Here we provide information on ice columns and frozen rills found in late-season snowpacks in and near the Green Lakes Valley of the Colorado Front Range, USA. The presence of ice columns and frozen rills in late season snowpacks may provide insights with which to understand the spatial distribution of preferential flowpaths in melting snowpacks. In July and August of 1996 and 1997 we found ice columns in every one of the more than 50 snow fields we investigated. The ice columns showed a consistent morphology; each column was approximately 75 cm in vertical extent, with about 5 cm projecting above the snow surface and 70 cm extending into the snowpack. An analysis of variance test shows that the 81 ice columns on the south-facing slopes were significantly greater than the 57 ice columns on the north-facing slope (p = 0.01). There were about 3 ice columns per square metre on the southfacing slopes and 2 ice columns per square metre on the north-facing slopes. There was an interesting hysteresis in snow and ice temperatures that became stronger with increasing depth in adjacent thermocouple arrays. This hysteresis in the temperature profiles is consistent with the release of latent heat from the freezing of greater amounts of liquid water in and near the ice columns compared to the surrounding snowpack. At the Martinelli catchment, spacing between the frozen rills averaged 2.6 m (n = 73). We interpret these “ribs” of solid ice to be the remnants of surface rills. Vertical ice columns were connected to these frozen rills. The ice columns and frozen rills may provide a snapshot or “schematic” diagram of the major flowpaths in a ripe and draining snowpack.

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