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Show discovered that the slab was approximately five feet thick, and had swept the entire area clean of snow, down to grass and bedrock. The slab had been split up by numerous large trees on the slope. The slide ran out for about one- half mile and was almost a mile wide at the lower end. COMMENTS The leader concluded that the ski party had little or nothing to do with releasing the slide, but this cannot be completely ruled out as a possibility. It might also have been triggered by the rapidly accumulating wet snow which finally collapsed the weak bottom layer. Three reasons for a false sense of security on the part of the ski party should be noted: 1. The ski pole probe was inadequate in revealing the existence of slab avalanche conditions; 2. The leader kept the party on the crest of the spur, assuming it to be safe; 3. The spur was heavily forested with large trees, giving no evidence that it had ever been subject to slides; these trees, like the ridge position gave an unwarranted feeling of security. Still, the fracturing of the snow, if not the avalanche, reached clear to the ridge top. Avalanches generated by a slab resting on depth hoar can originate in surprisingly thick stands of trees. No. 62- 3 TWIN LAKES, COLORADO 21 January 1962 WEATHER FACTORS During September, 1961, 72 inches of snow was recorded at Berthoud Pass, which is approximately 60 airline miles northeast of Twin Lakes, Colorado. During October and November the weather in the Rocky Mountains warmed, leaving an ice crust on top of the snow at the higher elevations. Additional snow fell during late November and early December, after which it turned quite cold. The lower portions of the snow pack readily turned to depth hoar. During the second week in January, 1962, a 4l- inch storm fell at Berthoud, causing avalanching on nearly all slopes, either back to the ice layer to to the ground. On the evening of Thursday, 18 January, a light snow began which continued throughout Friday. On Saturday, 20 January, the intensity of the snow storm increased, and the S- SW winds were reported gusting to 70 m. p. h. The lifts were unable to operate due to the winds at 72 |
