A Recurrence Rate of 2000 Years
Using the latest dating techniques, scientists from the University of Melbourne's School of Earth Sciences and the
Melbourne School of Engineering have calculated the ages of the small volcanoes in the regions and established the
recurrence rate for eruptions as 2,000 years.
With the last volcano eruption at Mt Gambier occurring over 5,000 years ago, scientists say the areas are overdue.
The research was presented by Professor Bernie Joyce of the University of Melbourne's School of Earth
Sciences at the XXV International Congress of Geodesy and Geophysics, in Melbourne.
"Although the volcanos 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 2,000 years," Professor Joyce said.
Small Monogenetic Eruptions
"These are small eruptions and very localised but depending on the type of eruption, they could cause devastation to
thousands of people," he said.
The regions of Western Victoria and adjacent south-eastern South Australia demonstrate a history of activity by young
monogenetic (single short-lived activity) volcanoes. Similar young monogenetic provinces are found in northeast Queensland.
Hundreds of Small Volcanoes, Flows and Craters
Professor Joyce and his colleagues from the University's School of Earth Sciences have spent years cataloguing the
hundreds of small volcanic cones, lava flows and craters in the regions. The distribution of activity including lava
flows and ash deposits has been mapped in detail.
The latest findings are due to more recent studies using a range of state of the art dating techniques, which have
provided more information on the ages of the individual volcanoes, providing information about the occurrence rates.
Professor Joyce said there are several kinds of eruptions which can cause damage and harm to local communities.
Preparing for Volcanic Hazards
"Among the hazards which may need to be prepared for in this closely-settled region are the localised effects of cone
building leading to lava flows which run downhill towards the coast.'
"The long lasting and often extensive lava flows can travel for tens of kilometres, and so would be hazardous to modern
infrastructure such as bridges, roads and railways, powerlines and pipelines, as well as being a major fire hazard on
the dry grassland plains of summer in Western Victoria."
Ground Water Interactions and Steam Explosions
"In some cases rising magma can meet ground water and cause steam explosions. This can form wide craters and produce a
lot of ash."
"Depending on where the eruption occurs, ash can cause huge damage to people who are down wind, clogging up streams,
road and rail transport and perhaps affecting local air travel," he said.
What Causes these Eruptions?
The cause of the volcanic activity may be the movement of the Australian tectonic plate, which is moving north.
"The plate is hitting up against PNG, lifting the southern margin upwards. This allows magma to move upwards towards
the surface, " Professor Joyce said.
Developing Action Plans
Professor Joyce said communities need to have some knowledge of what to do after an eruption. "So far we have no action
plans in place if eruptions occur. 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 areas such as Colac, Port Fairy, Portland and Mt Gambier."
"We need to note the concerns of other cities such as Auckland in New Zealand which sits on a similar young volcanic region,
with a local government which has plans in place to respond if eruptions occur," he said.
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| Sitting near Australia’s rugged southern coast, the South Australian town of Mount Gambier is built on the side of an extinct volcano that last erupted between 4,300 and 28,000 years ago. Since that time, the caldera of the volcano has filled with rainwater, forming a very deep lake that provides the town with water. The large caldera lake is called Blue Lake due to a rather peculiar characteristic: the water turns a brilliant cobalt blue during the summer and early fall (approximately November-March). The photo-like image of Mount Gambier was acquired from low-earth orbit by the Landsat 7 satellite’s Enhanced Thematic Mapper Plus (ETM+) instrument on October 1, 1999. |
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