The Simpson Desert is a large area of dry, red sandy plain and dunes in Northern Territory, South Australia and Queensland in central Australia. It is the fourth largest Australian desert, with an area of 176,500 km² (68,100 sq mi).
The desert is underlain by the Great Artesian Basin, one of the largest inland drainage areas in the world. Water from the basin rises to the surface at numerous natural springs, including Dalhousie Springs, and at bores drilled along stock routes, or during petroleum exploration. As a result of exploitation by such bores, the flow of water to springs has been steadily decreasing in recent years.
The Simpson Desert is an erg which contains the world's longest parallel sand dunes. These north-south oriented dunes are static, held in position by vegetation. They vary in height from 3 metres in the west to around 30 metres on the eastern side. The largest and most famous dune, Nappanerica, or more popularly Big Red (named by Simpson Desert traveller Dennis Bartell), is 40 metres in height.
The explorer Charles Sturt, who visited the region from 1844–1846, was the first European to see the desert, but it was not until 1936 that Ted Colson became the first white person to cross it in its entirety. The name Simpson Desert was coined by Cecil Madigan, after Alfred Allen Simpson, an Australian philanthropist, geographer, and president of the South Australian branch of the Royal Geographical Society of Australasia. In 2008, Belgian explorer Louis-Philippe Loncke became the first person to cross on foot and completely unsupported the length of the Simpson desert, which was North to South and passing through its geographical center. In 1967, the Queensland Government established the Simpson Desert National Park.