Snow densification during rain

Observations and measurements indicate rain often has a major impact on snow slope stability. Measurements to investigate the effects of wetting of low density, alpine snow were made at Snoqualmie Pass, WA, USA. Results indicate that on first wetting, the densification rate can increase by three orders of magnitude. This initial burst of densification occurs independently of the gravitational load and is probably a result of rapid structural changes and grain rearrangement that occurs when liquid water is first introduced. The rate decreases rapidly with time, although it remains about two orders of magnitude higher than that for dry snow of the same density. The rate of densification decreases as density increases. We assume snow behaves as a linear viscous fluid and that the metamorphic and gravitational components of compaction are additive. A simple model of compaction is derived empirically using the measurements. The model fits the measurements very well, although more experiments are needed to determine the dependence of the model parameters on liquid water content.