The City of Auckland, New Zealand

The Auckland volcanic field.  (NASA by way of Wikipedia)

The Auckland volcanic field. (NASA by way of Wikipedia)

An active volcano should never have the word “city” in its name.

Let’s talk instead about the Auckland volcanic field. This indeed is centered on New Zealand’s most populous urban center and contains 50 or so cones and explosion craters.

Oh, don’t worry about those – it’s the next one that everyone focuses on.

Not Monotonous

Experts at GeoNet – a geological hazards service for New Zealand that’s run by GNS Science – seem to contradict themselves by saying, “Auckland’s existing volcanoes are unlikely to become active again, but the Auckland Volcanic Field itself is young and still active.”

However, it makes sense when you see the true nature of the area as a monogenetic field.

The Greek word monos means “single,” and the existing volcanoes that Aucklanders are busy quarrying or turning into parks are, with a notable exception, just that – one-shot deals.

After each eruption, the magma chimney gets plugged. While this is very bad news in explosive volcanoes, the lava coming from the hot spot that sits about 100 km/62 miles below Auckland is the sort of basalt lava that, like Hawaiian lava, flows more easily than the silica-rich stuff found in nearby volcanic zones like Taupo.

In the Auckland region, a plugged volcano conduit just means the lava spreads sideways until it finds another route up to the surface. The new eruption (which can be explosive if the molten rock comes in contact with water) then clogs its vent, and the process starts all over again.

Rangitoto Island from One-Tree Hill.  (Wikipedia)

Rangitoto Island from One-Tree Hill. (Wikipedia)

The Exception Tests the Rule

Rangitoto, the last one to form, erupted some 500-550 years ago.

This volcano, however, might be different from others in the Auckland field. In April 2013, it was reported that Rangitoto may actually have had several eruptions over a thousand years or so.

In response to the new research, a Civil Defence manager was quoted as saying:

We’re just as safe as we were before the research as we are now, but we understand a little bit more how the field might act.

We also have a very good detection [system] in Auckland. We’ve got some deep bores under Auckland, and when a volcano starts coming up through the hard mantle, it sort of pushes its way through and makes little micro-earthquakes, we can detect those. We’re told by the scientists we’re going to get some warning before it comes up.

Our planning is based on that we will be able to alert Aucklanders that a volcano is occurring, and we believe we will be able to safely evacuate people away from that area.

More information.

Monitoring. (Note: Links to this and other NZ volcano online monitoring information are down at the time of writing; hopefully, it will be back up by the time you read this.)

Webcams.

Awesome Rangitoto Eruption Simulation by the Auckland Museum (recorded by a visitor).



Categories: Sunday morning volcano

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