Ice columns and frozen rills in a warm snowpack, Green Lakes Valley, Colorado, USA

Here we provide information on ice columns and frozen rills found in late-s eason snowpacks in and near the Green Lakes Valley of the Colorado Front Ra nge, USA. The presence of ice columns and frozen rills in late season snowp acks 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 colu mn was approximately 75 cm in vertical extent, with about 5 cm projecting a bove 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 wer e 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 southfaci ng slopes and 2 ice columns per square metre on the north-facing slopes. Th ere was an interesting hysteresis in snow and ice temperatures that became stronger with increasing depth in adjacent thermocouple arrays. This hyster esis in the temperature profiles is consistent with the release of latent h eat from the freezing of greater amounts of liquid water in and near the ic e columns compared to the surrounding snowpack. At the Martinelli catchment , spacing between the frozen rills averaged 2.6 m (n = 73). We interpret th ese "ribs" of solid ice to be the remnants of surface rids. Vertical ice co lumns were connected to these frozen rills. The ice columns and frozen rill s may provide a snapshot or "schematic" diagram of the major flowpaths in a ripe and draining snowpack.