Geomorphic Systems of Green Lakes Valley

There are at least three justifications for the examination of the geomorphology of the area in which ecosystem studies are conducted. First, the present landscape and the materials that make it up provide the substrate on which ecosystem development occurs and may impose constraints, such as where soil resources are limited, on that development. Second, the nature of the landscape and the geomorphic processes acting on it often define a large part of the disturbance regime within which ecosystem processes occur (Swanson et al. 1988). Third, the processes of weathering, erosion, sediment transport, and deposition that define geomorphic dynamics within the landscape are themselves ecosystem processes, for example, involving the supply of resources to organisms. In this last context, it is noteworthy that drainage basins (also called watersheds or catchments) were recognized as units of scientific study during a similar time period in both geomorphology and ecology (Slaymaker and Chorley 1964; Bormann and Likens 1967; Chorley 1969). The drainage basin concept, the contention that lakes and streams act to integrate ecological and geomorphic processes, remains important in both sciences and underlies the studies in Green Lakes Valley reviewed here. Over the past 30 years, Niwot Ridge and the adjacent catchment of Green Lakes Valley have been the subject of much research in geomorphology. Building on the studies of Outcalt and MacPhail (1965), White (1968), and Benedict (1970), work has emphasized the study of present-day processes and dynamics, especially of mass wasting in alpine areas. These topics have been reviewed by Caine (1974, 1986), Ives (1980), and Thorn and Loewenherz (1987). Studies of geomorphic processes have been conducted in parallel with work on Pleistocene (3 million to 10,000 yr BP) and Holocene (10,000 yr BP to present) environments in the Colorado Front Range (Madole 1972; Benedict 1973) that have been reviewed by White (1982). This chapter is intended to update those reviews in terms that complement the presentation of ecological phenomena such as nitrogen saturation in the alpine (chapter 5) as well as to refine observations and conclusions of earlier geomorphic studies.

Ice Columns and Frozen Rills in a Warm Snowpack, Green Lakes Valley, Colorado, U.S.A.

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.