Gilgai

A gilgai is a small, ephemeral lake formed from a surface depression in expanding clay soils. Gilgai is also used to refer to the overall micro-relief in such areas, consisting of mounds and depressions. 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 reach 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".