Postcards From Eden
Postcard 6
Edition of 40
Photographic montage
5" x 7"
Original image - Pinnacles Nambung National Park
Cervantes Western Australia

In the Pinnacles Desert, right in the heart of Nambung National Park, thousands of huge limestone pillars rise out of a stark landscape of yellow sand. In places they reach up to three and a half metres tall. Some are jagged, sharp-edged columns, rising to a point; while others resemble tombstones. The raw material for the limestone of the pinnacles came from sea shells in an earlier epoch rich in marine life. These shells were broken down into lime-rich sands which were brought ashore by waves and then carried inland by the wind to form high, mobile dunes. Three old systems of sand dunes run parallel to the WA coast, marking ancient shorelines. 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 theremaining 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.