Natural dry-snow slab avalanches start with a failure within a weak snow layer. In order to understand the mechanical behaviour and the failure mechanism, we performed loading experiments with homogeneous and layered snow samples under controlled conditions in a cold laboratory. For simulating loading conditions similar to the natural snow pack, we designed and built an apparatus where a snow sample can be tilted by a ‘slope angle’ and is loaded via the gravitational force. The deformation within the snow sample was measured optically with a pattern recognition algorithm. Shortly before macroscopic failure (breaking of the whole sample) we observed a concentration of deformation (softening) within the weak layer. Additionally, we measure acoustic emissions during the shear experiments to quantify the microscopic failure (breaking of bonds) in the snow sample before the complete failure. Our results support the assumption that the dominating mechanisms for snow deformation are the competing processes of breaking and sintering of bonds between grains.