Experts may need to rethink the damage caused by New Zealand volcanoes, a University of Otago volcanology professor says (File image). Photo: AFP / Mint Images
An international study suggests New Zealand is underestimating the damage caused by volcanos.
The study, from Geophysical Research Letters, analysed ash deposits at the Ubehebe crater in California, United States.
One of the study's authors, University of Otago volcanology professor James White, said the Ubehebe crater was familiar.
"The kind of volcano that's present at Ubehebe is one that's also found in Auckland at various places," he said.
"Most of the ones that are circular lakes now."
His conclusion, was that Auckland's volcanoes were more powerful than originally thought.
In the event of an eruption, National Emergency Management Agency would evacuate everyone in a five or six-kilometre radius, but the deposits left by Ubehebe stretched almost twice as far.
"We may be underestimating [volcanoes]," White said.
"We were surprised when we started tracing out the deposits, out there in the desert, and we were still able to identify them five, or six, and then almost 10 kilometres away."
That meant an eruption in Auckland could cause significant damage, even seven or eight kilometres away.
"In places like the Auckland volcanic field, where we have a number of potential sites of eruption, we already have plans to move people five to six kilometres," he said.
"This study suggests you might want to add another few kilometres onto that."
Even over hilly or dense areas, he said volcanoes could cause serious damage several kilometres away.
White and the other researchers compared the deposits across different terrains.
"One of the directions was a pretty smooth path away from the volcano, and that's where we found the most far away deposits," he said.
"The other direction is going across some really rough topography, with hundreds of metres of relief, and the current went five or six kilometres in that direction as well, so these things aren't gonna be slowed down just by a little bit of hilly topography."
But how much can an American volcano tell us about New Zealand?
More than we could learn on our own, White said.
"There's very little vegetation and rainfall, so we're able to see things that just aren't easy to see at most volcanoes," he said.
"If you tried to do the same thing around Auckland, everything has been turned into soil since those volcanoes erupted."
Without a clear and well-preserved crater, identifying ash deposits would be almost impossible.
"The reason we think this might have been overlooked is that this is a relatively young volcano, about 2000 years, and it erupted in a very dry area with virtually no vegetation," he said.
"That's what allows us to see these relatively thin deposits, some are only a few centimetres thick, but they still represent the passage of a current that would've been dangerous to people standing in the way."
James White suggested that Civil Defence analyse the study's findings and consider updating its evacuation plan.