Present-day development of gully-channel sinuosity by carbon dioxide gas supported flows on Mars.

Martian gullies have been widely studied, but their formation mechanism is still under debate. Their channels generally trend straight downslope, but some display sinuosity. Seasonally active gullies are common on sand dunes and their channels have been reported to develop sinuosity. Here, we perform a detailed analysis of a gully on a dune within Matara Crater (49.5°S; 34.9°E) where development of channel sinuosity has taken place over 5 martian years (MY29-33) of observation. This study was performed using HiRISE images, HiRISE elevation data, spectroscopic CRISM data and a 1D GCM for surface temperature modelling. The morphological evolution of the gully suggests a significant seasonal contribution of fluid. Each year we observed material collapse and accumulation in the alcove, followed by transport events during which lateral migration and extension of the channel occur together with growth of the debris apron. Over one martian year, the debris apron propagated by almost 140 m from an initial length of 800 m. These transport events occur in the middle of winter when CO 2 frost is still present and are contemporaneous with the beginning of the defrosting. We propose that the activity and the sinuosity development in the gully could be explained by: 1) a flow composed of sand and CO 2 gas, producing morphologies similar to those in hyper-concentrated flows on Earth and 2) contribution of material from alternating of the alcove source location. • Detailed analysis of a dune-gully where development of channel sinuosity has taken place over 5 martian years. • The morphological evolution of the gully suggests a significant seasonal contribution of fluid. • Transport events on the gully occur in the middle of winter when CO 2 frost is still present. • The activity and development of sinuosity in the gully could be explained by a flow composed of sand and CO 2 gas. • Material from alternating source locations contributes to the gully activity. [ABSTRACT FROM AUTHOR]