Ask an engineer?

Ask an engineer?

Q: How did the Devil’s Marbles get there? 

- Paul, Melbourne

A: Great question! We asked Senior Engineering Geologist Trevor Smith - and he's got the answer!

The Devil’s Marbles are located in the middle of the Northern Territory. Unlike Stonehenge, the marbles, consisting of granite rock, were actually formed exactly where you see them now – 1.7 billion years ago – as a result of molten magma squeezing between sandstone layers. As granite cools and ages, it shrinks and cracks, making horizontal and vertical fractures. Over a very long period of time, the surrounding softer rock layers have washed away – and the granite itself has been eroded by water travelling along those crack lines. With the clay washed away, the boulders have been left exposed. The rock is formed in layers, like an onion, and over time, the edges have then been exposed to a process of chemical weathering (from water and the substances dissolved in it), which peels away the top few layers of the rock to leave it softened and rounded – which is how we see them today.

There are many, many boulders, in an area of approximately 18 square kilometres. The boulders range in size from a mere 50cm across, up to around 6m.

The local Aboriginal name for the rock is Karlwekarlwe or Karlu Karlu – round rocks. Sacred to them as an important dreamtime site, they have many legends and traditions associated with the area.

The area that the rocks are found in is now part of a conservation reserve. It belongs to four local tribes, but is currently under the joint authority of the Aborigines and Parks and Wildlife Rangers. To find out more about it, or to plan a visit, check out the Northern Territory government website.

If you've got a question for one of our engineers or scientists, please contact us via ask@tonkintaylor.co.nz