On the mobility of large

A new landslide mobility parameter that takes the friction angle into account can shed new light into the dynamics of large Martian landslides. Introduction: Landslide morphologies have been identified on Mars [1-2]. Some similarities between experiments on dry granular spreading and Large Martian Landslides (LML) convey to conlude on dry conditions [3]. However, normalized runout on Mars is twice as large as those observed in laboratory. Numerical simulations on theoretical 2D and real 3D topographies reconstructed from remote sensing data show that slope effects significantly reduce the discrepancy between experimental results and Martian observations [4]. However, topography effects are not strong enough to explain the high mobility of Martian landslides, which requires a very small friction angle (δ < 10°), much smaller than required in dry granular spreading simulations (δ = 32°) [4]. As a result, physical processes such as air cushioning or lubrication by a fluid phase should play a key role in the dynamics of Martian landslides. We investigate landslide mechanics using a new mobility parameter [4] that makes it possible to characterize the flow dynamics regardless of the geometry of the released mass and of the underlying topography. Morphometric parameters of LML: Quantin et al. [5] have performed a systematic geomorphology analysis of VM landslides using THEMIS, MOC and MOLA data sets. More recently, Lajeunesse et al. [3] have performed a morphometric analysis of these landslides. From these studies, some landslide morphometric parameters can be defined (fig. 1). Morphometric Survey: From THEMIS, MOLA and MOC data available from PDS [6], we performed a morphometric survey using these parameters on five large Maritan landslides (fig. 2). Mobility of Martian landslides: The classical mobility is defined as: It is volume-dependant. We define instead a new mobility parameter m’e, which reads [4]: where θ is the bottom slope, and α =1.24 a dimensionless parameter introduced by [7]. The mobility parameter is independent of the initial landslide volume, its aspect ratio, and the underlying topography. This mobility m’e is thus a function of the friction angle δ. We calculate m’e for the following landslides: Landslides Mobility (m’e) δ (°) Ophir 5.8 9.8 Candor 5.6 9.9