Region’s sleeping giant

• Date: 24 March 2021
• Author: Jamie Morton
• Published date: 24 March 2021
• Publication title: Stratford Press

The imposing, 2500m-high stratovolcano is considered to be in a “quiet period” — its last eruption occurred in 1790 — making it among its longest on record.

Based on an analysis of nearly 230 eruptions over the last 30,000 years, researchers have put the probability of a new eruption at between one and 1.3 per cent each year.

While the probability is low, the risk is significant: more than 85,000 people live within 30km of the mountain, with 40,000 in high-priority evacuation areas.

A recent estimate of the net losses in economic activity from a brief Taranaki eruption was crudely estimated at between $1.7b and $4b — or between $13 billion and $26b over a decade of volcanism.

The volcano’s fiery history has been laid out in a sprawling new review, bringing together 25 years of research, and published in the New Zealand Journal of Geology and Geophysics.

“What has emerged from this analysis is the realisation of how Mt Taranaki represents the most recent of a long lineage of volcanoes that extends from west of Auckland, all the way down the western offshore margin of the North Island,” University of Auckland volcanologist Professor Shane Cronin said.

Those Taranaki volcanoes we could see today — Taranaki, Pouakai, Kaitake and Paritutu — represented just the last 1.7 million of about 40 million years of activity in the North Island’s western volcanic province.

While Taranaki eruptions had been variable over time, in scale and frequency, scientists had still been able to observe a regular pattern of “busy times” lasting 1000 to 1500 years.

Over the past 3000 years, there have been about seven periods where tens to hundreds of individual eruption events took place, and only perhaps a few that could be considered one-offs.

In one period, about 2000 years ago, there were at least 11 extremely large ash-producing events that spewed ash across vast areas of the North Island.

The most recent eruption period — called the “Maero eruptive period” — came between 1000AD and 1790.

In these unsettled periods, Cronin said eruptions typically happened every 20 to 30 years, compared with once a century in the slow times.

“We are in a slow period at the moment, so we expect that once it begins erupting again, it will resume the ‘busy’ frequency.”

Taranaki’s next eruption

Scientists have been able to sketch out several specific scenarios that have repeatedly played out in the past.

Past eruptions have come from both Taranaki’s summit and Panitahi/Fanthams Peak — and it was...