A forest of stone
The Pinnacles Desert, located within the 19,268-hectare Nambung National Park, presents a landscape of thousands of limestone pillars rising from yellow sand. These structures, some reaching up to 5 meters in height, are the product of complex geological and biological processes that began around 100,000 years ago. The raw material for these pillars is the Tamala Limestone, a type of eolianite, which is essentially wind-blown sand rich in calcium carbonate from marine shells.
The formation process began during the Pleistocene epoch when sea levels were different and coastal dunes, composed of shell fragments and quartz sand, formed along the Western Australian coast. Rainwater, which is slightly acidic, percolated through these dunes, dissolving some of the calcium carbonate. This dissolved lime acted as a cement, hardening layers beneath the surface into a rock known as calcrete.
There are several theories about the exact mechanism that created the pillar shapes. One prominent theory suggests a role for vegetation. As plants grew on the dunes, their roots penetrated the sandy soil. Transpiration drew water towards the roots, and with it, dissolved calcium. This calcium accumulated around the roots, and over time, a hard cast of calcrete formed around them. After the plants died, the surrounding, less-cemented sand and soil were eroded away by coastal winds, leaving the more resistant limestone root casts exposed as the pillars we see today.
An ever-changing landscape
The Pinnacles are not static; they are part of an ongoing geological story. Wind and water continue to sculpt the pillars, and the surrounding yellow sands are in constant motion. This mobile sand has alternately buried and exposed the pinnacles over millennia. In fact, Aboriginal artifacts found in the desert date back at least 6,000 years, suggesting the pillars were exposed then, later covered by sand, and only re-exposed in the last few hundred years.
The composition of the pillars varies. Most are made of well-lithified limestone, but some show clear cross-bedding structures, revealing the changing wind directions that originally deposited the sand. Some pillars have a mushroom-like shape, which occurs when a harder calcrete cap rock erodes more slowly than the softer limestone beneath it. The surrounding desert sand is composed mostly of quartz, providing a color contrast with the pale limestone pillars.
Nambung National Park hosts a diverse range of wildlife, though many species are nocturnal. Visitors might see Western grey kangaroos, emus, and dingoes. The park's reptile population includes bobtail skinks and sand goannas. The flora is also notable, with coastal wattles, acorn banksias, and, between August and October, a bright display of wildflowers.