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Show commander should have the abilities, sharpened by experience, to steer the rescue operation towards its greatest probability of success. 2.2 Establishing the Victim's Most Probable Location In many respects a moving avalanche resembles a fluid. A human body, with a higher density than the flowing snow, would be expected to sink deeper and deeper into the avalanche. Many complex factors obscure this simple model. Turbulence, the influence of terrain, and the victim's own efforts all interact to determine the final burial position. These same factors can also increase the victim's lateral motion and make more uncertain his f inal pos it ion. Although there are possible mechanisms to deposit an avalanche victim in unlikely spots, the study of a large number of case histories leads to the following generalities: 1. The majority of buried victims are carried to the place of greatest deposit ion- usually the toe of the slide. 2. If two points of the victim's trajectory can be established ( see Section 2.1), a high probability exists that the victim will be near the downhill flow line passing through these two points. See Figure 12. 3. Any terrain features which catch and hold avalanche snow are also apt to catch a victim ( Figure 13). 4. If an avalanche follows a wandering gulley, all bends which show deposition are likely burial points ( Figure 14). The likelihood of a victim being buried at a particular gulley bend is proportional to the amount of avalanche debris deposited there. 5. Vegetation, rocks and other obstacles act as snares. The victim tends to be retained above the obstacle. Obstacles in the avalanche path may also simply delay the victim's motion, leading to final burial somewhere downstream from the obstacle. 6. Maximum speed of the flowing snow occurs at the avalanche center. Friction reduces flow velocity along the edges. The closer the victim's trajectory is to the center of the slide, the greater may be his expected burial depth. 7. Efforts of the victim to extricate by vigorous motion and " swimming" definitely minimize burial depth. Conversely^ the limp body of an unconscious victim is apt to be buried deep. An occasional exception to the above rules is emphasized: The victim may not be buried. In a wild Colorado slide, a fortunate survivor was hurled 10 feet in the air by wind blast and thrown to safety. There are sadder examples of victims that are thrown from avalanches or somehow manage to 32 |