Pildappa Rock
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A Bold and Beautiful Rockface Pildappa Rock
Pildappa Rock
Pildappa Rock is a unique pink inselberg located 15 kilometres northeast of Minnipa. Situated in South Australia's granite country, locals proudly proclaim Pildappa to rival the more famous "Wave Rock" - a sandstone wave form located in Hyden Western Australia.
Blue Skies and Pink Granite
Formed about 1500 million years ago Pildappa Rock is part of the vast Gawler Craton - a geological shield structure covering central Eyre Peninsula, the Gawler Ranges and large parts of outback South Australia. Geologists refer to Pildappa Rock and other inselbergs in the area as belonging to the Hiltaba suite of rocks - basically orthoclase rich pink granites dating from Eyre Peninsula's Precambrian age.
Nearby the Gawler Ranges were formed as a result of volcanic action. Unlike the Gawler Ranges however, Eyre Peninsula's inselbergs were formed as Batholiths or granite domes some 7 kilometres below the earth's surface. Clearly much soil erosion has occurred during the past 1500 million years. Equally remarkably, Pildappa Rock and many other Australian inselbergs exhibit very slow rates of weathering - with numerous studies indicating exposed granite surfaces eroding at rates below 50 centimetres per million years.
Pildappa Rock's Flare Structure
Geologists believe the process of flare formation typically involves water runoff seeping into the soil at the base of granite rock faces. Over time, water and permanently moist soil conditions act together to chemically weather away highly reactive granite minerals such as orthoclase and mica. All this can take place at depths of up to 30 metres below the surface. In the case of Pildappa Rock soil levels have also gradually eroded away thereby exposing the prominent flare structure that we can see today.
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1: The name of this Earthcache
2: Observe the rock face. How high up would you estimate the top of the flare structure to be?
3: Can you explain how Geologists believe the Flare Structure is formed?
4: Test the texture of the rock at the bottom of the flare. What can say about how it feels, and why do think this is?
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