Snow compaction effects of nighttime freezing

Artificial compaction of snow is amoung the most drastic of our snow management and engineering techniques. Snow is compacted to improve recreational skiing conditions; to create winter roads, parking lots, and runways; and for use as building material. Compaction increases both the density and hardness of snow. As part of a study to assess some of the hydrologic effects of snow compaction at ski areas, nighttime freezing depths of both compacted and natural snow were measured at two Sierra Nevada sites. The degree of nocturnal refreezing of the snowpack affects the timing of meltwater release on the following day and may partially account for observed differences in runoff from compacted and natural snow. The compacted snow froze an average of 13 cm deeper than the uncompacted snow, based on 16 pairs of measurements. The greater depth of freezing of the compacted snow can be explained by the increase in thermal conductivity with increased density and bonding.