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Thursday, June 23, 2011

Lyttelton eruption 'not possible'

Lyttelton eruption 'not possible'

Last updated 13:02 23/06/2011

Ancient Banks Peninsula volcanoes are not going to erupt, scientists say.

Unnamed officials have been quoted as saying continuing earthquake activity around Canterbury, indicating a volcanic eruption is brewing, has been "hushed up".

Others say the water in Lyttelton Harbour has heated up as a consequence of volcanic activity, and in some parts the water is already too hot to touch.

Some of the country's top earthquake and volcano experts are now determined to quash the gossip before it scares even more people.

Natural Hazards Research Platform manager Kelvin Berryman, of GNS Science, said a Banks Peninsula eruption was "just not possible".

"There's no truth to this. There's no reason for it. We have said time and time again this is not possible," he said.

GNS Science vulcanologist Nico Fournier said the closest pool of magma - underground molten rock - to Canterbury was in the central North Island.

The six million-year-old Banks Peninsula volcanic complex was extinct, he said. The quakes could not reactivate the volcanic area because there was no hot magma there.

"This is supported by all the data recorded by scientists since the main Darfield earthquake in September 2010," he said.

"All the recorded signals - eg, ground-surface deformation from ground-based and satellite techniques, earthquake types - have been strictly tectonic in origin and due to movement along faults, and in no way related to volcanic activity.

"There is no magma any more at depth below Banks Peninsula. The closest magmatic systems are Taranaki-Ruapehu-Taupo, approximately 500 kilometres away.

"Magma residing less than 25km deep below these volcanoes just cannot travel horizontally for such distances.

"Magma is generally lighter than the surrounding rocks and much prefers going up than sideways. And in cases where it does, horizontal distances are tens of kilometres at best, not hundreds.

"So, in a nutshell, magma travelling from the North Island volcanoes to Banks Peninsula, or anywhere near the south of the North Island for that matter, is simply not possible."

Ground shaking had caused liquefaction and had also affected the permeability of the near-surface, leading to changes in the temperature of warm springs and discharge rates that were nothing to do with any volcanic activity, Fournier said.

"In some areas, pre-existing cracks may have opened or closed, affecting the path of the groundwater to the surface. In areas where permeability increases, so may the flow of hot water to the surface," he said. "This can result in an increase in water discharge at the surface, or even new springs. In areas where permeability decreased due to the shaking, hot springs may have experienced a decrease in discharge or even dried out.

"This phenomenon has been observed in many non- volcanic areas around the world after moderate to large earthquakes."

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