Scientists are firing rocks at roofs in a fascinating study exploring how buildings across Auckland might fare in an explosive eruption.
Auckland straddles a large volcanic field home to more than 50 volcanic centres, posing an ever-present hazard to the city's 1.6m-strong population and its billions of dollars of property and infrastructure.
While its existing volcanoes are thought unlikely to erupt again, the Auckland Volcanic Field is young and potentially active - with the potential to bring fast-moving surges of hot rock and gas, and widespread ashfall.
Recent studies have suggested signs of an imminent eruption could occur with anywhere between five and 15 days warning, forcing the evacuation of perhaps more than 400,000 people.
University of Canterbury researcher Professor Thomas Wilson and his team have been researching a variety of aspects of volcanic activity, simulating what may happen to buildings exposed to a future Auckland eruption.
"Our role as researchers is to put that risk in context and understand what the likely impacts are to help our partners in the public sector refine planning and decision-making around any potential future event."
That work has included PhD student Nicole Allen firing volcanic rocks at high velocity onto typical Kiwi roof designs, and also loading them with tonnes of volcanic ash.
"By testing the strength of the roofs, we can see what damage may be sustained by buildings, which in turn can help us understand how many homes could be damaged in eruptions and what we could do to protect them," she said.
"This may also help inform how much protection New Zealand buildings provide to people caught in an erupting volcano, and if they can provide a useful place to shelter."
The projects of Wilson's team are part of the ongoing Determining Volcanic Risk in Auckland (DEVORA) research programme, jointly led by the University of Auckland and GNS Science.
Wilson said funding offered by the Earthquake Commission, Auckland Council, and Auckland Emergency Management to DEVORA over the past 12 years had been "precious".
"The coming together of scientists and the public sector to help inform volcano risk management is pretty unique internationally and provides New Zealand with an amazing long-term capability to make the best decisions."
The last eruption in the area was Rangitoto around 600 years ago - considered recent in geological terms.
Unlike the big volcanoes in the central North Island, the Auckland field triggered smaller eruptions in new locations - something which had created the cones and some lakes seen around the city today.
Wilson said the chance of a volcanic eruption in Auckland was roughly between five and 15 per cent within a person's lifetime, "which is fairly unlikely in our lifetime".
"But if it did happen, the impacts would be so large that it is well worth the emphasis we are putting on the planning for potential evacuations, insurance exposure, and critical infrastructure resilience with our partners in the public sector," he said.
"A volcanic eruption could create multiple hazards, not just ashfall, but also lava flows, ballistic projectiles, hot ash and gas surges, shockwaves, landslides or even a tsunami, so it is important to build reliable impact assessment models for all possible events."
Last year, DEVORA scientists moved closer to creating a realistic picture of what types of eruptions could unfold around the city, by combining two approaches that enabled specific risks to be matched to locations.
It allowed them to more clearly see how areas north of the airport are more at risk of phreatomagmatic eruptions – not too dissimilar to that of Whakaari/White Island's deadly blow in December 2019.
The central city, meanwhile, could be exposed to mainly magmatic effects, like lava fountaining from the ground and lava flows.