Deathly clouds of hot, fast-moving gas and debris could travel much farther than previously thought in a volcanic eruption in Auckland, according to new research.

The current estimate of how far deathly clouds, known as base surges, can travel is far too conservative, based on international research, says Gemechu Teferi, who is researching volcanic risk in Auckland.

Base surges are one of Auckland’s most deadly volcanic hazards. They form when magma mixes with groundwater, creating a low-lying cloud of volcanic gas, ash, and rock that can move at tens of metres per second.

Scientists are working to revise estimates of base surges to better plan for future events as part of a programme funded by the National Hazards Commission Toka Tu Ake, and Auckland Council.

Research into Ubehebe Craters in California’s Death Valley, a volcanic zone similar to the one found beneath Auckland, has found evidence of base surges 10 to 15 km from volcanic vents.

“This is at least two times farther than previous estimates of how far surges can travel, and we want to know if such distances are also possible in the Auckland Volcanic Field,” said Teferi, who is leading the research with the programme as part of his PhD.

The arid environment in Death Valley is excellent at preserving geological evidence that would otherwise be eroded by weather, vegetation, and urban development in places like Auckland.

Auckland Emergency Management’s response plan for a future eruption in the Auckland Volcanic Field has been updated to include the longer surge run-out distances. Still, studies are needed to test whether these can be realistically expected in Auckland.

Natural Hazards Commission resilience officer Dr Jo Horricks said the research has implications for planning for future eruptions.

“If confirmed, it means the impacts of a volcanic eruption in Auckland would be potentially far greater than we previously thought,” the volcanologist said.

At least 42 of Auckland’s 53 volcanoes show evidence of phreatomagmatic eruptions, which are known to involve base surges.

Teferi has visited over 30 of these sites and selected nine which showed the best geologic evidence of base surges for further investigation.

In the coming months, Teferi’s team will analyse rocks from the selected sites using a technique known as AMS (Anisotropy Magnetic Susceptibility), which can pick up microscopic evidence of the flow behaviour of past base surges.

Teferi will feed the geological evidence and AMS analysis into a computer model that will estimate the true distance the base surge travelled. He will then simulate possible future base surge scenarios.

The information will support councils, emergency responders, and loss modellers with planning for the impact of future eruptions.

Said Horrocks: “Although unlikely, the impact of a volcanic eruption on Auckland is huge and base surges will be one of the biggest hazards. A more accurate estimate of how far these deadly clouds will travel can help councils with evacuation planning and insurers with estimating potential losses.”