Mineralogical Analysis of Selective Melting in Partially Coherent Rockslides: Bridging Solid and Molten Friction

Abstract Frictional shearing along the basal slip surface is the main energy dissipation mechanism in coherent landslides, which undergo little internal deformation during runout. Most landslide bodies, however, deform and break down more or less extensively; thus, only a portion of their potential energy is dissipated through basal shearing. The mineral components of rocks and soils have individual melting temperatures. Therefore, as temperature increases, selective melting will occur in a defined sequence. The product of such melting is termed frictionite. Here, we exploited a sliding block model to investigate the role of selective melting in the evolution of the frictional resistance (and hence mobility) of partially coherent landslides. We recognized three frictional stages, characterized by weakening, strengthening, and melt lubrication. As melting proceeds, a gradual transition from solid friction to viscous flow occurs, which can be modeled in terms of the molten mineral fraction. The chemical composition also evolves and so does its viscosity. Rocks with different mineral proportions (e.g., mafic vs. felsic rocks) will exhibit different frictional evolutions. Our model results are consistent with the recognized role of landslide thickness in defining its mobility. Moreover, the frictional strengthening stage is shown to become irrelevant under high confinement, thereby facilitating higher mobility, or sometimes shifting slip surface if weak layer exists. We also discussed the relevance of some strengthening‐upon‐melting behavior observed at the experimental scale, pointing out the role of the energy conversion coefficient, which is a proxy for landslide coherence.