The Pinnacles Desert

The Pinnacles Desert, in Nambung National Park north of Perth, Western Australia, is a field of thousands of limestone pillars, ranging from a few centimeters to more than three and a half meters tall, rising from a bed of yellow sand. The limestone originated as marine shell fragments deposited as coastal dunes tens of thousands of years ago and cemented by rainwater into a soft rock unit; roots from ancient vegetation growing over the dunes helped channel percolating rainwater into vertical cavities, dissolving and cementing the surrounding limestone in ways that reinforced a network of pillar-shaped cores, and after the overlying vegetation and less-cemented dune sand eroded away, the remaining pillars were left exposed above the desert surface. The exact sequence of dune deposition, cementation and exhumation remains debated among geologists, but the pillars are recognized as a striking example of coastal dune-derived pinnacle karst.