Australia's mountains are still growing

Australia has often been portrayed as an old and idle continent with little geological activity, but new research from The University of Melbourne suggests that we remain geologically active and that some of our mountains are still growing. Indeed, the team’s study reveals that parts of the Eastern Highlands of Victoria, including popular skiing destinations such as Mt Baw Baw and Mt Buller, may be as young as five million years old — not 90 million years old as previously thought.

John Engel is one of four scientists from Melbourne’s School of Earth Sciences who studied the stalagmites, stalactites and flowstones — technically called ‘speleothems’ — in the nearby Buchan Caves to produce the findings, which have been published in the journal Geology. He stated, “At least 250 m of additional height in the East Victorian Highlands appears to have been gained in the last few million years.”

With the help of Parks Victoria rangers, Engel and the team visited 10 caves, climbing down through the passages and crawling through tight squeezes to collect small fragments of speleothem ‘rubble’ to take back to the lab to determine their age, using radiometric U-Pb dating.

“Our research shows a clear trend between oldest speleothem (cave age) and height in the landscape,” Engel said. “The data suggests that the Buchan region has been steadily uplifting at a rate of 76 m every million years, beginning at least 3.5 million years ago and continuing today. This means that some speleothems have been sitting in dark caves undisturbed for 3.5 million years.”

Evidence suggests the Highlands originally rose up about 90 million years ago when the Tasman Sea between Australia and New Zealand opened up. Researchers say the cause of the more recent uplift is debated, but a leading theory points to the friendly rivalry with New Zealand.

“The Australian and Pacific plates share a common boundary, and many of the forces involved at this boundary may be propagated into the Australian plate as tectonic stress,” Engel said. “Some of this tectonically induced stress is then released as uplift of the mountains in South East Australia.

“This is why East Gippsland may still feel effects related to these tectonic forces. This subtle modification of classical plate tectonic theory can help explain the frequent, small earthquakes observed along South East Australia.”

Engel said uncovering the secret stories surrounding when and how mountains form provides a layer of appreciation as well as an active field of research for geologists.

“Our research showcases a new — and rather unique — method for measuring the uplift of mountains. This technique of using speleothem is likely to also work in other caves across the world for regions with ‘recent’ tectonic activity, offering geologists great opportunities to share more stories about these impressive and unchanging features of our landscape.”

Image caption: Scientist Jon Woodhead uses a custom-made machine with a diamond-tipped drill to carefully extract speleothem ‘rubble’ for analysing. Image credit: John Engel.

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