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Perth, |
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'Cliffs in danger of collapse'
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Rottnest has 300 places where limestone cliffs are in danger of collapsing. This is the conclusion of Ray Gordon, a geologist who has just spent eight days on the island surveying the risk areas. He said the area near Devil's Elbow on The Esplanade, Peppermint Grove, was also particularly unstable because it had been a colonial quarry and explosives had been used to blast the rock clear. He said the Rottnest areas near the lighthouse and above The Basin swimming rock pool were particularly dangerous and should be fenced off with warning signs. He said: "If people still insist on going through the barrier, then they take that risk on themselves." Camping or lighting fires in caves was particularly dangerous because it could cause rocks to expand and break. Mr Gordon has spent 40 years studying limestone in WA - and has had several close escapes from rock falls. He does regular inspections of caves and rocky slopes in King's Park, Peppermint Grove and Cottesloe. Quarry explosions at Peppermint Grove had made cracks in the remaining limestone, and tree and shrub roots grew into the cracks, growing wider and creating more pressure. Another major factor was that limestone had billions of empty air spaces which could hold water. This water added enormous weight to the mass. If there were cracks and undercutting from waves, water or wind, then a collapse could occur at any time. Mr Gordon, who was called in as an expert to investigate the tragic Gracetown collapse, said: "That's what happened there. "It was an overhanging rock shelf which people used for shade in summer and shelter in winter. "The rock had cracks and already had a high water content and that day it had been raining. "Sometimes it can be just enough for a particular shower to tip the scales." He said big rocks in the shallows at Freshwater Bay near the Scotch College rowing shed showed how boulders had fallen from the cliff years go. He said there was a constant risk. Cliffs and caves should be closely monitored and, where appropriate, fenced off, filled in, shored up or pinned. • Mr Gordon will be awarded with high honour next week
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