The presence of longitudinal ridges documented in long runout landslides across our solar system is commonly associated with the existence of a basal layer of ice. However, their development, the link between their occurrence and the emplacement mechanisms of long runout landslides, and the necessity of a basal ice layer remain poorly understood. Here, we analyse the morphometry of longitudinal ridges of a martian landslide and show that the wavelength of the ridges is 2–3 times the average thickness of the landslide deposit, a unique scaling relationship previously reported in ice-free rapid granular flow experiments. We recognize en-echelon features that we interpret as kinematic indicators, congruent with experimentally-measured transverse velocity gradient. We suggest that longitudinal ridges should not be considered as unequivocal evidence for presence of ice, rather as inevitable features of rapid granular sliding material, that originate from a mechanical instability once a kinematic threshold is surpassed.

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Tectonic pseudotachylytes are solidified frictional melts, formed within faults during co-seismic slip (Maddock, 1983;Sibson, 1975), and are considered to be unambiguous evidence of past earthquakes (Cowan, 1999;Rowe & Griffith, 2015). Despite the clear seismic origin of pseudotachylytes, there has been a long debate regarding the environmental conditions during their formation within fault zones. While some authors argued in favor of a water-deficient environment condition hypothesis for pseudotachylyte formation (Sibson, 1975;Sibson & Toy, 2006), there is a growing body of research pointing toward pseudotachylyte formation in "wet" environments (

On the Moon, mass wasting processes are mainly reported on the steep slopes of impact craters (Kokelaar et al., 2017). These events involve dry granular material, from regolith (sub mm) to boulder sized, and occur in vacuum in the absence of liquid water. These features can reach runout lengths of about 3 km. Recently these specific landslides have been studied in detail, as high-resolution images acquired by the Chandrayaan-1 Terrain Mapping Camera (TMC, 5 m spatial resolution [Kumar & Chowdhury, 2005]) and the Lunar Reconnaissance Orbiter Narrow Angle Camera (LROC NAC, ∼50 cm spatial resolution; Robinson