New Zealand scientists have described the destructive eruption of a Hawaiian volcano an "eerie analogue" of what could happen in Auckland.
Now, as molten lava from Kīlauea volcano continues its devastating spread across Hawaii's Big Island, a researcher is investigating what might happen to underground water pipes and power cables in an Auckland scenario.
Although the long-dormant Auckland Volcanic Field (AVF), doesn't have active shield volcanoes like Hawaii's Kīlauea, the city could still get an eruption that generates lava fountaining and lava flows from fissures.
Sophia Tsang, an EQC-funded student researcher at University of Auckland, carried out tests at the end of last year at Syracuse University's Lava Project in the US and is in the final stages of learning what disruptions underground flows could have in our biggest city.
The experiments allowed Tsang access to a furnace that heated rocks to 1300C above the melting point of basalt - which was just the type of rock that Auckland's volcanoes produced.
"I used basalt to make pāhoehoe lava flows, one of the types of lava flows that we are likely to get in Auckland, and tested it over Auckland-type soil, asphalt roads and concrete footpaths – which are where a lot of our infrastructure is buried."
To measure the heat effect, Tsang and the team buried temperature probes in the ground at various depths, before pouring lava of different thicknesses over the area.
"It was really exciting being so up close with lava," she said.
"I've been to Hawaii and seen natural lava flows in the field, but what you don't commonly see in the field, is how the ground actually reacts under the lava."
Her team had so far found that at one metre thick, the Auckland-type lava barely affected the ground past 40cm deep.
"But of course, if we get an eruption in Auckland, the lava flow could be a lot thicker and flow for longer than in my experiment," she said.
"I've taken my results from the Lava Project to begin estimating temperatures under larger lava flows, which will allow researchers and companies that provide essential services to assess how a lava flow could impact Auckland's underground pipes and cables."
Her preliminary results suggest that Auckland's key infrastructure was likely buried deeply enough that it would not be impacted during a short eruption. However, the length of time the lava flows could change that.
"The length of time the lava flow is active strongly controls how much heat is transferred into the ground below."
EQC research manager Richard Smith said the new research will be a great addition to research on reducing the impact of a volcanic eruption on Auckland.
"Communities rely on infrastructure to keep functioning after a natural disaster," he said.
"Even if your house is undamaged, you will only be able to stay there if you have services like water, sewerage and power.
"Research like Sophia's helps understand what could happen to infrastructure in a volcanic eruption now, and also help planners working on future projects avoid these kinds of hazards."
Tsang said damage to pipes and cables was certainly something other places, such as Hawaii, had been concerned about during eruptions, as underground pipes and cables could heat up, potentially meaning limited water, sewerage and power service to parts of a city.
"In 2014 Department of Water engineers in Hawaii had to locate and install valves to minimise the number of customers affected by a lava flow and we're keeping a close eye on what happens to water supply during the current Kīlauea eruption."
Now that Sophia has gathered temperature data from under mini lava flows and created a model to estimate the heat transfer from lava flows into the soil below, her research would focus on determining where lava would flow in a series of eruptive scenarios developed by the Determining Volcanic Risk in Auckland (DEVORA) research programme.
Tsang would then take her work from the Lava Project to investigate potential impacts to buried infrastructure for the scenarios she models.
"These results will help planners and infrastructure providers reduce the risk of water, sewerage and power failing across a wide area if there is a lava flow," she said.
"And with Auckland built on 53 volcanoes, it's something we need to think about."
Sarah Sinclair, acting director of Auckland Emergency Management, said the research would be used to help with emergency planning.
"Knowing how our city and its infrastructure would cope in the aftermath of a volcanic eruption is critical," Sinclair said.
"This kind of information is helping us to plan and build resilience and it's important that we all think about these things.
"While it might seem daunting, planning for a volcanic eruption is no different to planning for any other disaster – have a talk with your loved ones and make a plan."
The closest Auckland has to the type of activity on Hawaii is Rangitoto, which is sometimes referred to as a miniature shield volcano.
While the AVF's volcanoes have each erupted for a short period of time, with long gaps between each volcano forming, the time between eruptions had been highly variable - and it was unlikely that someone would experience an eruption in Auckland within their lifetime.
Another difference between the AVF and Hawaii's experience was that activity on Kīlauea was mainly effusive - gentle extrusion of lava spatter and lava flows - but abundant groundwater and seawater in Auckland meant the city could also get violent explosive eruptions when magma encountered water.
Past eruptions in the local field had typically started with an explosive phase that generated fast-moving clouds of ash, gases and debris away from the vent and excavated a crater.
Some eruptions had then stopped but others continued in a gentler, more effusive manner after the magma stopped interacting with water, leading to the development of scoria cones.
The eruption on Kilauea was preceded by several days of warning signals including earthquakes, which Aucklanders could also expect before a big blow.
A better understanding of how a future eruption might affect Auckland - including how many people might need to be evacuated and how hazards such as lava flows and ash might have an impact - was one of DEVORA's aims.
Previous research has estimated a catastrophic volcanic eruption in Auckland's industrial heart could have an economic impact of up to $10 billion in the first year and knock out a large chunk of the city's GDP.
Much of Auckland was at risk - the AVF stretched across 360sq km and more than one million people live on areas where an eruption could occur - but it was in the core industrial hotspots of Penrose, Onehunga, Otahuhu and East Tamaki where such a disaster would be most damaging to Auckland's economy.
In 2015, researchers estimated such an event could cost on average $8.3 billion (in 2007 dollar terms) in lost GDP from businesses, factories and supply chains being taken out.