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<br />002544 <br /> <br />Not all these impacts are necessarily deleterious; an increase in the <br />area of snowbank edge habitats in alpine areas may, for example, <br />increase the niches available for rare plant species. <br /> <br />Finally, even in the small areas where the study concluded the <br />greatest impacts would occur, the changes involved are unlikely to <br />approach the magnitude of other manmade impacts on mountain eco- <br />systems. Even so, project scientists noted that any change works in <br />phase with other ~mpacts and natural occurrences. Consequently, <br />scientists must be alert to greater than expected total changes. <br /> <br />CONTRACTOR: University of Colorado, Institute.of Arctic and Alpine <br />Research, Boulder, Colorado <br />CONTRACT NO. 14-06-0-7155 <br />PRINCIPAL INVESTIGATOR: J. D. Ives <br />PERIOD: July 1, 1974, to June 30, 1976 <br />FUNDING: FY75 - $35,057 <br />FY76 - $11,675 <br /> <br />The objective of this contract was to develop a methodology to <br />accurately forecast avalanche occurrences through the study of the <br />complex relationship which exists among terrain, climate, snow <br />stratigraphy, and avalanche formation. When the study was initiated <br />in 1971, only a limited amount of climatological data was available <br />for the study area, the Red Mountain, Molas, and Coal Bank Pass <br />regions of the San Juan Mountains. Avalanche processes in this <br />high-incidence region are well understood as the result of this <br />study. . <br /> <br />) <br /> <br />Evidence suggests that avalanche release within subfreezing snow <br />layers is primarily dependent on precipitation to trigger unstable <br />layers deep within the snow cover. While frequency and magnitude <br />are influenced by precipitation rates and amounts, they are deter- <br />mined primarily by the snow structure within the release zone at the <br />time'precipitation loading occurs. Magnitude is affected by the <br />mechanical strength of snow layers in midtrack, for this determines <br />the penetration depth of sliding snow and the volume of the avalanche. <br />The study was able to produce the first approach to an operational, <br />real-time statistical forecast model for major avalanche chutes <br />during the dry and wet seasons with an accuracy of 88 and 82 percent, <br />respectively. It is the first model to be applied to groups of <br />starting zones and individual paths to predict magnitude of avalanche <br />occurrence. <br /> <br />Particular emphasis was placed on the study of fracture lines during <br />the final two study seasons. Attention was directed toward the <br />temperature gradient. Periodic snowpit investigation at these sites <br /> <br />11-9 <br />