Mars: Northern hemisphere slopes and slope distributions

We investigate slope distributions in the northern hemisphere of Mars from topographic profiles collected by the Mars Orbiter Laser Altimeter. Analysi s of the region from about 12 degrees S to 82 degrees N, over diverse geolo gic units, indicates that the range of regional-scale slopes is small, gene rally < 3 degrees. Surface smoothness is most distinctive in the vast north ern hemisphere plains, where slopes are typically < 1 degrees. Amazonis Pla nitia is particularly remarkable in its smoothness, exhibiting an rms varia tion in topography of < 2 m over a 100-km baseline. This relative smoothnes s is still present when compared with other sampled areas of the Martian no rthern hemisphere and with volcanically resurfaced terrains elsewhere in th e solar system. Planetary surfaces of large areal extent that are most comp arable to Amazonis in terms of rms elevation variation over long baselines are depositional in origin and include terrestrial oceanic abyssal plains a nd certain sedimentary basins. Slopes across the Valles Marineris canyon sy stem show that the upper portion of the walls are significantly and consist ently steeper than the lower walls, characteristic of extensive mass wastin g. The observed long-runout is consistent with a high-energy collapsed flow . In the neighboring Noctis Labyrinthus canyons the duality between the upp er and lower walls is reduced, and indicates a lower energy modificational history and/or greater cohesion of wall rock.