Fragmentation can occur in rapid solid mass movements due to different controlling factors. In particular, here we consider the initial state of stress, rapid unloading, shearing of highly stressed grain chains and extremely rapid loadings. The last two cases could also be described as dynamic fragmentation, while the first two are more typical of instability phenomena. In this contribution, we present a series of simulations by Discrete Element Method (DEM) for a simple block and slope geometry, where a particle agglomerate of prismatic shape is released along a sliding plane and subsequently collides onto a flat horizontal plane at a sharp kink point. These conditions have been chosen because two sets of experiments with the same settings (Bowman et al. 2010) are available in the literature and resemble simplified natural geometries. In this study, we analyze how dynamic fragmentation occurs in the numerical model and the modes of failure for different rock blocks. The rock fragmentation occurs mainly in the lower part of the rock block after direct impacts with the ground floor, producing several small fragments. The upper part of rock block suffers little influence from the impacts, creating relatively large fragments. Rock masses with many initial weak zones (e.g. fractured or highly weathered rock) exhibit very poor performance of integrity, as represented by their short final runout distances, large breakage ratios, small fragment mass ratios and low final energy.