THE AFFECTS OF DUST DEPOSITION ON SUB-ALPINE SNOWPACK, SWAMP ANGEL STUDY PLOT, OURAY COUNTY, COLORADO

The deposition of windblown dust may strongly influence the melting rate of snowpacks within alpine and sub-alpine regions. A study was conducted at a site in the Northwestern San Juan Mountains of Colorado to simulate a sub-alpine dust storm event and to determine which had the greater impact on snowpack melting rates- dust color or chemical composition. This study was conducted within an undisturbed snow plot located at the Swamp Angel Study Plot (SASP) near Red Mountain Pass (N4420911.625, E26822.077, zone 13N). SASP is located within a sheltered basin at an elevation of 3,375 meters (11,072 feet), on a 0-5º, northeast-facing slope and is generally free of dense forest cover. The 10m x 10m snow plot was divided into four parallel tracts (1m x 10m), three of which were artificially sprinkled with dust to a thickness of 0-2mm, the fourth left unaltered for control purposes. Dust samples were pulverized to pass a 200 mesh sieve (0.074 mm) and consisted of light red, light brown, and grey color tones. The composition of each sample was determined by XRD analysis. Snow plot sections (dusted only once) were left exposed to the sun's radiative effects during the spring snowpack accumulation and ablation periods of February, March, and April (data were collected over two seasons, 2005 and 2006). Treated sections were soon buried by new snowfall but then reemerged later in spring (all tracts were also subject to natural air-fall events). Snow water equivalencies (SWE), density, and dust surface exposure data were collected. Analyses of the data suggest that melting rates were greater for progressively darker dusts and that dust color (rather than dust composition) had the greatest affect on the sub-alpine snowpack. Free water released during melt periods transported surficial or source dust layers (through melt columns) to form lower, denser layers (developed by snow storms with high SWE) within the snowpack. The objective of this study was to aid in the understanding of how snowpacks are affected by airborne impurities in a time of global warming, regional drought, dwindling ice and snowpack volume, and diminishing water resources.