In February 2008, geologists from GNS Science and Auckland University discovered a new volcano while drilling in the Panmure Basin in Auckland.
The reason they hadn’t found the volcano before was that it was buried inside another much larger volcanic basin, and it is extremely rare for two eruptions to have occurred at the same site in the Auckland Volcanic Field. The old volcano, known as the Panmure Basin, erupted about 28,000 years ago, but the new volcano buried in the mouth of the old one could be younger than 10,000 years old.
Volcanologist Dr Graham Leonard said the find was very exciting. "Most of Auckland’s volcanoes have erupted only once, with the possible exception of Rangitoto. We will now analyse the (drill) core to see if Panmure volcano should be added to the list."
The group of geologists has made several drill holes around the Auckland region, the research is to improve our understanding of volcanoes and help prepare Auckland for future eruptions.
The volcano was discovered when one of the drill cores indicated what is likely to 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 - a glaciation is a period when glaciers advance and cover more area, this is not the same as an ice age, where large areas of ground are frozen. The last glacial period in New Zealand ended around 20,000 years ago. 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 9,000 years old. This is a large amount of ash in a small period of time. The geologists think that most of this ash is likely to have come from the nearby Mount Wellington eruption that occurred about 9,200 years ago. Mount Wellington is 1.5 km from Panmure Basin. However, they will now need to analyse the chemistry of the drill cores further to determine the date and the source of each eruption. They will also try to determine the age of the scoria cone.
The geologists currently believe that the Mount Wellington eruption is the second most recent Auckland eruption, behind Rangitoto which erupted about 650 years ago. They are interested to see if the new volcano changes this.
For more information about Auckland’s volcanoes see this GNS Science website page.