic if you’re standing right on the spot.’’
University of Auckland vulcanologist Professor Shane Cronin said he’d been on the island when ‘‘it has been much more vigorously steaming than that video’’.
Cronin spotted potential signs of unrest in Kauffmann’s video, but eruptions are hard to predict.
‘‘You never get, oh, this is happening so you’re going to get an eruption.
‘‘You never get a straight line between one thing and another,’’ he said. Instead, with volcanoes, it’s about learning from experience – looking at what happened before past eruptions and working out what were normal changes and what were significant.
‘‘That’s what everyone will be trying to do over the next little while.’’
After watching videos of the eruption, Cronin picked some possible warnings that the volcano was heating up.
Several individual pulses of steam from the crater lake could have been escaping from a pressurised area or indicating more heat coming into the system.
The stream appears to have got a bit hotter, Cronin said, causing a colour change when it interacted with the surface below.
‘‘Those little surface changes, they do happen all the time. And not all of them link directly to anything more dramatic like an eruption.’’
Once the eruption began, much of the energy went sideways, Cronin said.
‘‘There are ash particles, fine particles of rock and coarse particles of rock all radiating outwards, like an explosion blast.’’
Black areas of the cloud were where water vapour hadn’t cooled on meeting the air, he said, and it turned white once it did.
Blocks of rock also fell, leaving white steam trails as they cooled while travelling through the air.
It’s thought the eruption was due to a buildup of pressure at a shallow depth, Shane said, which was hard to detect.