Reactivation Mechanism of Dormant Earthflows: Insights From the San Benedetto Landslide (Northern Apennines, Italy)

Earthflows are landslides in fine‐grained materials that alternate long dormant phases of very slow movement with short paroxysmal stages of rapid motion. These rapid phases are highly destructive, often causing severe damage to buildings and infrastructure. Despite their impact, the mechanisms controlling earthflow reactivation, the behavior of the remobilized material, and the evolution of the stress–strain field remain poorly understood. We investigate these issues through the 2024 reactivation of the San Benedetto earthflow (Northern Apennines, Italy), a large landslide that experienced two major remobilizations in the past three decades (1994 and 2024). The 2024 event was initiated by a large slide in the upper slope, which triggered reactivation of the dormant earthflow. The process was monitored from the first day, yielding detailed observations of displacement and geomorphic evolution. The data show that large‐scale movement was preceded by a rapidly advancing deformation front that propagated about three times faster than the earthflow body itself. Once mobilized, the earthflow underwent displacement exceeding 700 m, producing a longitudinal shortening of 70%–90%. To interpret these findings, we develop a simplified mechanical model in which the dormant earthflow is represented as an elastic layer resting on a rigid–plastic basal slip surface. The model indicates that the load generated by the initial slide was sufficient to reactivate the entire slip surface and highlights the key role of lateral confinement in shaping the spatial distribution of displacement along the earthflow.