When people think of Australia, volcanoes are probably not the first thing that springs to mind.
However, Australia contains several active but low risk volcanoes. And by active volcanoes,
I am not referring to the McDonald or heard islands. Rather, I am referring to the Australian
mainland. In the last 10,000 years, three states have experienced volcanic eruptions.
This video will discuss the most recent eruptions in both Victoria and South Australia,
and analyze the general hazards which the associated volcanic field poses in the future.
In portions of both western Victoria and eastern South Australia, there are a number of unusual
geologic formations. One of these formations is a recent volcano located within the town of Mount
Gambier. This volcano is one of more than 400 vents which are part of a vast volcanic field.
The volcanic field I am referring to is the newer volcanics province, which covers
an area of 15000 square kilometers. The newer volcanics province began
forming 4.5 million years ago, when magma from the east Australian hotspot began
moving across southeastern Australia. The first period of activity created both shield volcanoes
and cinder cones south of Ballarat but also west of Melbourne. One of the earlier vents in this
field is known as Aitken hill, which formed 3.8 million years ago. It is inferred that
eruptions from this low prominence hill created fountains of lava and produced relatively fast
moving lava flows due to its shallow slope. Around 2.6 million years ago, this volcanic
field created an interesting formation known as basalt columns. Although these look artificial due
to their hexagonal shape, these formed naturally due to a fracture pattern within lava. As the lava
cooled, this shape propagates downwards, leading to the creation of interesting columns. This area
can be visited in the Organ Pipes National Park. Over the next several million years,
volcanic activity began trending westward with low frequency eruptions.
Eventually, eruptions occurred in a portion of South Australia to form several features
such as Mount Burr and Mount Buirhead. In the last 10,000 years, this large
volcanic field created three different volcanic eruptions. The earliest of these eruptions formed
a compound volcano in Victoria known as Red Rock in 5850 BC. Several explosive eruptions
occurred at this volcano, which formed a number of volcanic craters known as maars.
The two most recent eruptions both occurred in South Australia near the border with Victoria.
5000 years ago, a series of eruptions created the Mount Schank cinder cone. To the south of
the main eruptive vent, you can see two smaller craters in addition to the central crater. These
craters indicate that a portion of this volcano's activity included explosive eruptions, likely
due to the interaction of magma with groundwater. The most recent eruption occurred 10.5 kilometers
north of Mount Schank. This series in 2900 BC formed one of the four craters at Mount
Gambier, referred to as Blue Lake. This crater is more than a kilometer wide, and formed in a
highly explosive eruption that did not erupt any lava referred to as a phreatic eruption.
So, what hazards does this volcanic field pose, and how dangerous is it?
Using the classification system from the US geological survey, the newer volcanics
province would be collectively rated on the lower end of the moderate threat category.
Eruptions from this field are infrequent, occurring about once every ten thousand years.
The reason why it is rated as moderate threat instead of low threat is due to the likelihood
of future explosive eruptions. These explosive eruptions such as the one which formed Blue Lake
are difficult to predict. When they occur, a powerful explosion creates a short distance
pyroclastic flow, and large boulders get thrown several kilometers away. However,
the next eruption might not be very explosive, but rather effusive. It could produce fountaining lava
to create a low prominence cinder cone or shield volcano. This type of eruption poses a minimal
hazard due to the lava flows. Overall, the odds of a new eruption occurring in this vast volcanic
field is about 1 in 10,500 each year. I hope that you enjoyed this video!
If you would like to request a specific topic, please leave a comment below!