Snow densification during rain

Observations and measurements indicate rain often has a major impact on sno w slope stability. Measurements to investigate the effects of wetting of lo w density, alpine snow were made at Snoqualmie Pass, WA, USA. Results indic ate that on first wetting, the densification rate can increase by three ord ers of magnitude. This initial burst of densification occurs independently of the gravitational load and is probably a result of rapid structural chan ges and grain rearrangement that occurs when liquid water is first introduc ed. The rate decreases rapidly with time, although it remains about two ord ers of magnitude higher than that for dry snow of the same density. The rat e of densification decreases as density increases. We assume snow behaves a s a linear viscous fluid and that the metamorphic and gravitational compone nts of compaction are additive. A simple model of compaction is derived emp irically using the measurements. The model fits the measurements very well, although more experiments are needed to determine the dependence of the mo del parameters on liquid water content. (C) 1999 Elsevier Science B.V. All rights reserved.