51st Lunar and Planetary Science Conference (2020) 2404.pdf

OBSERVATIONS OF MASS WASTING EVENTS IN THE CERBERUS FOSSAE, MARS. C. M. Dundas1, I. J. Daubar, 1U.S. Geological Survey, Astrogeology Science Center, 2255 N. Gemini Dr., Flagstaff, AZ 86001 ([email protected]), 2Brown University.

Introduction: The Cerberus Fossae are a set of ge- Rockfall tracks are observed at several locations. ologically-young, steep-sided fissures in the Elysium These include both simple falls and large events break- region of Mars, which appear to have been the source of ing into many individual tracks (Fig. 2). floods of both water and lava [e.g., 1–4]. They have also been proposed as the site of recent seismically-triggered mass wasting [5–6]. The latter possibility is of particular interest because the fossae are in the same region as the InSight lander and may be tectonically active [7-8]. This abstract reports on observations of active mass move- ment in and near the Cerberus Fossae using before-and- after comparisons of images acquired by the High Res- olution Imaging Science Experiment (HiRISE) [9]. Observations: Thirty-six locations were analyzed, mostly covering the Cerberus Fossae but also including some nearby craters and massifs. Slope activity of some form was observed at ten of these locations, although in some cases it is minor. The observed mass wasting near the fossae can be divided into three categories: slope streaks [cf. 10], slope lineae, and rockfalls. Slope lineae in the fossae were previously described [11–12]. Recent observations confirm that some of the lineae in the Cer- berus Fossae grow incrementally (Fig. 1), observed by some previous work [11] but not others [12].

Figure 2: Dark rockfall tracks in one of the Cerberus Fossae (HiRISE images ESP_030378_1900 and ESP_059349_1900.)

Additionally, one crater on the Cerberus plains ex- hibited a colorful new flow (Fig. 3) in a poorly-defined gully-like feature. This feature is distinct in color from slope streaks observed in the same crater. Discussion: The features observed here demonstrate that mass wasting processes other than slope lineae and slope streaks are ongoing in the Cerberus Fossae; recent results have also demonstrated this in other equatorial regions of Mars [13–14]. Active slope evolution and surface modification is not restricted to mid- and high- latitude regions with abundant volatiles.

Figure 1: Incremental growth of slope lineae (HiRISE images The present-day occurrence of sporadic new rock- ESP_057516_1965 and ESP_059283_1965.) falls in the Cerberus Fossae indicates that older tracks 51st Lunar and Planetary Science Conference (2020) 2404.pdf

there are not necessarily the result of a handful of large must be low and non-seismic triggers are probably in- seismic events [cf. 5–6]. However, no new examples of volved [e.g., 10, 12, 15, 17-18]. Rockfalls hold more the deeply incised tracks reported there were observed promise for such a comparison; although their orienta- in this study. This may indicate that the incised tracks tions suggest that thermal stresses are important to rock are due to larger, rarer falls. breakdown [19], seismic shaking may be the proximate trigger in many cases. However, confident linkage be- tween a seismic event and an individual rockfall would require tight time constraints that are rarely possible with HiRISE. Acknowledgments: This work was funded by Mars Data Analysis Program NNH16ZDA001N. HiRISE tar- geting was funded by the Mars Reconnaissance Orbiter project. References: [1] Burr D. M. et al. (2002) Icarus, 159, 53-73. [2] Head J. W. et al. (2003) GRL, 30, 1577. [3] Jaeger W. L. et al. (2007) Science, 317, 1709-1711. [4] Morgan G. A. et al. (2013) Science, 340, 607-610. [5] Roberts G. P. et al. (2012) JGR, 117, E02009. [6] Brown J. R. and Roberts G. P. (2019) JGR, 124, 801-822. [7] Banerdt W. B. (2019) EPSC, abstract #1066. [8] Jacob A. et al. (2019) AGU fall meeting, abstract #DI141A- 03. [9] McEwen A. S. et al. (2007) JGR, 112, E05S02. [10] Sullivan R. et al. (2001) JGR, 106, 23607-23633. [11] Runyon K. D. et al. (2012) LPSC, abstract #2072. [12] Stillman D. E. (2018) Dynamic Mars, 51-85. [13] Thomas M. F. et al., Icarus, in press. [14] Dundas C. M. et al. (2019) GRL, 46, 5075-5082. [15] Bhardwaj A et al. (2019) Rev. Geophys., 57. [16] Aharonson O. et al. (2003) JGR, 108, E12, 5138. [17] McEwen A. S. et al. (2011) Science, 333, 740-743. [18] Dundas C. M. et al. (2017) Nature Geosci., 10, 903-907. [19] Tesson P.-A. Figure 3: A) Colorful flow initiating in a poorly-defined gully. et al. (2019) LPSC 50, abstract #2352. B) Slope streaks lower on the same slope. (HiRISE enhanced- color image ESP_042892_1805.)

The colorful flow shown in Fig. 3 presents a surpris- ing contrast with slope streaks observed in the same crater, although some of the streaks show a slightly blu- ish coloration. Although prominent in color, this flow is less distinct than fresh slope streaks in HiRISE broad- band red-filter data. Slope streaks have been attributed to dust avalanches [e.g., 10] although wet origins are still debated [e.g., 15]. The differences between this flow and adjacent slope streaks suggests different dark- ening mechanisms: the colorful flow may incorporate non-dust material. This relatively-blue enhanced color, in this region, is commonly due to basaltic sand. Although any mass-wasting feature could be trig- gered by marsquakes and InSight reports activity asso- ciated with the fossae [9], it is not possible at present to attribute any of these features to seismic effects. The high frequency of slope lineae and slope streak for- mation planet-wide [e.g., 12, 16] makes them poor can- didates for any such effort, since the driving stresses