THE raw material for the limestone of The Pinnacles came from sea shells in an earlier epoch rich in marine life. There shells were broken down into lime rich sands which were then carried inland by the wind to form high, mobile dunes. Winter rain leached the lime from the sands, cementing grains of sand together in the lower levels of the dunes. Vegetation became established and stabilised the dunes. At the same time, an acidic layer of soil and humus developed over the remaining quartz sand. This acidic soil accelerated the leaching process, and a hard layer of calcrete formed over the softer limestone below. Today this calcrete can be seen as a distinct cap on many Pinnacles and has helped protect the softer limestone below. Cracks formed in the calcrete layer and were exploited by plant roots. Water seeped down among these channels to leach away the softer limestone beneath. These channels gradually filled with quartz sand. The subsurface of the erosion continued until only the most resilient columns remained. The Pinnacles as we see them today were exposed by prevailing winds blowing away the overlying quartz sand.
THE oldest of these, known as the Spearwood dune system, is characterised by yellow or brownish sands. In winter, rain, which is slightly acidic, dissolves small amounts of calcium carbonate as it percolates down through the sand. As the dune dries out during summer, this is precipitated as a cement around grains of sand in the lower levels of the dunes, binding them together and eventually producing a hard limestone rock, known as Tamala Limestone.
At the same time, vegetation that became established on the surface, aided this process. Plant roots stabilised the surface, and encouraged a more acidic layer of soil and humus (containing decayed plant and animal matter) to develop over the remaining quartz sand. The acidic soil accelerated the leaching process, and a hard layer of calcrete formed over the softer limestone below. Cracks which formed in the calcrete layer were exploited by plant roots. When water seeped down along these channels, the softer limestone beneath was slowly leached away and the channels gradually filled with quartz sand. This subsurface erosion continued until only the most resilient columns remained. The Pinnacles, then, are the eroded remnants of the formerly thick bed of limestone. As bush fires denuded the higher areas, south-westerly winds carried away the loose quartz sands and left these limestone pillars standing up to three and a half metres high.
Although the formation of the Pinnacles would have taken many thousands of years, they were probably only exposed in quite recent times. Aboriginal artefacts at least 6,000 years old have been found in the Pinnacles Desert despite no recent evidence of Aboriginal occupation. This tends to suggest that the Pinnacles were exposed about 6,000 years ago and then covered up by shifting sands, before being exposed again in the last few hundred years. This process can be seen in action today - with the predominantly southerly winds uncovering pinnacles in the northern part of the Pinnacles Desert but covering those in the south. Over time, the limestone spires will no doubt be covered again by other sand drifts and the cycle repeated, creating weird and wonderful shapes over and over again.
Kangaroo Point
The turn-off to Kangaroo Point is 7.5 km from the park entrance. A picnic shelter, gas barbecue and toilets are provided at this attractive site near the beach. To the north-west you can see Cervantes at Thirsty Point. Out to sea are the Cervantes Islands. Here, the vegetation has been heavily pruned by the salty winds.
Hangover Bay: The access road to Hangover Bay is 11.6 km from the park entrance. Hangover Bay is a delightful spot with picnic tables, gas barbecues, and a boat launch (four-wheel-drive access only). The stunning bay has a white sandy beach. It offers good snorkeling and occasional surfing.
