If the Taupō already has another super eruption, and that happens on a calm day, most of the North Island will be under at least one meter of ash, suggests a new model. Researchers emphasize the likelihood of such an event being "extremely low."
On the other hand, if the eruption is much smaller and more likely, and happens on a day with a cold wind, the ashes appear to be restricted to a relatively narrow corridor that stretches over Napier. In this scenario, most affected places should receive 10mm or less of ash.
Taupō is another of the geological dragons that sleep under the New Zealand landscape. As part of an EQC research grant to gain a better understanding of Taupō's gray hazards, the researchers modeled 5000 ash eruption scenarios.
For the smallest size of eruption modeled, only the major cities on the north east island between Tauranga and Hastings were found to have a risk of over 1mm of ashfall.
CONSULT MORE INFORMATION:
* Swarm of hundreds of small earthquakes near Taupo
* The Earth's mantle well below the North Island volcano zone is melting
* The eruption of tongariro vomits ashes, damages the hut
* Flashback: Ash spread in Wellington when Ruapehu erupted 70 years ago
* Hot ash rushed up the crater floor of the White Island
With increasing eruption sizes, the likelihood of ashes reaching harmful levels of 10-100mm becomes increasingly significant, especially in Gisborne, Hawke's Bay, Bay of Plenty, Waikato and Manawatū.
In addition, as the eruption becomes larger, ash dispersion becomes less climate dependent, as the formation of a large umbrella cloud can force ashes against wind or crosswind.
For the largest possible eruptions, gray thickness associated with major damage – 100 mm – or severe structural damage – over 300 mm – can be expected at high odds in most major cities of the North Island, even in Auckland or Wellington .
The study was based on a huge amount of background research on the eruptive history of Taupō, from decades of fieldwork by Professor Colin Wilson, co-author of a new article for research on ashes.
Such studies have shown that in the past 12,000 years there have been at least 25 Taupō eruptions spanning 3-4 orders of magnitude, said Dr. Simon Barker, lead author of the article.
Ashfall simulation of an eruption in Taupō producing 1 cubic km of magma under a range of wind conditions.
"Most of the smaller eruptions were similar or smaller in size than the Mt St Helen eruption of 1980. However, the most recent eruption in 232AD was one of the largest and most violent eruptions ever observed on Earth in the last 5000 years, powerful feather of eruption that has reached altitudes of more than 30-40 km, "said Barker.
Research on pumice and the ash chemistry of these eruptions "have suggested that there is still a large system of magmas below Taupō that could generate another eruption on time scales of human concern."
Even without a real eruption, noticeable disturbances such as large swarms of earthquakes or deformations in the ground can have many negative side effects in New Zealand's economy, Barker said.
Simulation of an eruption of 1 cubic km of magma, showing accumulation of ash in real time under a light southwest wind
In the last 1.6 million years, there have been at least four alleged eruptions in the wider Taupō region. The most recent was the Oruanui Eruption, 25,400 years ago.
This event is calculated to have erupted more than 530 cubic kilometers of magma. Nothing ever since, anywhere in the world, has been so great. But one of the four super-eruptions that preceded it was 4 to 5 times greater.
In comparison, it is estimated that the 232AD eruption has reached at least 35 kil km of magma.
One of the objectives of a broader multi-annual program of US $ 8.2 million financed by the government called ECLIPSE is to better understand the upheaval and / or eruptions in Taupō and the evolution (Eruption or Catastrophe: Learning to Implement Preparation for future Supervarication Eruptions) of the volcano. .
The information will be used by scientists, emergency managers, iwi and the community to improve planning and preparation for such an event.
"The area known as the central volcanic zone of Taupō is the most active and productive volcanic system of its kind on Earth," said Barker of the School of Geography, Environment and Earth Sciences at Victoria University in Wellington.
"We know from the geological record that smaller events are more common. For a very large eruption, we expect to see significant upheaval and changes in land around the Taupō region."
There was much uncertainty surrounding whether any future agitation in Taupō would lead to an eruption, Barker said.
"We are trying to better understand what to expect as part of the normal background disturbance in Taupō from geophysical modeling and we are working with the iwi to explore the traditional knowledge of early Maori.
"In turn, estimating the likelihood, timing and impacts of future eruptions (of any size) and isolating the likelihood of another super-eruption remain as major challenges."
The time since the last eruption in Taupō – the 232AD event – was a long period of time for the young Taupō story, which on average erupts every 500 years.
But there was "absolutely no pattern" with the amount of time between eruptions and their size, Barker said. "However, minor events are more common, so statistically, the next eruption is more likely to be minor."
For the ashes study, the researchers modeled five different potential eruption sizes – 0.1, 1, 5, 50 and 500 cubic kilometers. They performed 1000 simulations for each of the five scenarios to see where the ash from an eruption would go under different patterns of atmospheric circulation.
The study was published in the American Geophysical Union Geochemistry, Geophysics, Geosystems.