The presence of gullies on sand dunes is rare on Earth, and their discoveries on Mars and the origin as well as mechanical properties of fluid necessary to the formation of gullies remains currently misunderstood. This study focuses on morphology of gullies over the Russell megadune (54.5°S; 12.7°E). The aim of this study is to better constrain the origin as well as the mechanical properties of the fluid involved into the debris flows. A new HiRISE DTM allowed to better characterize 3D geometry of these morphologies. It makes it possible to measure mass balance for one gully and estimate the eroded and deposited volume. It allows us also to estimate erosion and sedimentation rates along the channel. A series of cross-sections on a gully allowed us to estimate flow velocities, flow discharge and physical parameters such as viscosity, Reynolds number and yield strength (Fig. 1). Based on terrestrial methods ([1], [2], [3], [4]), this approach aims to understand the flow dynamic necessary for the formation of gullies on Martian dunes. Finally, we discuss a model of formation for the Russell's gullies under a periglacial environment.