Gilgai

A gilgai is a small, ephemeral lake formed from a depression in the soil surface in expanding clay soils. Additionally, the term "gilgai" is used to refer to the overall micro-relief in such areas, consisting of mounds and depressions, not just the lakes themselves. The name comes from an Australian Aboriginal word meaning small water hole. These pools are commonly a few metres across and less than 30 cm (12 in) deep, however in some instances they may be several metres deep and up to 100 m (330 ft) across. Gilgais are found worldwide wherever cracking clay soils and pronounced wet and dry seasons are present. Gilgais are also called melonholes, crabholes, hogwallows or puff and shelf formations.