| To gain further insight into the properties of weak layers composed of precipitation particles(PP weak layer), we analyzed 18 measurement datasets. All analyzed data were collected from avalanche fracture lines or flat sites near avalanche starting zones; these data correspond to notable PP weak layer-related avalanche activities observed in Japan. PP weak layers were found at depths of 6-117 cm, and these layers were 2?22-cm thick. At all study sites, the PP weak layers were composed of large (diameter: 1.0-2.5 mm) rime-less stellar or dendrite planar crystals. The density of the observed layers ranged between 63 and 190 kgm-3. The shear frame index?density relationship of the studied layers resembled that observed by Jamieson and Johnston (2001) rather than observed by Yamanoi and Endo (2002) and Perla et al. (1982). Further analysis of larger datasets obtained from various regions with snow climate is necessary of the properties of weak layers. However, our results suggest that the identification of the types of precipitation particles present in the snowpack under consideration is important for snow stability evaluation and avalanche forecast when weak layers composed of precipitation particles are involved. |
