Much of NZ 'dotted' with little-known volcanoes, scientist reveals

Most New Zealanders are familiar with our big volcanoes like Ruapehu and Taranaki - but there are lesser-known volcanoes "dotted" over much of the country, a scientist has revealed.

Northland, for example, was built on a volcanic field, much like Auckland, GNS Science principal scientist Graham Leonard told Saturday Morning.

It was made up of scoria fields, lava flows and explosion craters.

The volcanoes were not talked about much because they were "not quite as frequently active, but also we don't have a third of the country's population living on top of [them]".

There were two separate clusters of volcanoes in the Northland region - one around Whangārei and one through the Kaikohe and Bay of Islands area.

Anyone driving out of Whangārei, through Kamo, would see "several little scoria cones, just like Mt Eden" - those were volcanoes, Leonard said.

In Auckland's south, the Pukekohe area had also seen "a lot of volcanism", he said.

"The beautiful soils there for growing vegetables are all volcanic.

"That's where it used to be [active] before Auckland and for some reason it migrated slowly up to Auckland."

Coromandel was also volcanic, but the field was now "basically extinct" as the subducting plate underneath the North Island had moved and deepened over millions of years.

That same plate was responsible for a cluster of extinct volcanoes around the Tauranga hills.

South Auckland, Otago and Canterbury were home to "an odd kind of diffuse volcanic area" which was "still very occasionally popping off now", Leonard said.

That included the entirety of the Otago Peninsula, which was "one big volcanic complex".

One of the youngest volcanoes in the country was Timaru's Mt Horrible, which was now extinct.

The city was built on lava flows from the volcano, which gave it its undulating appearance.

"The reason you've got good rock at Timaru for a port is it's volcanic."