Auckland’s volcanoes have released vast amounts of toxic gas in past eruptions, with new research filling a "critical" gap in the city’s emergency planning.
Funded by the Natural Hazards Commission Toka Tū Ake and Auckland Council, the study is the first to estimate gas emissions from the Auckland Volcanic Field.
It found that over the past 200,000 years, Auckland’s volcanoes have released about 26,000 kilotonnes of carbon dioxide and 9000 kilotonnes of sulphur dioxide.
The youngest and largest eruption – forming Rangitoto Island – released enough gas to fill roughly 3.5 million hot air balloons, according to the study’s lead author Elaine Smid from the University of Auckland.
Auckland’s volcanoes have let loose about 26,000 kilotonnes of carbon dioxide over the past 200,000 years. (Source: 1News)
The likelihood of an eruption remains low – estimated at about 10% over the next 50 years.
"Gas is a significant but under-recognised hazard in Auckland," Smid said. "But we didn’t have the numbers because this is quite difficult data to get."
As Auckland hasn’t erupted in modern times, researchers analysed ash and rock from five past eruptions, including Rangitoto.
They estimated gas release by comparing gases trapped in magma crystals to that in rapidly cooled volcanic glass.
Volcanic gas could pose serious health risks, particularly in a densely populated city such as Auckland.
“There’s a few reasons to be concerned about volcanic gas,” Natural Hazards Commission chief resilience officer Jo Horrocks told 1News. “The first one is mainly for human health, particularly for people with respiratory illnesses like asthma.”
She said gas concentrations during an eruption would be far higher than those experienced in places such as Rotorua.
Gas – particularly sulphur dioxide – could also damage buildings and infrastructure.
"It can be very, very corrosive," Horrocks said.
While scientists now had a clearer picture of how much gas could be released, key uncertainties remained.
“The same amount of gas erupted in four days will be quite different in terms of hazard than that same amount of gas erupted over 300 days,” Smid said.
“That’s where eruption duration really plays a big part.”
Another major unknown was whether gas release could provide early warning of an eruption.
Auckland’s volcanic system was unusual because eruptions were expected to occur in new locations.
“One of the biggest features of the Auckland volcanic field is that we don’t know exactly where the next eruption will be,” Horrocks said.
Smid added: “We’ve got 1.8 million people living on top of a potentially active volcanic field.
“That’s why it’s so important to study.”
Auckland Council said it continued to support research to better understand volcanic risks in Tāmaki Makaurau.
“We are following the development of this novel research with interest and will look at how and if it can be incorporated into emergency plans at the appropriate time,” principal science advisor for Auckland Emergency Management Dr Angela Doherty said in a statement.
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