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Show skiing. On 15 January, the snow ranger broke several ribs, and it was necessary for local ski instructors to check the slopes. These two instructors had previously worked with the ranger on avalanche control. On the 17th, the storm had cleared, and after the rest of the area was checked out, a charge was placed high on the Upper North Glade slope. ( The shot point may have been slightly higher than it should have been.) Extensive fracturing resulted, but nothing slid. The team traversed across the upper slope and worked their way down, checking several smaller slopes. About 10 minutes after they had crossed the Upper Glade, they looked back up at it, and saw that the western side had slid. The fracture was about 50 feet below the blast point and 45 inches deep. The lower 6- 8 inches was depth hoar. The snow slid to the ground and traveled for 250 feet This same slope had been closed on 21 December, but was skied anyway by two men. On 22 December, one block of C- 3 High Explosive brought out the entire slide. The lower 14 inches of the snow pack was depth hoar. Thus in 26 days, this slope had developed 6- 8 inches of depth hoar. The Upper North Glade avalanche path averages 30 degrees ( 58%). This area and the " Pali" were kept closed the remainder of the 17th. On 18 January, the State Highway gun crew put three shots in the upper area of the " Pali" with their 75 mm howitzer. Two of the shots were too low, and the third was in the lower and stable portion of the cornice at the top of the slide. After the shooting, two employees of the area wanted to ski the " Pali," but the instructors who were checking the area prevailed upon them to wait until they had put some hand placed charges in the proper shot points. This avalanche is 2,700 feet long, with slopes from 45- 65%. The instructors made up one charge of seven sticks of 40% dynamite plus one stick of C- 3. ( Normal charge for this slope is three to five sticks of C- 3.) The shot was placed at one of the major shot points. Result? The entire slope avalanched with a 10 foot fracture. The hard slab cleared the snow to the ground and tore up the grass and dirt cover underneath. The debris traveled the entire distance of the slide path, reaching the highway which is across the creek and up the opposite slope. Considerable pressure had been put on the ranger to open these slopes during 13- 17 January. COMMENTS Any one of the three examples above could have resulted in a tragic accident. These incidents show the necessity of using adequate charges, and being sure they are detonated in the proper place. This is why a comprehensive " Avalanche Control Plan," complete with picture and diagrams, is a must at any area having even one dangerous avalanche path. The data on the Upper Glade show how fast depth hoar can build under favorable conditions. A snow ranger must constantly check such slopes to determine the extent of " undermining" from depth hoar. 27 |