AGU: Fall meeting, 1996, EOS, V 77, p F197.

The Rise and Decline of Western Ice Columns in Snow, Niwot Ridge, Colorado


Observations of exposed, patterned, vertical ice columns were made late in the 1996 melt season near Niwot Ridge, a continental alpine site in the Colorado Front Range, located at 3500 m. Several techniques were employed in an attempt to determine the origin, growth patterns, and physical properties of these "penitents". Specifically, we tested the hypothesis that the spacing of the columns was similar to derived basal discharge lag distances based on analysis of two seasons of lysimeter snowmelt data. Each individual column was distinguished by an oblong cap of natural debris, regardless of its height relative to the snow surface (-2 to 60 cm). Measured values (n = 52) indicate a mean cap size of 11.2 cm (with the fall line) by 7.2 cm (perpendicular to fall line), and the mean height of columns above the snowpack was 34 cm. Mean spacing of columns (n = 78) was 2.4 m perpendicular to, and 45.04 cm with, the fall line; the correlation of these numbers with lysimeter data varied with respect to discharge period. Full excavation of penitents showed adherence of column bases to a well developed lateral ice lens which was not found in neighboring snow, as well as systems of ice "ribs" which linked one column to the next downslope. Sediment analysis, temperature data, spectral reflectance data, and crystallography images were collected from both the columns and adjoining snow. Ideas on the development of these columns, as well as their importance in the hydrologic cycle, build on previous research, much of which was done during the early 1900s.