Mt Ruapehu's eruption in 1996. Scientists estimate they're aware only of 10 per cent of the eruptions that have taken place in the Taupo Volcanic Zone's 1.6 million year history. Photo / File
Mt Ruapehu's eruption in 1996. Scientists estimate they're aware only of 10 per cent of the eruptions that have taken place in the Taupo Volcanic Zone's 1.6 million year history. Photo / File
The volcanic heart of the North Island has unleashed some of the most devastating eruptions on the planet over the 1.6 million years it's been active.
The last major eruption from Lake Taupo, nearly 1800 years ago, belched more than 30 cubic km of material into the atmosphere.
Yet this was little compared with the monster blow that largely created the lake itself.
The Oruanui eruption, which happened about 26,500 years ago, was also the world's most recent "super-eruption" and topped the Volcanic Explosivity Index.
Despite its fiery past, the swathe of New Zealand we know as the Taupo Volcanic Zone (TVZ) remains surprisingly sparsely understood.
Our current knowledge was skewed toward the past 61,000 years – a period generally well preserved by the geologic record – but more than 90 per cent of picture was still missing.
And what we did know was largely based around those bigger blows, while the evidence of smaller or older events had been buried or destroyed over hundreds of thousands of years.
Dr Jenni Hopkins, of Victoria University's School of Geography, Environment and Earth Sciences, suspected we'd significantly under-estimated both the frequency of eruptions on the TVZ, and what threat they posed in the future.
"Impact assessments suggest that a future eruption from this area, would likely cause disruption to aviation, and be catastrophic for critical infrastructure that supports two of New Zealand's largest industries: agriculture and tourism."
Hopkins and fellow researchers are now trying to fill in these blank spaces, using recovered traces of volcanic ash that were long hidden within ancient seabed sediments, about 200km east of New Zealand.
Because they'd been relatively well preserved in comparison to their on-land counterparts, they offered a finer – and likely complete – record of what had unfolded over more than two million years.
Part of their focus would be on something called macroscopic tephra, or visible deposits preserving past voluminous eruptions, however Hopkins said, "a growing number of studies internationally have shown that the smaller eruptions are often preserved as microscopic material known as cryptotephra."
"Cryptotephra studies are rapidly becoming the premier technique for generating comprehensive records of volcanic activity preserved in the geologic record."
They'll use state-of-the art core scanning technology to analyse the deposits, before eventually teasing out and then reconstructing eruptions from the past.
But by their very nature, cryptotephra are invisible to the naked eye, so researching a method to identify them would be a challenge in itself.
"In addition, the sheer number of potential samples and data we will be dealing with will cause some head-scratching, I'm sure."
Their final goal would be to work out the intervals between each event, which they'd do by combining geochemical and geophysical data.
The ultimate findings of the study, supported with a $300,000 grant from the Marsden Fund, would be fed into risk planning, Hopkins said.
"With the data telling us the frequency, size, dispersal, componentry and geochemical composition of the eruptions, these are all important aspects which can provide insight into the characteristics of a future eruption from the TVZ."
Inside deadly pyroclastic flows
Meanwhile, another Kiwi scientist has been modelling one of the most deadly and devastating effects of a volcanic eruption: pyroclastic flows.
These hot, fast-moving currents of ash and gas rush down the sides of volcanoes and have featured in some of the world's biggest recent blows – notably the 1980 eruption of Mt St Helens in the United States, which left 57 people dead.
A more recent occurrence was during the catastrophic eruption of Fuego Volcano in Guatemala this year, affecting more than 1.7 million people, and leaving hundreds dead or missing.
Massey University researcher Ermanno Brosch on the summit of Italy's Stromboli volcano. Photo / Supplied
Massey University PhD student Ermanno Brosch has been researching a dilute type called pyroclastic surges, which were less concentrated in particles and have a lower density compared to pyroclastic flows.
"These surges – as we call them in short - are very hot, very fast and very powerful and they can cause massive destruction during explosive volcanic eruptions," Brosch said.
"Also, being less concentrated than pyroclastic flows, they have an increased flow mobility which makes it harder to predict their flow path."
Predicting how they would behave and propagate was vital in protecting future settlements and people from these flows, he said, but the problem was that so little was known about what occurred inside them.
"No one had a direct look inside these flows during eruptions in order to understand how they are made up internally, for obvious reasons - real world flows are too dangerous to investigate directly."
But an eruption simulator at Massey, dubbed the Pyroclastic flow Eruption Large-scale Experiment, or PELE, has been yielding some insights.
PELE was an experimental set-up able to generate these flows as they occurred in nature - but in a small scale.
This allowed scientists to explore the internal mechanisms that drove the flows.
In his work, Brosch has conducted some large-scale experiments that required months of preparation and a large number of sensors and cameras.
So far, he'd been able to reveal a range of mechanisms that generated the flows' destructive potential.
His next goal was to reproduce these experiments using complex numerical models.
"The results of my study will be useful to research as they will increase the knowledge we have about these flows," he said.
"For instance, to understand how their destructive power is generated.
"With my research I hope that advanced models can be created for hazard assessment to predict the impact of pyroclastic surges and to identify high risk zones around volcanoes."
