ALBERT

Description: The mobility of landslides on Mars is studied based on a database of 3,118 events. To establish the volume of the landslides for the whole dataset based on the deposit area, a new volume-area relationship based on a representative dataset of 222 landslides is used. Plotting the H/L ratio between fall height H and runout L versus volume, landslide mobility is analyzed and compared with existing empirical relationships for Martian and terrestrial landslides. Analyzing the mobility in terms of normalized residuals, i.e., the relative deviation of the H/L ratio from the dataset best-fit line, mobility is found to depend on both the landslide location on Mars, and landslide typology. This allows us to identify four different types of high mobility (hypermobile) landslides. Three classes of high mobility landslides are associated respectively to meteoroid impact, the Olympus Mons aureoles, and landslides with Toreva-block failure style, and their mobility can be explained by the peculiar flow mechanics. The fourth class includes landslides associated with isolated craters, those in the regions wetted by the putative Oceanus Borealis, and the ones at high latitudes. We suggest that the common factor behind all the hypermobile landslides of this fourth kind is the presence of ice. This is confirmed by our data showing that landslides increase in mobility with latitude. The latitudinal trend mirrors the distribution of ice as detected by radar, neutron probes, and the presence of glacial and layered ejecta morphologies. Because the overall landslide distribution supports the presence of ice-lubricated conditions, two ice lubrication models are presented showing how ice melting within or underneath the landslides could enhance mobility. By proper analysis in terms of apparent friction residuals, we find that the mobility of landslides in Valles Marineris with the largest landslide concentration is lower than average. We explain this circumstance partly from the smaller role of ice in equatorial Valles Marineris, and partly because the collapses from high slope relief imply high-speed impact with the floor valley confinement, loss of momentum, and decrease in mobility. Environmental consequences imply that the present subsurface ice distribution may have been persistent throughout the Amazonian period.