Auckland could have similar volcanic eruption to the one drawing crowds in Iceland

Thursday, 25 March 2021

Members of the public have been advised to stay away, and the main road from the capital region to Keflavik airport was temporarily closed.

A volcanic eruption similar to the event drawing crowds in Iceland could be in Auckland’s future.

Professor Jan Lindsay, a volcano researcher at the University of Auckland, said the type of eruption under way in Iceland was “absolutely” similar to something that could happen in Auckland.

“The style of eruptions that occur in Iceland are similar to what you might expect in Auckland, in a broad sense that we could have fluid lava coming out of the ground in Auckland,” Lindsay said.

Lava flows from the eruption of a volcano on Iceland’s Reykjanes peninsula.

“But the setting is a little bit different. They’re on a mid-ocean spreading ridge in Iceland, so they have a lot of volcanism. It’s more common.”

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People are keen to see the eruption for themselves.

The lava coming up in Iceland seemed more fluid than she would expect in Auckland, but an eruption in Auckland may look something like the one in Iceland now.

One difference was that some eruptions in Auckland had started more explosively, whereas the lava was just flowing out of a fissure in Iceland’s eruption.

Rangitoto is named after an ancient captain’s bloody nose.

“When magma comes into contact with water, the water expands and causes the magma to break apart and fragment and explode, kind of,” Lindsay said.

“You have explosion craters, which we have peppered all over Auckland.”

The crater on Mt Eden/Maungawhau in Auckland.

Volcanoes in Auckland, and for the most part in Iceland, produced basaltic magma, which could end up as scoria.

The most recent eruption in Auckland was at Rangitoto. It probably erupted about 600 years ago, and there may have been another eruption about 50 years after that.

“It started out probably with one of those explosions, then eventually developed a scoria cone, which is what this volcano may turn into in Iceland,” Lindsay said.

“Then at the very end there were outpourings of lava to make that beautiful round shield around the volcano. The lava may not have been as fluid as in Iceland, but some of it may have been.”

Eruptions started 193,000 years ago on the Auckland Volcanic Field (AVF), and at least 50 volcanoes have appeared since then.

A 2017 paper by Ross Roberts and Graham Leonard said there were no grounds to be able to forecast when or where the next eruption in the AVF would be.

The difficulty in forecasting was highlighted by the fact the most recent eruption – Rangitoto – was unusual compared with others in Auckland. It was nearly four times larger than any previous eruptions in the field, erupted magma of a different chemistry, and happened after an unusually long 10,000-year gap.

The authors said a future eruption in Auckland would be “relatively small”, but they also noted the rate of volcanism in the field had increased since 60,000 years ago, suggesting the field was still in its infancy.

In Iceland, crowds are flocking to watch as lava oozes out of the ground in the uninhabited Geldingadalur valley, not far from Iceland’s capital of Reykjavik.

Tens of thousands of mostly small earthquakes had indicated magma was moving beneath the valley, and about a week ago lava broke through the surface near Fagradalsfjall, one of several shield volcanoes on the Reykjanes peninsula.

The lava poured from a fissure that started out about 500 metres to 700m long. The lava is building up, and then breaking down, leaving mounds of cooled lava called spatter cones.