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Geology, Geology Talk

The Glasshouse Mountains, as viewed from the Mary Cairncross Scenic Reserve on the Sunshine Coast.
The Glasshouse Mountains, as viewed from the Mary Cairncross Scenic Reserve on the Sunshine Coast.

The Glasshouse Mountains: A geological wonder

Continuing his insights into fascinating geological highlights, Bill Langer this month takes us close to home – to the breathtaking sight of the Glass Mountains…

“These hills… are remarkable for the singular form of their elevation, which very much resembles a glass house, and for this reason I called them the Glass Houses…” 

Captain James Cook, 17 May, 1770

Back in 2004, my wife Pam and I had the pleasure of visiting Queensland, where I was a keynote speaker at the IQA’s annual conference. While we were there our hosts and friends Andy and Jo Stephens showed us around the Queensland countryside.

One fascinating place we visited was a tropical rainforest at Mary Cairncross Scenic Reserve on the Sunshine Coast. Andy cautioned us about leeches and ticks, both of which live in the rainforest. As if to prove his point, while Andy was walking through the forest a tick took up residence on his bum. But that’s another story.

The topic of this article is the Glasshouse Mountains, a group of 11 hills that we viewed from Mary Cairncross. Captain James Cook spied them in 1770 as he sailed his research vessel HMS Endeavour up the coast of what is now Queensland.

Mount Tibrogargan – the “father” – stands at 364m.
Mount Tibrogargan – the “father” – stands at 364m.

The Glasshouse Mountains have been, and continue to be, of spiritual significance to the Aboriginal people of the region, particularly the Gubbi Gubbi people. According to Gubbi Gubbi legend, the mountains are a family. Mount Tibrogargan (364m) is the father, Mount Beerwah (the highest peak at 556m) is the mother, and the other peaks are the children, including Mount Coonowrin (377m).

One day Tibrogargan saw the ocean flooding the coast and he fled inland with his family. Tibrogargan told his son Coonowrin to help Beerwah and his siblings move to safety. Coonowrin was afraid and ran away. When his father found him he hit him on the back of the head, resulting in Coonowrin’s crooked neck. Tibrogargan was ashamed of his son’s cowardice and turned his back on him, never to look on him again.

However, the mountains didn’t form quite like the legend says. Sixty-five million years ago, Australia was further south than it is today, and still part of the ancient super continent of Gondwanaland. Much of Australia was covered in tropical rainforest similar to that at Mary Cairncross. Eventually, Australia separated from Antarctica and began drifting northwards.

About 29 million years ago southeast Queensland moved over a “hot spot” in the Earth’s mantle, resulting in prolonged volcanic activity. Volcanoes spewed out lava flows, building up broad, gently sloping plains. A few million years later, magma was forced upwards through the older rocks, making large bulbous plugs and laccoliths, and filling volcanic necks.

After millions of years of erosion, the surrounding softer sandstone rocks were worn away. The more resistant volcanic rocks are now exposed as the steep-sided peaks of the Glasshouse Mountains. Some of the older lava is quarried today for aggregate but much of the older lava was weathered into fertile soils that enable rainforests such as Mary Cairncross Scenic Reserve to re-establish and thrive, ticks and all.

This brings us back to Andy’s bum. We got to see the tick only after his wife Jo had carefully removed it. What a relief!

Bill Langer
Independent Research Geologist

Bill Langer is a freelance writer and retired Senior Research Geologist for the U.S. Geological Survey. Bill is now an independent researcher specialising in aggregate resources. Click here to email Bill or visit his website.
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Monday, 26 August, 2019 1:48pm
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