Mt Taranaki eruption impact area even larger than thought - experts

Experts are warning the impact zone from a large Mt Taranaki eruption is even larger than they imagined.

A new study warns that pyroclastic flows would cover a wider area than previously thought - putting tens of thousands of people at risk.

A pyroclastic flow is a lethal mixture of fast-moving super-heated gas, rock and ash which spew from a volcano.

Previous estimates have put the danger zone at just 10km to 15km. But by analysing old pyroclastic flow deposits for their magnetic signals, University of Auckland researchers have revised this to 25km.

The study's leader, Auckland University PhD student Geoff Lerner, told Newshub this is likely in 15 percent of the largest eruptions. This now requires rethinking emergency management plans as the previous danger zone just covered low-populated areas.

"During most eruptions like Mt Taranaki it's generally thought that the main hazard is five to 15km from the volcano," he told Newshub.

"If you extend it to 25km you reach areas where towns are… it requires a bit of rethinking about the hazards of a pyroclastic flow."

Lerner warns these flows travel at tens of metres per second, and it would take "just minutes" for a pyroclastic flow to reach the 25km boundary.

The new estimates put the more than 85,000 people who live within 30km of the mountain at risk, with a significant danger to regional infrastructure.

This older map shows the areas to avoid in an eruption.
This older map shows the areas to avoid in an eruption. Photo credit: Civil Defence

Red Zone

"This zone, including Egmont National Park, comprises the area most at risk from life threatening hazards," CDEM warns.

"People who remain in this zone are unlikely to survive."

Orange Zone

"This zone includes the area over which significant ground based flows would extend," CDEM says.

"Orange Zone will be evacuated in anticipation of a significant local eruption once the evacuation of Red Zone is underway. Some people who remain in this zone may not survive."

What are the chances

And it's only a matter of time before the volcano erupts. Taranaki Civil Defence Emergency Management (CDEM) warns a volcanic event is "almost certain" within the next 50 years - and the consequences could be "catastrophic".

"An eruption of Mt Taranaki could produce volcanic hazards such as tephra falls, pyroclastic density currents, lava flows, lahars, flooding, debris avalanches, sector collapses, lightning and volcanic gases," it says.

"During unrest and eruption significant earthquakes and ground deformation can also occur."

When it happens, CDEM says the result of a severe eruption could be "catastrophic", with evacuations and "significant disruption" to regional transport links.

"Direct physical and ash fall impacts would potentially damage residential properties, commercial and industrial structures, infrastructure, transport and service routes, and agricultural operations.

"Further hazards may well develop as a result of damage to hazardous chemical and fuel storage areas."

The good news for New Plymouth is it's partly protected by the edifice of the older Pouakai volcano.