Saturday, February 23, 2008

Discovery of buried volcano

Geologists have discovered a buried volcano inside Auckland's Panmure Basin while drilling to find out more about the volcanic history of the area.

The GNS Science team were drilling from a barge at the basin, itself the mouth of a volcano that erupted about 28,000 years ago.

The new volcano is believed to date back to a similar point, and experts are already hailing it as an exciting find that gives a greater understanding to the clustering of volcanic eruptions in the Auckland region.

Auckland sits on 49 volcanoes, so dragging up a fiftieth from the murky waters of the Panmure Basin is exciting, but perhaps not suprising. However, GNS scientists say it is extremely rare for two eruptions to have occurred at the same site in the Auckland volcanic field.

Dr Graham Leonard of GNS Science says the discovery means that "there are two different types of eruptions going on here - the very explosive one, for the basin, and the fire fountaining to produce the cone in the middle of the lake."

New Zealand geologists hold particular interest in sites like Orakei, Lake Pupuke, and the Panmure Basin. In most cases, these soft spots in the earth can hold the answer not only to the past, but the future.

Leonard believes that the new site is "a nice record" that will help researchers understand what happened at Mt Wellington.

This would be no small feat, considering that Mt Wellington is several milennia younger than the basin cones. It only blew its top around nine thousand years ago.

While it is unusual for eruptions to happen twice in the same place, Leonard's team have based on the large flow of magma 80 kilometres below the area's surface.

"You can imagine something coming to the surface from 80 kilometres' depth would find several pathways to that surface."

In fact, it would not even be a first for Auckland. A repeat eruption happened on Rangitoto only 650 years ago.

The drilling was part of a three-year project intended to gain insight into Auckland's volcanic history, and perhaps prepare the city for another big bang. Core samples will be analysed at Auckland University to try to work out the exact dates of each eruption.

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