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Geologists find buried volcano inside Panmure Basin - 22/02/2008

Geologists have found a buried volcano inside Panmure Basin, which is the mouth of a volcano that erupted about 28,000 years ago. It is extremely rare for two eruptions to have occurred at the same site in the Auckland Volcanic Field.


James, Kris and Ian from Prodrill with volcanologist Graham Leonard of GNS Science, looking over lava drilled from below a likely scoria cone found buried in the middle of Panmure Basin

The discovery was made by a group of geologists from government-owned research and consultancy company GNS Science and The University of Auckland as they drilled into the basin from a barge this week to find out more about the volcanic history of volcanoes in the upper North Island.

This is the fifth location that the group has drilled in the past three years as part of a research programme to improve the understanding of volcanoes and help prepare Auckland for future eruptions.

They drilled three holes and recovered the core for analysis. The deepest of the holes was 46m.

One of the drill cores indicates what may be the top of a scoria cone volcano buried under the mud that has filled the basin as the sea level rose following the last glaciation. This is the first time a cone volcano has been found within the Panmure Basin.

Another drill core contains about 2.6 metres of ash that appears to be about 9000 years old. This is a large amount of ash in a small period of time.

Most of this is likely to have come from the nearby Mount Wellington eruption that occurred about 9,200 years ago. Mount Wellington is 1.5km from Panmure Basin.

Scientists from both organisations, including Phil Shane, Ian Smith and Paul Augustinus of The University of Auckland, will now analyse the chemistry of the drill cores to determine the date and the source of each eruption. They will also try to determine the age of the scoria cone.

Project leader Graham Leonard, a volcanologist with GNS Science, said finding what appears to be a new volcanic cone inside Panmure Basin was a very exciting result.

"Most of Auckland’s volcanoes have erupted only once, with the possible exception of Rangitoto. We will now analyse the core to see if Panmure volcano should be added to the list," Dr Leonard said.

It was also important to learn more about the Mount Wellington eruption, as it appeared to be the second most recent Auckland eruption, behind Rangitoto which erupted about 650 years ago.

“The thick ash layers we have found in the Panmure Basin have complicated layering. Studying these will help us better understand the eruptions from which they came.

"Understanding clustering of volcanic eruptions from Auckland Volcanic Field in time and space is very important to preparing for future volcanic activity in the Auckland region.

“This week’s drilling looks like it will give us further clues to possible clustering in the Panmure - Mount Wellington area."

Dr Leonard said the research was timely, as it coincided with Exercise Ruaumoko, a large emergency management exercise focusing on an eruption in the Auckland Volcanic Field.

Drilling is expected to continue until noon on Friday, February 22 and the barge can be accessed by dingy until about that time. After this time the tide may be too low. Access is from the Ireland Road entrance.