Forecasting the deformation behavior of deep-seated rock slides in the surroundings of large dam reservoirs requires an understanding of the groundwater situation, the kinematics, the rock mass and shear zone strength as well as in-situ stress conditions. In order to enhance the understanding of the deformation and failure mechanisms of deep-seated rock slides the focus of this study is placed on the impact of the rock slide geometry on the stability evolution during first time impoundment. In particular, the geometry of the rock slide toe and the kinematic rock slide type are considered as key factors regarding the ability of self-stabilization. By means of the limit equilibrium method the effect of reservoir filling on the change of the factor of safety is demonstrated. Furthermore, an outlook of a numerical modelling study is presented where the extent of the rock slide displacements related to changes in the reservoir level is examined.