The terms 'stony downs' or 'gibber plains' are used to describe desert pavement in Australia. Similar features are called reg (western Sahara), serir (eastern Sahara), or saï (central Asia). It is a desert surface covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size. Desert varnish can form on the exposed surface rocks over time. In the Dharuk aboriginal language, “gibber” means stone or pebble.
Several theories have been proposed for the formation of desert pavements.
A common theory suggests desert pavement form through the gradual removal of sand, dust and other fine-grained material by the wind and intermittent rain, leaving the larger fragments behind. The removal of small particles by wind does not continue indefinitely, because once the pavement forms, it acts as a barrier to resist further erosion.
Another theory proposes that desert pavements form from the shrink/swell properties of the clay substrate underneath the pavement; when precipitation is absorbed by clay it causes it to expand, and when it dries it cracks along planes of weakness. Over time, this geomorphic action transports small pebbles to the surface.
A third theory is that stone pavements are born at the surface. While the stones remain on the surface due to heave, deposition of windblown dust must build up the soil beneath that pavement.
You will need to examine the desert pavement at two locations 20km apart and report answers to the following questions. The listed coordinates are the western location. There is reference waypoint for the eastern location. Please plan your journey if you are travelling east to west.
- What is the colour of the gibbers at the western site?
- What is the colour of the gibbers at the eastern site?
- What do you think has caused the colour variation?
- Which formation theory do you think would be the most appropriate at the two locations?
References: Wikipedia, Australian National Botanic Gardens, SA History Hub