A simulation of a volcanic eruption in the Auckland area. Video / Brandspank
Auckland’s next major volcanic eruption could throw concentrated sulphur dioxide across hundreds of square kilometres – threatening the health of the city.
That’s according to a new study simulating the impact volcanic gases could cause in an extreme eruption scenario.
While its 53 volcanoes are considered unlikely to erupt again, the Auckland Volcanic Field (AVF) is young, potentially active, and could produce fast-moving surges of hot rock and gas, lava bombs and widespread ashfall.
Recent research has suggested Auckland will receive between five and 15 days’ warning of an imminent eruption , forcing the evacuation of perhaps more than 400,000 people from their homes.
Until now however, the potential health risk of sulphur dioxide (SO2) from rising magma has been less understood.
“Volcanic gases have always been considered a very likely hazard during future AVF eruptions, but no one had done any quantitative studies to assess how severe the impacts could be,” said study co-author Elaine Smid of the University of Auckland.
SO2 is a fast-acting breathing irritant known to cause coughing and chest tightness, dizziness and shortness of breath. It could be especially hazardous to older people, children or those with existing health conditions.
Although volcanic gases typically don’t cause big hazards in eruptions - Auckland is a special case.
“Around the world, it is fairly rare for people to live directly on - or beside - the eruption vent, where gases will be most concentrated before, during and after an eruption,” said study co-author Professor Tom Wilson of the University of Canterbury.
“In the case of Auckland City, the scientific evidence indicates that a future eruption will occur within the city and the AVF is likely to emit large volumes of gas - and exposure to volcanic gases will likely be quite high, so we can expect impacts.”
Auckland lies sprawled across a young and potentially active volcanic field.
The study team modelled a scenario involving an eruption near Māngere Bridge, producing high flows of volcanic gases.
They then assessed how gas concentrations would disperse over different time periods.
Study lead author Siena Brody-Heine, also of the University of Canterbury, said the modelling indicated large parts of Auckland would be exposed to ground-level gas concentrations exceeding thresholds for health.
“The competing sea breezes from the Waitematā and Manukau Harbours, the location of the eruption, weather, and time of day will have a significant influence on the gas dispersion patterns and which areas of Auckland would be most affected.”
Fellow author Associate Professor Carol Stewart of Massey University, said the results suggested hundreds of square kilometres could be exposed to high concentrations for hours - or even days.
The modelled scenario could see asthma-related cases double at hospital emergency departments, she said, and close to a new vent, SO2 concentrations could be life-threatening.
“The establishment of an evacuation zone around the vent should mitigate the life safety hazard, but monitoring of SO2 concentrations will be necessary to inform the management approach.”
Wilson said while the study was focused on health implications, the gas levels could also have damaging effects on critical infrastructure and buildings in the city.
Having looked at the worst-case scenario, the team now plans to model a wider range of weather conditions.
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
