Landslides are natural hazards occurring in response to triggers of different origins, which can act with different intensities and durations. Despite the variety of conditions that cause a landslide, the analysis of landslide inventories has shown that landslide events associated with different triggers can be characterized by the same probability distribution. We studied a cellular automaton, able to reproduce the landslide frequency-size distributions from catalogues. From the comparison between our synthetic probability distribution and the landslide area probability distribution of three landslide inventories, we estimated the typical size of a single cell of our cellular automaton model to be from 35–100 m², which is important information if we are interested in monitoring a test area. To determine the probability of occurrence of a landslide of size s, we show that it is crucial to get information about the rate at which the system is approaching instability rather than the nature of the trigger. By varying such a driving rate, we find how the probability distribution changes and, in correspondence, how the size and the lifetime of the most probable events evolve. We also introduce a landslide-event magnitude scale based on the driving rate. Large values of the proposed intensity scale are related to landslide events with a fast approach to instability in a long distance of time, while small values are related to landslide events close together in time and approaching instability slowly.