gilgai Undulating micro-relief of soils which contain large amounts of clay minerals (e.g. montmorillonite) that swell and shrink considerably on wetting and drying, to an extent that may be sufficient to fracture pipelines or move telegraph or fence poles from the vertical. The word is derived from a settlement in Queensland, Australia, where the soils of swelling clays are especially common. See also PATTERNED GROUND.

gilgai The undulating micro-relief of soils which contain large amounts of clay minerals (e.g. montmorillonite) that swell and shrink considerably on wetting and drying, to an extent that may be sufficient to fracture pipelines or move telegraph or fence poles from the vertical. The word is derived from a settlement in Queensland, Australia, where the soils of swelling clays are especially common. See also patterned ground.