|Above:Gibber plain between Roxby Down and Andamooka|
Left: Angular pieces of gibber from the plain shown above.
Gibber plains are flat areas covered in loose rocks and stones of various sizes the arid and semi-arid parts of Australia. Sturts Stony Desert gets its names from the gibbers covering the surface and there are many other areas of gibber around Australia.
Formation of gibber plains can be traced back to many million years ago in a far wetter, monsoonal climate when heavy rain flushed soluble soil elements out of the soil profile. Most minerals were washed away but silica was redeposited at the surface and acted as cement binding soil particles together. Solar heating baked these particles into a hard siliceous crust known as silcrete duricrust. Once formed, this silcrete duricrust protected the leached ground beneath from rainfall and other erosive forces for millions of years.
Silcrete is hard and resistant to weathering and erosion but the duricrust was, eventually, fractured by earth movement. After the silcrete duricrust was broken, the weakened softer underlay was washed away by rain and flowing water. This removed support from the hard duricrust which then broke up into large pieces. Over time, these pieces of duricrust weathered into smaller pieces forming a rocky pavement.
|Gibber plain north east of Coober Pedy near the Breakaway|
¶ http://www.oz-greetings.com.au/geology/article/23/STURTS--STONY--DESERT - accessed 13 Dec 09.
¶ http://www.encyclopedia.com/doc/1O13-gibberplain.html - accessed 13 Dec 09.
¶ http://www.britannica.com/EBchecked/topic/233137/gibber - accessed 13 Dec 09.