An analysis of the effects of creep on the development of a deep-seated gravitational slope deformation (DSGSD), carried out by numerical modelling, is described. The slope rock mass evolution has been simulated applying different creep rheological models. The studied DSGSD is located in the Central Italian Alps (Val S. Giacomo). It is characterised by three main scarps, different sets of tensile trenches, and counterscarps, mapped during a detailed geomorphological survey. The mechanical behaviour of the rock masses, in terms of elasto-plastic parameters, has been defined on the base of laboratory and in situ tests. In order to simulate this instability process, a stress-strain-time numerical modelling has been performed by a finite-difference numerical code (Fast Lagrangian Analysis of Continua-FLAC). The effects of different constitutive model laws have been considered: the visco-elastic Maxwell model; the visco-elastic Burger model and the elasto-visco-plastic Burger model. The modelling has been performed simulating the melting of the ancient glacier, starting from its maximum load. Because of the difficulty to determine rock mass creep parameters, for each of the rheological models, a sensitivity analysis has been performed, varying the physical-mechanical properties. The visco-elasto-plastic model allows to underline the formation of shear surface showing a depth and a shape in good agreement with the morphologic features of the slope. The only action of unloading due to glacier melting seems to be insufficient to generate deep critical surfaces which can be related with the formation of the DSGSD.
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