Rock of ages
Rugged and wild, the Stirling and Porongurup ranges are national parks that are much loved by WA’s bushwalkers, climbers and hang-gliders.
The Stirling and Porongurup ranges are national parks that are much loved by WA’s climbers, bushwalkers and hang-gliders.
Bluff Knoll is the crown jewel of the Stirling Range – the highest peak in southern WA and the only place in the state to get snow with any frequency. It was my first time here and I’d wanted to make the summit by sunset; within the hour, I was reaping the rewards of that plan.The mist was soon awash with golden light, and the sun’s rays through the clouds picked out details in the landscape below to spectacular effect. I could see why Bluff Knoll captures the hearts of many that visit.
THE STIRLING RANGE and its smaller neighbour – the Porongurup Range – were uplifted about 100 million years ago, when the supercontinent of Gondwana broke up and Australia separated from Antarctica. “When two continents are being pulled apart, you develop a valley – a low point – and on the edges you get mountains, which are called ‘rift shoulders’,” says Professor Ian Fitzsimons, a geologist at Curtin University.
Despite a mere 25km separating the parks, the geology of the two ranges couldn’t be more different.The Stirlings are the remnants of an ancient sea, consisting of many layers of sedimentary rock – mostly sandstone and silt-stone – deposited over a long period, beginning 1.8 billion years ago.
“You get these strong differences as you go up the rock’s profile,” Ian says. “In stormy times, you tend to get coarser particles deposited, whereas finer muds will settle to the seabed during quieter times.”
In contrast, the 1.1–1.2-billion-year-old granite boulders of the Porongurups are igneous and metamorphic rocks formed under high temperatures deep inside the Earth. “They are part of a broad belt of granites exposed along the coast, and are more typical of this Great Southern region of WA, with these rocks also found in Albany, Denmark and Esperance,” Ian says. The stone weathers differently, the alternating hard and soft sedimentary layers giving the Stirlings their characteristic jagged edges and steep cliffs, while the tougher granite of the Porongurups
Shannon is a WA-born environmental journalist with a passion for Australian flora and fauna. Having studied conservation biology and journalism, she hopes to raise awareness of conservation issues through her writing and photography. In 2016 she interned with AUSTRALIAN GEOGRAPHIC in Sydney and has since moved back to Bunbury to freelance for a number of publications.
AS THE LAST of the other climbers began their descent, the chatter and footsteps faded, and I was alone in the silence, 1095m above sea level. Jagged rocks framed the peak’s edge, scraggly shrubs jutting out between the crevices, their branches draped in wisps of lichen. In the distance, the peaks of smaller mountains stood silhouetted in misty haze. It was a view unlike any other in Western Australia.
The view from Bluff Knoll, southern WA’s highest peak.