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Show 6 The very rapid formation of depth hoar has been observed, again in the case of new snow on warm, bare ground. Often this phenomenon will precede the above- mentioned formation of air pockets. The structure itself is extremely wet and soft. Crystals are large, 3 to k milimeters; they seldom attain the full cup shape of mature depth hoar, but tend to melt into slush or freeze into an easily crumbled uneven crust layer prior to matur ity. During Santa Ana conditions, or periods of north influence, particularly in early spring, settlement and ablation rates can be extremely high. As much as 50% of the pack can disappear in one day. Free water at ground level is common with this condition. ( See Fig. IV) However, due to the extreme dryness of this type of wind, it can be assumed that some of the moisture from the snow pack is lost to the atmosphere. AVALANCHE FACTORS The picture thus presented is, for the most part, harmonious with that outlined for the Pacific Coast by LaChapelle ( 1965), with the following accentuation according to local observations to date: Avalanche activity is confined almost entirely to direct action, with slides running during, or within k8 hours after each storm. Major contributing factors are raincrust layers or layers of consolidated graupel. Both characteristic ingredients of the local snow layers are caused by the often extreme, sharp rise in temperature following storms. Sun- ball action or direct rain serve as triggers. Old snow layers with persistent high prevailing temperatures as a rule tend to stabilize quickly and settle through metamorphism. Thus |