The Geomorphology of Gnammas (weathering pits) of Northwestern Eyre Peninsula, South Australia: Typology, Influence of Haloclasty and Origins

Abstract

Gnammas on Eyre Peninsula classify as being either pits, pans or armchair pans. Pit gnammas are relatively deep (depth: diameter > 0.2), usually formed by weathering on a hemispherical front and occur anywhere on a rock outcrop. Subtypes include bowls, canoes, armchair pits and plunge pools: this latter type originate by water evorsion. Pan gnammas occur only on flat surfaces, commencing by horizontal weathering along surface laminations, but further incision is by hemispherical and water-layer weathering. They are shallow petri dish in profile with depth:diameter ratios usuallyδ(incison:depth ratio) are unique for each population of gnammas and is influenced by haloclasty.