How did the Pinnacles in Western Australia form?

How did The Pinnacles in Western Australia form?

By Jenny Li | 3:18pm Aug 4, 2023

@the Pinnacles

The Pinnacles in Western Australia is a natural wonder located in the Nambung National Park, in the central part of the South Nambung region. The Pinnacles are a landscape consisting of thousands of limestone pillars, ranging in height from a few tens of centimeters to four meters. Thousands of massive limestone columns emerge from a single yellow sand, creating a unique pinnacle desert, with the tallest reaching up to 3.5 meters, each having different shapes – some are low and sharply edged, resembling tombstones.

So, how were these stone formations created?

The limestone material of The Pinnacles comes from the decomposition of shells in the sea, forming sandy deposits rich in calcium carbonate. These sands are carried to the shore by the waves and then transported inland by the wind, creating ancient sand dunes. Three ancient sand dune systems run parallel to Western Australia's coastline, forming an ancient coastal landscape.

Among these sand dune systems, the Spearwood system is the oldest, with sands appearing in yellow or brownish colors. During the rainy season in winter, rainwater, slightly acidic, infiltrates the ground and dissolves some calcium carbonate. In the summer, the dunes dry out, leading to the precipitation of calcium carbonate at the bottom of the dunes. Over time, this accumulation forms hard limestone rocks, also known as Tamala limestone.

At the same time, vegetation growing on the surface of the dunes aids in the formation process of limestone. The vegetation solidifies the dune's surface, accelerating the formation of silicified soil layers and humus layers. The acidic soil layer expedites the leaching process, forming a hard skin on the relatively soft limestone. Plant roots create cracks on the hardened layer, contributing to the formation and preservation of The Pinnacles. When the surface weathering occurs and the soft sand is blown away by the southwest winds or cleared by bushfires, the remaining parts are the hardest limestone formations we see today.

Similar geomorphological features like The Pinnacles can also be found in the southern part of Nambung National Park, as well as near Guilderton, Lake Gnangara, Bibra Lake, and Mandurah.

The Pinnacles are indeed a very unique and stunning geological landscape, attracting countless visitors to come and admire this natural wonder.