Frictional velocity-weakening in landslides on Earth and on other planetary bodies

Abstract

One of the ultimate goals in landslide hazard assessment is to predict maximum landslide extension and velocity. Despite much work, the physical processes governing energy dissipation during these natural granular flows remain uncertain. Field observations show that large landslides travel over unexpectedly long distances, suggesting low dissipation. Numerical simulations of landslides require a small friction coefficient to reproduce the extension of their deposits. 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. This method uses a constant basal friction coefficient that reproduces the first-order landslide properties. We show that friction decreases with increasing volume or, more fundamentally, with increasing sliding velocity. 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.

Reply to comment by Iverson on “The reduction of friction in long runout landslides as an emergent phenomenon”

“…As previously stated, there is likely a continuum from [Legros, 2002;Howard, 1973;Brunetti et al, 2015;Malin, 1992;Schenk and Bulmer, 1998;Shingareva and Kuzmin, 2001]. Moreover, the mobility of lunar slides is comparable to that of terrestrial slides of similar volume [Lucas et al, 2014]. This suggests that the presence of water in relatively dry terrestrial slides may not significantly contribute to the reduction of friction.…”

“…Another line of evidence supporting the interpretation that friction is reduced throughout the slide mass comes from recent landslide models of Lucas et al [2014]. By including a phenomenological friction weakening rheology, Lucas et al [2014] were able to reproduce the morphology of landslide deposits from the laboratory scale up to the largest long runout landslides.…”

“…However, experiments are currently unable to reproduce long runout behavior for dry slides. Lucas et al [2014] showed that the effective friction of slides is relatively constant for slide volumes below~10 3 m 3 and that μ eff decreases with increasing volume for larger slides. This volume dependence indicates that the reduction of friction of dry slides is an emergent phenomenon.…”

“…By including a phenomenological friction weakening rheology, Lucas et al [2014] were able to reproduce the morphology of landslide deposits from the laboratory scale up to the largest long runout landslides. This friction weakening rheology acts globally and is consistent with initial shearing of the entire landslide mass.…”

“…Analytical models of slides with a coulomb rheology show that μ eff can be estimated using easily measured quantities regarding the initial and final geometry of the slide [Lucas et al, 2014]. A compilation of data from laboratory experiments of dry granular flows and terrestrial landslides shows that μ eff is relatively constant for slide volumes below~10 3 m 3 and that μ eff decreases with increasing volume for larger slides [Lucas et al, 2014].…”