A shift from drought to extreme rainfall drives a stable landslide to catastrophic failure

The addition of water on or below the earth’s surface generates changes in stress that can trigger both
stable and unstable sliding of landslides and faults. While these sliding behaviours are well-described
by commonly used mechanical models developed from laboratory testing (e.g., critical-state soil
mechanics and rate-and-state friction), less is known about the field-scale environmental conditions or
kinematic behaviours that occur during the transition from stable to unstable sliding. Here we use radar
interferometry (InSAR) and a simple 1D hydrological model to characterize 8 years of stable sliding
of the Mud Creek landslide, California, USA, prior to its rapid acceleration and catastrophic failure on
May 20, 2017. Our results suggest a large increase in pore-fluid pressure occurred during a shift from
historic drought to record rainfall that triggered a large increase in velocity and drove slip localization,
overcoming the stabilizing mechanisms that had previously inhibited landslide acceleration. Given the
predicted increase in precipitation extremes with a warming climate, we expect it to become more
common for landslides to transition from stable to unstable motion, and therefore a better assessment
of this destabilization process is required to prevent loss of life and infrastructure.