Down Under Volcanoes

Where.

Geologists have discovered three previously unrecorded volcanoes in volcanically active southeast Australia.

The new Monash University research, published in the Australian Journal of Earth Sciences, gives a detailed picture of an area of volcanic centres already known to geologists in the region.

Covering an area of 19,000 square kilometres in Victoria and South Australia, with over 400 volcanoes, the Newer Volcanics Province (NVP) features the youngest volcanoes in Australia including Mount Schank and Mount Gambier.

Focusing on the Hamilton region, lead researcher Miss Julie Boyce from the School of Geosciences said the surprising discovery means additional volcanic centres may yet be discovered in the NVP.

Victoria‘s latest episode of volcanism began about eight million years ago, and has helped to shape the landscape. The volcanic deposits, including basalt, are among the youngest rocks in Victoria but most people know little about them,”Miss Boyce said.

“Though it’s been more than 5000 years since the last volcanic eruption in Australia, it’s important that we understand where, when and how these volcanoes erupted. The province is still active, so there may be future eruptions.”

The largest unrecorded volcano is a substantial maar-cone volcanic complex, a broad, low relief volcanic crater caused by an explosion when groundwater comes into contact with hot magma, identified 37 kilometres east of Hamilton.

Miss Boyce said the discoveries were made possible only by analysing a combination of satellite photographs, detailed NASA models of the topography of the area and the distribution of magnetic minerals in the rocks, alongside site visits to build a detailed picture of the Hamilton region of the NVP.

“Traditionally, volcanic sites are analysed by one or two of these techniques. This is the first time that this multifaceted approach has been applied to the NVP and potentially it could be used to study other volcanic provinces worldwide.”

The NVP is considered active, as carbon dioxide is released from Earth’s mantle in several areas, where there is a large heat anomaly at depth. With an eruption frequency of one volcano every 10,800 years or less, future eruptions may yet occur.

It’s hoped that this multifaceted approach will lead to a better understanding of the distribution and nature of volcanism, allowing for more accurate hazard analysis and risk estimates for future eruptions.

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Why.

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Scientists have solved a long-standing mystery surrounding Australia‘s only active volcanic area. The volcanism springs from a unique interaction between the continent’s movement north and local variations in its thickness.

The research explains a volcanic region that has seen more than 400 volcanic events in the last four million years. The 500 kilometre long region stretches from Melbourne to the South Australian town of Mount Gambier, which surrounds a dormant volcano that last erupted only 5,000 years ago.

“Volcanoes in this region of Australia are generated by a very different process to most of Earth’s volcanoes, which occur on the edges of tectonic plates, such as the Pacific Rim of Fire,” says lead researcher Dr Rhodri Davies, from the Research School of Earth Sciences.

“We have determined that the volcanism arises from a unique interaction between local variations in the continent’s thickness, which we were able to map for the first time, and its movement, at seven centimetres a year northwards towards New Guinea and Indonesia.

The volcanic area is comparatively shallow, less than 200 kilometres deep, in an area where a 2.5 billion year-old part of the continent meets a thinner, younger section, formed in the past 500 million years or so.

These variations in thickness drive currents within the underlying mantle, which draw heat from deeper up to the surface.

The researchers used state-of-the-art techniques to model these currents on the NCI Supercomputer, Raijin, using more than one million CPU hours.

“This boundary runs the length of eastern Australia, but our computer model demonstrates, for the first time, how Australia‘s northward drift results in an isolated hotspot in this region,” Dr Davies said.

Dr Davies will now apply his research technique to other volcanic mysteries around the globe.

“There are around 50 other similarly isolated volcanic regions around the world, several of which we may now be able to explain,” he said.

It is difficult to predict where or when future eruptions might occur, Dr Davies said.

“There hasn’t been an eruption in 5,000 years, so there is no need to panic. However, the region is still active and we can’t rule out any eruptions in the future.”

The research is published in the Journal Geology.


 

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