Eruption scenario forces out 435,000

Scientists have imagined a twomonth-long volcanic eruption near Mangere Bridge, in which 435,000 residents would be forced to flee.

The paper, focusing on what would happen to Auckland’s transport network, found most physical damage to road and rail transport would be from the eruption itself, destroying anything within 0.5km to 2.5km, but with little impact from quakes leading up to the eruption.

In this scenario, Auckland Airport would not be damaged but would have restricted access from evacuation zoning and airspace restrictions, forcing limited domestic and cargo flights to redirect to Whenuapai and Ardmore Aerodrome.

After the eruption, the researchers say, the most important factors for keeping the transport network open are cleaning bottleneck areas like bridges of tephra (rock particles), ensuring electricity supply for the trains, airport and traffic signals and ensuring continued fuel supply.

The University of Canterbury, University of Auckland and GNS Science researchers behind the new study, published in the Journal of Volcanology and Geothermal Research, said the biggest service reduction across all transport networks would occur about six days before the eruption.

This was largely because of the evacuation zones be implemented, disrupting crucial north-south ground links through Auckland.

In the main scenario, ash on roads and rail would likely cause some disruption for more than a month.

“The volcanic activity in the scenario progresses from seismic unrest, through phreatomagmatic explosions generating pyroclastic surges to a magmatic phase generating a scoria cone and lava flows,” the researchers reported.

“We find that most physical damage to transportation networks occurs from pyroclastic surges during the initial stages of the eruption.”

The scenario also meant visibility would likely be reduced and lower speed limits might have to be implemented to reduce the amount of ash being re-suspended into the air.

Wind direction and strength would be a big factor in ash eruptions.

Uncertainty on the potential location of the volcanic vent before any eruption would mean residents would be displaced for longer.

The researchers said working with transport infrastructure providers and emergency management officials was “crucial” to help examine what might occur on Auckland’s transport networks during an eruption and the subsequent recovery.

Much of Auckland is at risk — more than 50 volcanoes lie beneath a field stretching across 360sq km — and more than one million people live on areas where an eruption could occur.

An eruption from one of the Auckland Volcanic Field’s many volcanoes could blast out an explosion crater 1km to 2km across, destroying everything in it, but planners believe people in its path would be evacuated well before an event.