An evolutionary scheme for morphological classification of Martian gullies

Martian gullies are geologically recent small-scale features characterised by an alcove-channel-apron morphology associated on Earth with liquid water. Since their discovery by Malin and Edgett (1), several theories have been advanced to explain their formation. These typically emphasise either groundwater processes (1, 2) or melting of ground ice or snowpack (3). The former approach has been challenged on the basis of gullies observed on hills and central peaks, where aquifers are unlikely (4). Studies of gullied walls have been undertaken (5), but though morphological classifications of gullies have been proposed (1), they are largely descriptive. This study proposes an evolutionary classification scheme and a pilot study to determine its potential to address controversies in gully formation.