OCR Text |
Show 2 density range. Laboratory experiments on fresh snow are difficult to set up, hence the development of " in situ" experimental techniques are necessary. Two problems are encountered in the setting up of consistent " in situ" experiments. Figure 1. shows the first problem: Property and structure variation in the z- direction. To solve the first problem requires gathering data at appropriate A z intervals. The second problem is property and structure variation in the x and y directions. The solution of the second problem involves the choice of a suitable study area, free of local wind anomolies, and the statistical design of the experiment to account for X and Y data variations. The drop cone penetrometer The Haefeli ram penetrometer is a convenient device for measuring the strength of the snow pack. In the Haefeli method, an impact energy is imparted to the ram and the corresponding penetration is noted. From these data, strength as a function of z can be calculated for the snow profile. These strength measurements are of great value to the avalanche forecaster in evaluating climax and deep slab hazards. However, even if the Haefeli ram is set gently on a fresh layer of snow, its narrow head may exert a pressure on an order of magnitude greater than the resistive pressure of the snow. At the Alta Avalanche Study Center an instrument, similar in operation to the Haefeli penetrometer, was developed. This instrument, capable of measuring the strength profile of a soft slab, is the drop cone penetrometer. Previous models of this instrument have had a successful history of providing consistent fresh snow data.] ' 2' 3 The sequence of operation for the Alta model ( Figure 2) is as follows: The instrument rests on the snow, supported by its flange in a level position. The |