A Sea of Parallel Dunes
The Great Sandy Desert contains one of the world's most extensive fields of linear sand dunes. Known as longitudinal or "seif" dunes, they form vast, parallel ridges that stretch across the landscape for tens of kilometers. Individual dunes can reach lengths of 40 to 50 kilometers and rise to heights of around 25 meters. They are spaced with remarkable regularity, typically between 0.5 and 1.5 kilometers apart.
These immense structures are aligned in a consistent west-northwest to east-southeast orientation. This alignment is a direct result of the prevailing winds that have sculpted the region over thousands of years. The anti-cyclonic wind patterns of the subtropical high-pressure system are the primary force behind their formation. Because of their immense size and the partial stabilization by vegetation, the dunes are largely immobile. Their orientation records atmospheric circulation patterns from past millennia, showing ancient climatic conditions.
The entire desert landscape overlies the Canning Basin, a massive geological structure with sedimentary layers up to 15 kilometers thick in some areas. The sand of the dunes is part of the Quaternary sediments that form the basin's uppermost layer.
A Landscape of Red Sand and Spinifex
The characteristic red color of the dunes comes from a thin coating of iron oxide on the individual quartz sand grains. This landscape, is arid but not barren. The dunes and the interdune corridors, known as swales, are largely stabilized by hummock grasslands of spinifex (genera Triodia). These hardy grasses anchor the sand, preventing the dunes from shifting significantly. The swales between the dunes can support different vegetation, including shrubs like Acacia and Grevillea, and sometimes form claypans that hold water after rare rainfall events.
The ecosystem is rich in reptile species, particularly skinks and geckos adapted to the sandy environment. The desert also contains "fairy circles," mysterious barren patches of earth from 2 to 12 meters in diameter, which one theory suggests are created by harvester termites.
Beneath the sand, the Canning Basin holds ancient paleodrainage systems—the remnants of river networks that were active more than 55 million years ago when the Australian continent was situated in a wetter climatic zone. Today, these ancient riverbeds manifest as chains of salt lakes, such as Lake Auld, which only fill with water intermittently.