Strength fluctuations occasionally induce band arrest (first dashed line in Fig. 2(b)) and/or intermittent band propagation, as also observed experimentally. Neither in the simulations nor in the experiments do we see a strong influence of the different band propagation modes on the overall shape of the force-displacement curves. Varying the strain rate by two orders of magnitude, we see a transition between qualitatively different types of spatio-temporal deformation patterns (Fig. 3) depending on the value of the product ˙ e$_{ext}$τ . For ˙ e$_{ext}$τ ≫ 1 , we find a single compaction band followed by homogeneous deformation, a behavior that is typical for solid foams [9]. For ˙ e$_{ext}$τ = 1 we see first one secondary band and then, at even lower strain rates, a procession of bands similar to those observed in our experiments (see also the discussion of stability criteria in the Supplementary Material). We have for the first time demonstrated that the irreversible deformation of snow may proceed in an intrinsically inhomogeneous manner characterized by the repeated nucleation and propagation of localized deformation bands. We could relate this phenomenon to the competition between structural softening under deformation, and age hardening due to rapid sintering processes which restore strength over time. Our findings clearly demonstrate the necessity to investigate and account for strain localization phenomena even when considering initially homogeneous snow samples under homogeneous loads. If shear softening outweights strengthening due to densification, unstable deformation accompanied by spatio-temporal strain 5 Discussion and Conclusions 9 Figure 3: Strain pattern evolution for different imposed strain rates, compressive strain profiles are plotted as a function of the position along the compression axis (the top of the sample is at the left of the graphs); adjacent profiles differ by equal total strain (time) increments. (a) ˙ e$_{ext}$τ = 10 , (b) ˙ e$_{ext}$τ = 1 , (c) ˙ e$_{ext}$τ = 0 . 1 , for other parameters see text.