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 Verhagen

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.

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