A comparison of semiarid and subhumid terrestrial gullies with gullies on Mars: Implications for Martian gully erosion

- Terrestrial gullies provide a benchmark to compare Martian gully forms against.
- Gully formation is not necessarily restricted to a single process.
- Constant Martian gully slopes suggest gullies have not eroded to underlying bedrock.
- Interpretation of gully forms should be placed in context of local environments.

Comparison of Martian hillside gullies with terrestrial analogues is a productive method for gaining an understanding of how surface processes operate on Mars and on Earth as well as their similarities and differences. Here we compare gullies within a semiarid region of Island Lagoon near Woomera, Australia, and periglacial gullies located at Pasture Hill, New Zealand, with the Martian gullies in Noachis Terra. We discovered that fluvial processes dominate erosion at the terrestrial sites, though in different forms. Concentration of overland flow and the presence of a resistant cap rock have played a key role in the location and shape of the Island Lagoon gullies. The presence of steeper slopes and a greater abundance of volatiles such as water, frost, and snowmelt at Pasture Hill have helped carve channels equivalent in size to the Martian gullies; and the interaction of frost, dry flows, snowmelt, and debris flows has led to a complex regime of gully erosion and deposition. The observation of similar features on Mars suggests that Martian gully formation is not necessarily restricted to a single process. In addition, gully slopes are closely related to those of their host escarpment as well as the thickness of erodible material and presence of bedrock. Traditional indicators of water-related activity such as slope and sinuosity need to be placed into the context of the environment of the study site.