Volcanic eruptions long overdue in SE Australia

By Campbell Phillips 7 July 2011
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Victoria and South Australia should have better plans in place for dangerous eruptions.

NEW RESEARCH HAS revealed the age of extinct volcanoes in western Victoria and South Australia, confirming that both regions are overdue for a potentially devastating eruption.

Scientists from the University of Melbourne have calculated the ages of small, long-dead volcanoes across both states and have estimated that new eruptions typically occur every 2000 years or so. But the last eruption at Mt Gambier in South Australia – the nation’s most recently active volcano – was 5000 years ago, meaning that a new volcanic event is long overdue.

Professor Bernie Joyce of the University of Melbourne’s School of Earth Sciences presented the findings earlier this week at the 25th International Congress of Geodesy and Geophysics, in Melbourne.

“Although [new] volcanoes in the region don’t erupt on a regular sequence, the likelihood of an eruption is high given the average gap in the past has been 2000 years,” Bernie told Australian Geographic. “These are each small eruptions and very localised, but they could cause devastation to thousands of people.”

Lava flows

The latest findings are the result of state-of-the-art rock-dating techniques, which have provided more information on the ages of the individual volcanoes. “Thermo-luminescence and optically stimulated luminescence (OSL) are both new dating techniques that have improved our ability to date geological structures more accurately than we have before,” Bernie says.

Any eruption would be relatively small, but there is still some cause for concern, he says. “We’re not going to see anything on the scale of Mt St Helens or Vesuvius. Being monogenetic [the kind that only erupts once], these volcanoes have a limited lifespan and any damage would be localised.”

It is the disruption to infrastructure that would cause the biggest problems, Bernie says. Lava flows could create fires and cause damage to roads, power and gas lines, while rising magma could trigger subterranean explosions when it comes into contact with ground water. “Depending on where an eruption occurs, ash can cause huge damage to people who are downwind, clogging up streams, road and rail transport and perhaps affecting local air travel,” he says.

Volcanic activity usually occurs along the margins of tectonic plate boundaries and it’s surprising that mainland Australia (hundreds of kilometres from the edge of a plate) has sites of possibly active volcanoes. But stresses and strains in the middle of tectonic plates can lead to earthquakes and volcanic activity, say experts. In this case, “the Indo-Australian plate is hitting up against Papua New Guinea, lifting the southern margin [of the plate] upwards. This allows magma to move upwards towards the surface [from deep in the Earth],” Bernie says.

Volcanic outburst

Professor Richard Arculus, of the Australian National University’s Research School of Earth Science, doesn’t believe the cause of this kind of volcanic activity is certain, but agrees that volcanic activity is something we need to be prepared for in Australia.

“The major question regarding this prediction relates to our poor understanding of the cause of volcanism in this region,” he says. “While the creation of relatively small volcanic fields such as those of western Victoria and in South Australia remains controversial, it is no doubt better to be prepared than caught unawares by a new volcanic outburst.”

Experts agree that Australia should have detailed emergency plans in place similar to those that exist in New Zealand. “So far we have no action plans in place if eruptions occur,” says Bernie. “If they happen close to Melbourne or Geelong it could be hugely devastating. It is more likely however, that eruptions would occur further west, closer to [less populated] areas such as Colac, Port Fairy, Portland and Mt Gambier.”

In related news a 4.4 magnitude earthquake struck the south of Victoria on Tuesday, showing the power that geological activity can exert in the region.

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