The great diversity of natural gravitational flows in terms of volumes involved (from a few cubic metres to hundreds of cubic kilometres), flowing materials (for example, soil, clay, rocks, water ice and mixtures of different materials with or without the presence of a fluid phase such as gas or water), environment (for example, different gravitational acceleration on different planetary bodies, underlying topography), triggering mechanisms (seismic, volcanic, hydrological and climatic external forcing) and physical processes involved during the flow (for example, fragmentation 2 and erosion/deposition 3, 4) hinder a unified view of these phenomena. Moreover, catastrophic landslides constitute a significant hazard for life and property. On Earth these mass wasting processes feed rivers with solid materials and thus participate in the evolution of the landscape. They have also been observed on other planetary bodies of our Solar System, from the interior planets to the icy moons of Saturn as well as small bodies such as the asteroid Vesta 1. Inspired by frictional weakening mechanisms thought to operate during earthquakes, we propose an empirical velocity-weakening friction law under a unifying phenomenological framework applicable to small and large landslides observed on Earth and beyond.Īvalanches, debris flows and landslides are key components of mass transport at the surface of the Earth. We show that friction decreases with increasing volume or, more fundamentally, with increasing sliding velocity. This method uses a constant basal friction coefficient that reproduces the first-order landslide properties. Here, based on analytical and numerical solutions for granular flows constrained by remote-sensing observations, we develop a consistent method to estimate the effective friction coefficient of landslides. Numerical simulations of landslides require a small friction coefficient to reproduce the extension of their deposits.
Field observations show that large landslides travel over unexpectedly long distances, suggesting low dissipation. Despite much work, the physical processes governing energy dissipation during these natural granular flows remain uncertain. One of the ultimate goals in landslide hazard assessment is to predict maximum landslide extension and velocity.
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