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Show Interpretation: Chart No. 5 ( Figure 40) This profile was taken in a location near the test area and of similar aspect. To the observer it indicated a situation comparable to that on Chart No. 3, a slab layer of low resistance over a zone of no support. Under explosives, the area avalanched to the ground. Interpretation: Charts Nos. 7 and 8 ( Figures 41 and 42) These profiles illustrate similar conditions in two areas of similar aspect but a number of miles apart. Again we have the situation of two slab layers, each laying over a zone of weakness. In both cases an avalanche was triggered by protective skiing. For Chart No. 7, the fracture penetrated both slab layers but only the upper layer avalanched. The observer considers that the lower layer stabilized in place due to its strong anchorage at the toe of the slope. It was buttressed by the debris from several earlier slides. On Chart No. 8, only the upper layer avalanched at first. Eventually the* lower, high resistance layer did break and carry with it the balance of the snowpack. Interpretation: Figure No. 43 This profile shows the application of the Berthoud Pass technique to an area in a different alpine zone and several hundred miles distant. The profile was taken in a slidepath alongside and similar to a slope which had released a climax type avalanche one month earlier. According to the standards set up by the Berthoud Pass studies, a hazardous situation was indicated. Accordingly the slope was blasted. The outcome was extensive fracturing with stabilization in place. Another profile was taken at the same location approximately one month later. The weak layer and the slab had become homogenous and the profile had assumed the pyramidal shape indicated by the dotted line. Colored Thread Profile Studies ( These studies have been conducted for the winters of 1950- 51 and 1951- 52 by Avalanche Forecaster M. M. Atwater at Alta, Utah, Wasatch National Forest.) The colored thread profile is another method of investigating the nature of the snowpack. The technique has no immediate application to hazard forecasting since the data is not compiled and analyzed until the end of the winter. The objective is to identify the individual strata of an entire winter and study the changes which take place: shrinkage, resistance to vertical penetration, resistance to horizontal penetration, density and metamorphosis of the snow particles ( Figure No. 44). Some very interesting information has been gathered, especially concerning shrinkage in various types of snow. This data promises to supplement and refine eventually the techniques of hazard forecasting for both direct and delayed action avalanches. - 110 - |
