SEASONAL SLUMPS IN JUVENTAE CHASMA, MARS

The contemporary surface of Mars is modified by a variety of active processes such as dust devils, slope streaks, new impact craters, and gullies. Another class of active features that may be modifying the surface of Mars are recurring slope lineae (RSL). RSL are narrow, elongated and dark-albedo surface markings that incrementally grow downslope on steep terrains of Mars. RSL form and grow on warm Sun-facing slopes, and gradually fade and completely disappear when the temperature plummets. The temperature-dependent formation of RSL has led many to hypothesize that volatiles such as brines may play a role in their formation, although dry processes have also recently been proposed. The degree to which RSL may reshape topography is not understood, as large-scale topographic modification by RSL has not been detected in ~30 cm/pixel HiRISE images. The formation of small, dark topographic slumps has been detected on the slopes below active RSL on slopes of Garni Crater and on hills of Juventae Chasma (JC); however, it is unknown if the topographic slumps are caused by RSL activity. Here we describe the observations of nine topographic slumps in JC. These slumps can be up to several meters wide, tens of meters in length and up to a meter in depth. Near their point farthest upslope, the slumps are characterized by topographic depressions due to the removal of materials; near their lowermost point, new materials are deposited in lobes. Due to their resemblance to earthflows, we adopt the term marsflows for these features. The fading timescale of the dark albedo of the slump is rapid (~60 sols) and is comparable to the fading of RSL once they cease growth. Over the course of three Mars years, nine active slumps have been observed in JC, all of which formed in or near the same season (Ls 340-120, mostly southern autumn). Mars Color Imager (MARCI) observations show low-altitude atmospheric obscurations confined within the topography of JC in the seasons when the marsflows form. Further monitoring of this site will help establish if RSL and/or atmospheric events play a role in the creation of contemporary slumps.