Karlu Karlu / Devil's Marbles

Karlu Karlu, also known as the Devil's Marbles, is a cluster of large, rounded granite boulders scattered across a shallow valley in the Northern Territory of Australia, formed from a granite body that crystallized deep underground and was later exposed by the erosion of overlying rock, exposing the granite to weathering along a natural grid of horizontal and vertical joints. Groundwater weathering rounded the sharp edges of the resulting rectangular blocks while they were still buried beneath the soil, a process called spheroidal weathering, and once exposed at the surface after the surrounding softer material eroded away, some boulders remained precariously balanced or split cleanly in two, continuing to be shaped today by temperature-driven expansion and contraction and by wind erosion. The formation is deeply significant to several Aboriginal groups of the region, for whom it is associated with ancestral creation stories, and its name, Karlu Karlu, is now used as its official title alongside the earlier settler name.