Formation and strengthening of layers of dry faceted crystals above artificial melt–freeze crusts from overburden stress in a controlled environment

Abstract

Layers of faceted crystals were grown from naturally fallen snow above wet snow layers in a temperature-controlled laboratory. Static loads were then applied to the weak layers to represent overburden snow. Eleven experiments with constant loads were analyzed, equivalent to 260 to 1500 Pa of overburden stress. The density of the slab above the weak layer increased with time, following a power law relationship with an average exponent of 0.10. Shear strength of the weak layer increased with time for all experiments, also following a power law relationship. Early-time rates of strength gain averaged 250 Pa·day−1 for the constant-load experiments over the first 3–5 days, decreasing to an average of <1 Pa·day−1 after approximately 30 days. Exponents for the power law relationships ranged between 0.09 and 0.35 with an average of 0.26 ± 0.08. Sintering was likely the dominant process for strength gain, although densification probably contributed as well. Three experiments were conducted in which the overburden was increased in stages; these exhibited an average strength gain rate of 270 Pa·day−1 over 4–8 days with approximately linear relationships, highlighting the importance of cumulative snowfall for layer strength gain.