| OCR Text |
Show Terrain Analysis In order to get a complete picture, the avalanche hazard in any area must be viewed from both the administrative and the technical angles. The administrative standpoint reveals it as divided into three sections. At Alta these divisions are quite distinct and probably would be so anywhere. The traffic area-highway and parking-is one. The lift-served ski area is a second. By "lift-served11 is meant those slopes which the skiers can reach from the lift without climbing on foot. Where touring slopes overhang heavily used runs they are supervised as part of the lift-served area. The touring area adjoins the lift-served. Improvements such as lifts, lodges, and shelters tie in with the divisions they adjoin, lodges generally with the traffic area, lifts with the ski area. Each division has its own special problems. Use of the area, both numbers and distribution, is an important factor. Alta, for example, is a heavily used area compact in form* The close control necessary in the lift-served - division is much easier than it would be if the terrain favored wide distribution of the skiers. The avalanche hazard is concentrated, too. This probably had much to do with causing the high loss of life during mining days when there was no attempt at supervision. With a safety organization functioning, it is actually an advantage. For if the hazard is more severe it is also easier to keep under control. From the technical standpoint, avalanche hazard falls into two divisions J terrain and climate. Without suitable conditions of grade, shape, and surface of the land, there are no ^tvalanches. The most important of these factors is grade. Authorities agree that slope angles of 25° or more are avalanche favorable. Experience at Alta indicates that in this area at least, the critical grade is somewhat sharper; from 30° on up, v/ith the easier slopes becoming involved only when disturbed by snow moving down from higher and steeper locations. The size possible However, momentum with the equals ^ of an avalanche slope has an obvious part to play, increasing the weight and violence of a slide in proportion to its dimensions. a slide of great width descending a short slope will have less than a narrower one on a very long slope. This is in accordance formula so many automobile drivers forget until too late: Energy mass x velocity2, E » -|MV . It is axiomatic that convex slopes are more dangerous than concave because snow settling on a surface that bulges is under a stretching tension. The avalanche habit of fracturing at the exact point where the curve of a convex slope is sharpest has often been noted. At Alta it is our experience that shape, convex or concave, is a minor detail compared to angle and size. For the ski mountaineer, the shape of a slope may indicate the probable fracture point of an avalanche and so assist him in selecting his route. The snow ranger is more concerned with when and how big than exactly where. All the infinitely varied features of a mountainous terrain are important in the analysis of avalanche hazard. Cliffs are too steep to accumulate snow themselves. However, if water veins exist they are apt to release |
