That process is then exaggerated as the depressions hold water and thus become wetter and swell more than the mounds, causing even greater shrinkage and cracking.
Each cycle of swelling, shrinkage and cracking becomes more exaggerated and the landscape eventually becomes covered by a repeated pattern of mounds and depressions.
Australia has an abundance of cracking clay soils and large areas dominated by pronounced wet and dry seasons, providing ideal circumstances for gilgais to form.
[1] Gilgais are structurally similar to the patterned ground of frigid regions, but periglacial soil polygons are formed instead, by repeated freeze-thaw cycles.
The movement of soil associated with gilgai formation damages infrastructure, including building foundations, roads and railway lines, and the undulations interfere with crop harvesting.