The Devil’s Marbles

by Deb on January 31, 2011

Devil's Marbles

One thing Central Australia excels at, along with desert and flies, is enormous rock formations.  There’s Uluru (Ayers Rock), Kata Tjuta (the Olgas) and just south of me there are the Devil’s Marbles, or Karlu Karlu.  They’re not as well known as the other two, but similarly fascinating.

Long ago a pocket of magma bubbled up deep underground then cooled to form granite.  It was under extreme pressure from the layers of sandstone on top of it.  Over millions of years as the earth twisted the granite was brought closer to the surface, the pressure on it lessened and it expanded, causing cracks that formed enormous cubes of stone.

Devil's marbles

Water started filtering down through the cracks and enlarging and rounding them.  As they came to the surface it has accelerated with both mechanical and chemical weathering.  Mechanical weathering is physical, the rubbing of stone by wind or water.  Chemical weathering is when water and temperature cause reactions that loosen and crack off parts of the stone.  One important type of weathering is called solarisation.  In the desert there can be extremes of temperature over 24 hours, with very hot days giving way to freezing nights.  This makes the rocks expand and contract relatively quickly and can crack them in half, as shown in two rocks here.

cracks

There are almost certainly examples of weathering around you, even if they aren’t this dramatic.  Buildings weather too!  Have a look around to see if you can find them.

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