Mass movement reconstruction and boulder size-frequency distribution of the Simud Vallis landslide, Mars

<p>We study a young (~ 4.5 Ma), 3.4 km long landslide located in the floor of Simud Vallis, a large outflow channel that together with Tiu Vallis once connected the Valles Marineris with the Chryse Planitia on Mars (1). Multiple teardrop-shaped islands are present on Simud Vallis&#8217; floor, all elongated in the S&#8211;N direction of the flow (2) that incised the Mid-Noachian plateau (3). The Simud Vallis (SV) landslide is located on the western side of one of such landforms. It is characterized by numerous boulders on its deposits (4). By making use of the 2 m-scale HiRISE DEM of (4) we reconstruct the terrain surface before the SV landslide. We thereby estimate the release and deposition heights and volumes related to the rotational slide of the landslide, called <em>stage 1</em>, and of the subsequent flow, called <em>stage 2</em>. Using the <em>r.avaflow </em>software (5) we simulate the mass movement of stage 2 and obtain simulated deposits that are comparable to the current landslide deposit in terms of both horizontal extent and thickness (6). Through two 0.25 m-scale HiRISE images we identify and manually count <em>></em>130,000 boulders that are located along the landslide, deriving their size-frequency distribution and spatial density per unit area for boulders with an equivalent diameter &#8805;1.75 m. Our analyses (6) shows that the distribution is of a Weibull-type (7), which commonly results from sequential fragmentation and it is often used to describe the particle distribution derived from grinding experiments (8,9). This suggests that the rocky constituents of the SV landslide fractured and fragmented progressively during the course of the mass movement, consistent with our proposed two-stage model of landslide motion.</p><p><strong>References: </strong></p><p><strong>&#160;</strong>(1) Pajola, M. et al., 2016. Icarus, 268, 355. (2) Carr, M.H. & Clow, G.D., 1981. Icarus, 48 (1), 91. (3) Tanaka, K.L. et al., 2014. US Geological Survey. (4) Guimpier, A., et al., 2021. PSS, 206, 105303. (5) Mergili, M., et al., 2017. Geosci. Model Dev. 10, 553. (6) Pajola, M. et al., 2022. Icarus, 375, 114850. (7) Weibull, W., 1951. J. Appl. Mech., 18, 837. (8) Brown, W.K. & Wohletz, K.H., 1995. J. Appl. Phys. 78, 2758. (9) Turcotte, D.L., 1997. Cambridge University Press, Cambridge.</p>