The slope deformation processes described in the paper, define a typical example of unstable behaviour for a tectonically active chain area in Italy, where slopes are formed of highly tectonized soils and rocks. Monitoring data compared to numerical modelling results show the existence of two interconnected mechanisms of deformation in the slope: a fast shallow mechanism (slump-earthflow) and a deeper and slower deformation process (deep-seated creep). This mechanism is fundamentally due to the poor mechanical properties of the deep soils, which are at yield and therefore undergo significant plastic deformations for even limited changes in loading.