Devil’s Marbles or Karlu Karlu, as they are known by the local Warumungu Aboriginals, are a collection of massive granite boulders strewn across a shallow valley, 100 kilometers south of Tennant Creek in the Northern Territory, Australia. They are one of the most widely recognized symbols of Australia’s outback.

Formed by erosion over millions of years, the Devil’s Marbles are made of granite with sizes varying from 50 centimeters up to six meters across. Some of the boulders are naturally but precariously balanced atop one another or on larger rock formations, while others have been split cleanly down the middle. Although they appear to have been carefully placed or perhaps brought here by flood or glaciers from distant places, these boulders actually formed on the ground they stand by erosion of rock that reached the surface from below.

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The Devils Marbles started out, many million years ago, when an upsurge of molten rock penetrated the ground from below, spread out and settled into a solid layer within the Earth's crust. After some time, tectonic forces caused folding of the Earth's crust in the area, which lifted the granite causing it to fracture into big, square blocks. Weathering by water and wind rounded off the edges and turned them into smooth boulders that we see today.

Extreme temperature differences between day and night in the arid desert region where the reserve is located generates immense stress on these boulders, causing them to repeatedly expand and contract. Some of the rocks eventually crack completely in half.

The Devils Marbles have great significance for the Aboriginal people, and are protected under the Northern Territory Aboriginal Sacred Sites Act. In the Aboriginal mythology the Devils Marbles are the eggs of the rainbow serpent, and many "dreamtime" stories and traditions of the Warumungu, Kaytetye and Alyawarre Aboriginal people are linked with this area.

According to one story, 'Arrange', the Devil Man, while walking through the area, made a hair-string belt, a type of traditional adornment, worn only by initiated Aboriginal men. As he was twirling the hair to make strings, he dropped clusters of hair on the ground which turned into the big red boulders. Arrange finally returned to his place of origin, a hill called Ayleparrarntenhe, where the legend says he still lives today.

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Sources: Wikipedia / Australia.com / Outback Australia Travel Guide